The EPA Administrator, Gina McCarthy, signed the following
notice on 9/29/2015, and EPA is submitting it for publication in
the Federal Register (FR). While we have taken steps to ensure
the accuracy of this Internet version of the rule, it is not the
official version of the rule for purposes of compliance. Please
refer to the official version in a forthcoming FR publication,
which will appear on the Government Printing Office's FDSys
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Regulations.gov (https://www.regulations.gov) in Docket No. EPA-
HQ-OAR-2010-0682. Once the official version of this document is
published in the FR, this version will be removed from the
Internet and replaced with a link to the official version
Method 325B—Volatile Organic Compounds from Fugitive and Area
Sources:
Sampler Preparation and Analysis
1.0 Scope and Application
1.1 This method describes thermal desorption / gas
chromatography (TD/GC) analysis of volatile organic compounds
(VOCs) from fugitive and area emission sources collected onto
sorbent tubes using passive sampling. It could also be applied
to the TD/GC analysis of VOCs collected using active (pumped)
sampling onto sorbent tubes. The concentration of airborne VOCs
at or near potential fugitive- or area-emission sources may be
determined using this method in combination with Method 325A.
Companion Method 325A (Sampler Deployment and VOC Sample
Collection) describes procedures for deploying the sorbent tubes
and passively collecting VOCs.
1.2 The preferred GC detector for this method is a mass
spectrometer (MS), but flame ionization detectors (FID) may also
be used. Other conventional GC detectors such as electron
capture (ECD), photoionization (PID), or flame photometric (FPD)
may also be used if they are selective and sensitive to the
target compound(s) and if they meet the method performance
criteria provided in this method.
1.3 There are 97 VOCs listed as hazardous air pollutants in Title III of the Clean Air Act Amendments of 1990. Many of these VOC are candidate compounds for this method. Compounds with known uptake rates for CarbographTM 1 TD, CarbopackTM B, or CarbopackTM X are listed in Table 12.1. This method provides performance criteria to demonstrate acceptable performance of the method (or modifications of the method) for monitoring one or more of the compounds listed Table 12.1. If standard passive sampling tubes are packed with other sorbents or used for other analytes than those listed in Table 12.1, then method performance and relevant uptake rates should be verified according to Addendum A to this method or by one of the following national/international standard methods: ISO 16017- 2:2003(E), ASTM D6196-03 (Reapproved 2009), or BS EN 14662- 4:2005 (all incorporated by reference—see §63.14), or reported in the peer-reviewed open literature.
1.4 The analytical approach using TD/GC/MS is based on
previously published EPA guidance in Compendium Method TO-17
(https://www.epa.gov/ttnamti1/airtox.html#compendium) (Reference
1), which describes active (pumped) sampling of VOCs from
ambient air onto tubes packed with thermally stable adsorbents.
1.5 Inorganic gases not suitable for analysis by this
method include oxides of carbon, nitrogen and sulfur, ozone (O3), and other diatomic permanent gases. Other pollutants not suitable for this analysis method include particulate pollutants, (i.e., fumes, aerosols, and dusts), compounds too labile (reactive) for conventional GC analysis, and VOCs that are more volatile than propane.
2.0 Summary of Method
2.1 This method provides procedures for the preparation,
conditioning, blanking, and shipping of sorbent tubes prior to
sample collection.
2.2 Laboratory and field personnel must have experience of
sampling trace-level VOCs using sorbent tubes (References 2,5)
and must have experience operating thermal desorption/GC/multi-
detector instrumentation.
2.3 Key steps of this method as implemented for each
sample tube include: Stringent leak testing under stop flow,
recording ambient temperature conditions, adding internal
standards, purging the tube, thermally desorbing the sampling
tube, refocusing on a focusing trap, desorbing and
transferring/injecting the VOCs from the secondary trap into the
capillary GC column for separation and analysis.
2.4 Water management steps incorporated into this method
include: a) selection of hydrophobic sorbents in the sampling
tube; b) optional dry purging of sample tubes prior to analysis;
and c) additional selective elimination of water during primary
(tube) desorption (if required) by selecting trapping sorbents
and temperatures such that target compounds are quantitatively
retained while water is purged to vent.
3.0 Definitions
(See also Section 3.0 of Method 325A).
3.1 Blanking is the desorption and confirmatory analysis
of conditioned sorbent tubes before they are sent for field
sampling.
3.2 Breakthrough volume and associated relation to passive
sampling. Breakthrough volumes, as applied to active sorbent
tube sampling, equate to the volume of air containing a constant
concentration of analyte that may be passed through a sorbent
tube at a given temperature before a detectable level (5
percent) of the input analyte concentration elutes from the
tube. Although breakthrough volumes are directly related to
active rather than passive sampling, they provide a measure of
the strength of the sorbent-sorbate interaction and therefore
also relate to the efficiency of the passive sampling process.
The best direct measure of passive sampling efficiency is the
stability of the uptake rate. Quantitative passive sampling is
compromised when the sorbent no longer acts as a perfect sink –
i.e., when the concentration of a target analyte immediately
above the sorbent sampling surface no longer approximates to
zero. This causes a reduction in the uptake rate over time. If
the uptake rate for a given analyte on a given sorbent tube
remains relatively constant — i.e., if the uptake rate
determined for 48 hours is similar to that determined for 7 or
14 days—the user can be confident that passive sampling is
occurring at a constant rate. As a general rule of thumb, such
ideal passive sampling conditions typically exist for
analyte:sorbent combinations where the breakthrough volume
exceeds 100 L (Reference 4).
3.3 Continuing calibration verification sample (CCV).
Single level calibration samples run periodically to confirm
that the analytical system continues to generate sample results
within acceptable agreement to the current calibration curve.
3.4 Focusing trap is a cooled, secondary sorbent trap
integrated into the analytical thermal desorber. It typically
has a smaller i.d. and lower thermal mass than the original
sample tube allowing it to effectively refocus desorbed analytes
and then heat rapidly to ensure efficient transfer/injection
into the capillary GC analytical column.
3.5 High Resolution Capillary Column Chromatography uses
fused silica capillary columns with an inner diameter of 320 μm
or less and with a stationary phase film thickness of 5 μm or
less.
3.6 h is time in hours.
3.7 i.d. is inner diameter.
3.8 min is time in minutes.
3.9 Method Detection Limit is the lowest level of analyte
that can be detected in the sample matrix with 99% confidence.
3.10 MS-SCAN is the mode of operation of a GC quadrupole
mass spectrometer detector that measures all ions over a given
mass range over a given period of time.
3.11 MS-SIM is the mode of operation of a GC quadrupole
mass spectrometer detector that measures only a single ion or a
selected number of discrete ions for each analyte.
3.12 o.d. is outer diameter.
3.13 ppbv is parts per billion by volume.
3.14 Thermal desorption is the use of heat and a flow of
inert (carrier) gas to extract volatiles from a solid matrix. No
solvent is required.
3.15 Total ion chromatogram is the chromatogram produced
from a mass spectrometer detector collecting full spectral
information.
3.16 Two-stage thermal desorption is the process of
thermally desorbing analytes from a sorbent tube,
reconcentrating them on a focusing trap (see Section 3.4), which
is then itself rapidly heated to “inject” the concentrated
compounds into the GC analyzer.
3.17 VOC is volatile organic compound.
4.0 Analytical Interferences
4.1 Interference from Sorbent Artifacts. Artifacts may
include target analytes as well as other VOC that co-elute
chromatographically with the compounds of interest or otherwise
interfere with the identification or quantitation of target
analytes.
4.1.1 Sorbent decomposition artifacts are VOCs that form when sorbents degenerate, e.g., when exposed to reactive species during sampling. For example, benzaldehyde, phenol, and acetophenone artifacts are reported to be formed via oxidation of the polymeric sorbent Tenax® when sampling high concentration (100-500 ppb) ozone atmospheres (Reference 5).
4.1.2 Preparation and storage artifacts are VOCs that were
not completely cleaned from the sorbent tube during conditioning
or that are an inherent feature of that sorbent at a given
temperature.
4.2 Humidity. Moisture captured during sampling can
interfere with VOC analysis. Passive sampling using tubes packed
with hydrophobic sorbents, like those described in this method,
minimizes water retention. However, if water interference is
found to be an issue under extreme conditions, one or more of
the water management steps described in Section 2.4 can be
applied.
4.3 Contamination from Sample Handling. The type of
analytical thermal desorption equipment selected should exclude
the possibility of outer tube surface contamination entering the
sample flow path (see Section 6.6). If the available system does
not meet this requirement, sampling tubes and caps must be
handled only while wearing clean, white cotton or powder free
nitrile gloves to prevent contamination with body oils, hand
lotions, perfumes, etc.
5.0 Safety
5.1 This method does not address all of the safety
concerns associated with its use. It is the responsibility of
the user of this standard to establish appropriate field and
laboratory safety and health practices prior to use.
5.2 Laboratory analysts must exercise extreme care in
working with high-pressure gas cylinders.
5.3 Due to the high temperatures involved, operators must
use caution when conditioning and analyzing tubes.
6.0 Equipment and Supplies
6.1 Tube Dimensions and Materials. The sampling tubes for
this method are 3.5-inches (89 mm) long, 1/4 inch (6.4 mm) o.d.,
and 5 mm i.d. passive sampling tubes (see Figure 6.1). The tubes
are made of inert-coated stainless steel with the central
section (up to 60 mm) packed with sorbent, typically supported
between two 100 mesh stainless steel gauze. The tubes have a
cross sectional area of 19.6 square mm (5 mm i.d.). When used
for passive sampling, these tubes have an internal diffusion
(air) gap (DG) of 1.5 cm between the sorbent retaining gauze at
the sampling end of the tube, and the gauze in the diffusion
cap.
Figure 6.1. Cross Section View of Passive Sorbent Tube
6.2 Tube Conditioning Apparatus.
6.2.1 Freshly packed or newly purchased tubes must be
conditioned as described in Section 9 using an appropriate
dedicated tube conditioning unit or the thermal desorber. Note
that the analytical TD system should be used for tube
conditioning if it supports a dedicated tube conditioning mode
in which effluent from contaminated tubes is directed to vent
without passing through key parts of the sample flow path such
as the focusing trap.
6.2.2 Dedicated tube conditioning units must be leak-tight
to prevent air ingress, allow precise and reproducible
temperature selection (±5 C), offer a temperature range at least
as great as that of the thermal desorber, and support inert gas
flows in the range up to 100 mL/min.
Note: For safety and to avoid laboratory contamination, effluent gases from freshly packed or highly contaminated tubes should be passed through a charcoal filter during the conditioning process to prevent desorbed VOCs from polluting the laboratory atmosphere.
6.3 Tube Labeling.
6.3.1 Label the sample tubes with a unique permanent
identification number and an indication of the sampling end of
the tube. Labeling options include etching and TD-compatible
electronic (radio frequency identification (RFID)) tube labels.
6.3.2 To avoid contamination, do not make ink markings of
any kind on clean sorbent tubes or apply adhesive labels.
Note: TD-compatible electronic (RFID) tube labels are available commercially and are compatible with some brands of thermal desorber. If used, these may be programmed with relevant tube and sample information, which can be read and automatically transcribed into the sequence report by the TD system (see Section 8.6 of Method 325A).
6.4 Blank and Sampled Tube Storage Apparatus
6.4.1 Long-term storage caps. Seal clean, blank and
sampled sorbent tubes using inert, long-term tube storage caps
comprising non-greased, 2-piece, 0.25-inch, metal SwageLok®-type
screw caps fitted with combined polytetrafluoroethylene
ferrules.
6.4.2 Storage and transportation containers. Use clean
glass jars, metal cans or rigid, non-emitting polymer boxes.
Note: You may add a small packet of new activated charcoal or charcoal/silica gel to the shipping container for storage and transportation of batches of conditioned sorbent tubes prior to use. Coolers without ice packs make suitable shipping boxes for containers of tubes because the coolers help to insulate the samples from extreme temperatures (e.g., if left in a parked vehicle).
6.5 Unheated GC Injection Unit for Loading Standards onto
Blank Tubes. A suitable device has a simple push fit or finger-
tightening connector for attaching the sampling end of blank
sorbent tubes without damaging the tube. It also has a means of
controlling carrier gas flow through the injector and attached
sorbent tube at 50-100 mL/min and includes a low emission septum
cap that allows the introduction of gas or liquid standards via
appropriate syringes. Reproducible and quantitative transfer of
higher boiling compounds in liquid standards is facilitated if
the injection unit allows the tip of the syringe to just touch
the sorbent retaining gauze inside the tube.
6.6 Thermal Desorption Apparatus. The manual or automated
thermal desorption system must heat sorbent tubes while a
controlled flow of inert (carrier) gas passes through the tube
and out of the sampling end. The apparatus must also incorporate
a focusing trap to quantitatively refocus compounds desorbed
from the tube. Secondary desorption of the focusing trap should
be fast/efficient enough to transfer the compounds into the high
resolution capillary GC column without band broadening and
without any need for further pre- or on-column focusing. Typical
TD focusing traps comprise small sorbent traps (Reference 16)
that are electrically-cooled using multistage Peltier cells
(References 17, 18). The direction of gas flow during trap
desorption should be the reverse of that used for focusing to
extend the compatible analyte volatility range. Closed cycle
coolers offer another cryogen-free trap cooling option. Other TD
system requirements and operational stages are described in
Section 11 and in Figures 17-2 through 17-4.
6.7 Thermal Desorber - GC Interface.
6.7.1 The interface between the thermal desorber and the
GC must be heated uniformly and the connection between the
transfer line insert and the capillary GC analytical column
itself must be leak tight.
6.7.2 A portion of capillary column can alternatively be
threaded through the heated transfer line / TD interface and
connected directly to the thermal desorber.
Note: Use of a metal syringe-type needle or unheated length
of fused silica pushed through the septum of a conventional GC
injector is not permitted as a means of interfacing the thermal
desorber to the chromatograph. Such connections result in cold
spots, cause band broadening and are prone to leaks.
6.8 GC/MS Analytical Components.
6.8.1 The GC system must be capable of temperature
programming and operation of a high resolution capillary column.
Depending on the choice of column (e.g., film thickness) and the
volatility of the target compounds, it may be necessary to cool
the GC oven to subambient temperatures (e.g., -50 C) at the start of the run to allow resolution of very volatile organic compounds.
6.8.2 All carrier gas lines supplying the GC must be
constructed from clean stainless steel or copper tubing. Non-
polytetrafluoroethylene thread sealants. Flow controllers,
cylinder regulators, or other pneumatic components fitted with
rubber components are not suitable.
6.9 Chromatographic Columns. High-resolution, fused silica
or equivalent capillary columns that provide adequate separation
of sample components to permit identification and quantitation
of target compounds must be used.
Note: 100-percent methyl silicone or 5-percent phenyl, 95- percent methyl silicone fused silica capillary columns of 0.25- to 0.32-mm i.d. of varying lengths and with varying thicknesses
of stationary phase have been used successfully for non-polar
and moderately polar compounds. However, given the diversity of
potential target lists, GC column choice is left to the
operator, subject to the performance criteria of this method.
6.10 Mass Spectrometer. Linear quadrupole, magnetic
sector, ion trap or time-of-flight mass spectrometers may be
used provided they meet specified performance criteria. The mass
detector must be capable of collecting data from 35 to 300
atomic mass units (amu) every 1 second or less, utilizing 70
volts (nominal) electron energy in the electron ionization mode,
and producing a mass spectrum that meets all the instrument
performance acceptance criteria in Section 9 when 50 g or less of p-bromofluorobenzene is analyzed.
7.0 Reagents and Standards
7.1 Sorbent Selection.
7.1.1 Use commercially packed tubes meeting the
requirements of this method or prepare tubes in the laboratory
using sieved sorbents of particle size in the range 20 to 80
mesh that meet the retention and quality control requirements of
this method.
7.1.2 This passive air monitoring method can be used
without the evaluation specified in Addendum A if the type of
tubes described in Section 6.1 are packed with 4-6 cm (typically
400-650 mg) of the sorbents listed in Table 12.1 and used for
the respective target analytes.
Note: Although CarbopackTM X is the optimum sorbent choice
for passive sampling of 1,3-butadiene, recovery of compounds
with vapor pressure lower than benzene may be difficult to
achieve without exceeding sorbent maximum temperature
limitations (see Table 8.1). See ISO 16017-2:2003(E) or ASTM
D6196-03 (Reapproved 2009) (both incorporated by reference—see
§63.14) for more details on sorbent choice for air monitoring
using passive sampling tubes.
7.1.3 If standard passive sampling tubes are packed with
other sorbents or used for analytes other than those tabulated
in Section 12.0, method performance and relevant uptake rates
should be verified according to Addendum A to this method or by
following the techniques described in one of the following
national/international standard methods: ISO 16017-2:2003(E),
ASTM D6196-03 (Reapproved 2009), or BS EN 14662-4:2005 (all
incorporated by reference—see §63.14) – or reported in the peer-
reviewed open literature. A summary table and the supporting
evaluation data demonstrating the selected sorbent meets the
requirements in Addendum A to this method must be submitted to
the regulatory authority as part of a request to use an
alternative sorbent.
7.1.4 Passive (diffusive) sampling and thermal desorption
methods that have been evaluated at relatively high atmospheric
concentrations (i.e., mid-ppb to ppm) and published for use in
workplace air and industrial/mobile source emissions testing
(References 9-20) may be applied to this procedure. However, the
validity of any shorter term uptake rates must be verified and
adjusted if necessary for the longer monitoring periods required
by this method by following procedures described in Addendum A
to this method or those presented in national/international
standard methods: ISO 16017-2:2003(E), ASTM D6196-03 (Reapproved
2009), or BS EN 14662-4:2005 (all incorporated by reference-see
§63.14).
7.1.5 Suitable sorbents for passive sampling must have
breakthrough volumes of at least 20 L (preferably >100 L) for
the compounds of interest and must quantitatively release the
analytes during desorption without exceeding maximum
temperatures for the sorbent or instrumentation.
7.1.6 Repack/replace the sorbent tubes or demonstrate tube
performance following the requirements in Addendum A to this
method at least every 2 years or every 50 uses, whichever occurs
first.
7.2 Gas Phase Standards.
7.2.1 Static or dynamic standard atmospheres may be used
to prepare calibration tubes and/or to validate passive sampling
uptake rates and can be generated from pure chemicals or by
diluting concentrated gas standards. The standard atmosphere
must be stable at ambient pressure and accurate to ±10 percent
of the target gas concentration. It must be possible to maintain
standard atmosphere concentrations at the same or lower levels
than the target compound concentration objectives of the test.
Test atmospheres used for validation of uptake rates must also
contain at least 35 percent relative humidity.
Note: Accurate, low-(ppb-) level gas-phase VOC standards are difficult to generate from pure materials and may be unstable depending on analyte polarity and volatility. Parallel monitoring of vapor concentrations with alternative methods, such as pumped sorbent tubes or sensitive/selective on-line detectors, may be necessary to minimize uncertainty. For these reasons, standard atmospheres are rarely used for routine calibration.
7.2.2 Concentrated, pressurized gas phase standards.
Accurate (±5 percent or better), concentrated gas phase
standards supplied in pressurized cylinders may also be used for
calibration. The concentration of the standard should be such
that a 0.5 - 5.0 mL volume contains approximately the same mass
of analytes as will be collected from a typical air sample.
7.2.3 Follow manufacturer’s guidelines concerning storage
conditions and recertification of the concentrated gas phase
standard. Gas standards must be recertified a minimum of once
every 12 months.
7.3 Liquid Standards. Target analytes can also be
introduced to the sampling end of sorbent tubes in the form of
liquid calibration standards.
7.3.1 The concentration of liquid standards must be such
that an injection of 0.5-2 μl of the solution introduces the
same mass of target analyte that is expected to be collected
during the passive air sampling period.
7.3.2 Solvent Selection. The solvent selected for the
liquid standard must be pure (contaminants <10 percent of
minimum analyte levels) and must not interfere
chromatographically with the compounds of interest.
7.3.3 If liquid standards are sourced commercially, follow
manufacturer’s guidelines concerning storage conditions and
shelf life of unopened and opened liquid stock standards.
Note: Commercial VOC standards are typically supplied in volatile or non-interfering solvents such as methanol.
7.3.4 Working standards must be stored at 6 C or less and used or discarded within two weeks of preparation.
7.4 Gas Phase Internal Standards.
7.4.1 Gas-phase deuterated or fluorinated organic
compounds may be used as internal standards for MS-based
systems.
7.4.2 Typical compounds include deuterated toluene,
perfluorobenzene and perfluorotoluene.
7.4.3 Use multiple internal standards to cover the
volatility range of the target analytes.
7.4.4 Gas-phase standards must be obtained in pressurized
cylinders and containing vendor certified gas concentrations
accurate to ±5 percent. The concentration should be such that
the mass of internal standard components introduced is similar
to those of the target analytes collected during field
monitoring.
7.5 Preloaded Standard Tubes. Certified, preloaded
standard tubes, accurate within ±5 percent for each analyte at
the microgram level and ±10 percent at the nanogram level, are
available commercially and may be used for auditing and quality
control purposes. (See Section 9.5 for audit accuracy evaluation
criteria.) Certified preloaded tubes may also be used for
routine calibration.
Note: Proficiency testing schemes are also available for TD/GC/MS analysis of sorbent tubes preloaded with common analytes such as benzene, toluene, and xylene.
7.6 Carrier Gases. Use inert, 99.999-percent or higher
purity helium as carrier gas. Oxygen and organic filters must be
installed in the carrier gas lines supplying the analytical
system according to the manufacturer’s instructions. Keep
records of filter and oxygen scrubber replacement.
8.0 Sorbent Tube Handling (Before and After Sampling)
8.1 Sample Tube Conditioning.
8.1.1 Sampling tubes must be conditioned using the
apparatus described in Section 6.2.
8.1.2 New tubes should be conditioned for 2 hours to
supplement the vendor’s conditioning procedure. Recommended
temperatures for tube conditioning are given in Table 8.1.
8.1.3 After conditioning, the blank must be verified on
each new sorbent tube and on 10 percent of each batch of
reconditioned tubes. See Section 9.0 for acceptance criteria.
Table 8.1 Example Sorbent Tube Conditioning Parameters
Sampling Sorbent
Maximum Temperature (C)
Conditioning
Temperature
(C)
Carrier Gas Flow
Rate
Carbotrap C CarbopackTM C Anasorb GCB2 CarbographTM 1 TD Carbotrap CarbopackTM B Anasorb GCB1
>400
350
100 mL/min
Tenax TA CarbopackTM X
350
330
100 mL/min
8.2 Capping, Storage and Shipment of Conditioned Tubes.
8.2.1 Conditioned tubes must be sealed using long-term
storage caps (see Section 6.4) pushed fully down onto both ends
of the PS sorbent tube, tightened by hand and then tighten an
additional quarter turn using an appropriate tool.
8.2.2 The capped tubes must be kept in appropriate
containers for storage and transportation (see Section 6.4.2).
Containers of sorbent tubes may be stored and shipped at ambient
temperature and must be kept in a clean environment.
8.2.3 You must keep batches of capped tubes in their
shipping boxes or wrap them in uncoated aluminum foil before
placing them in their storage container, especially before air
freight, because the packaging helps hold caps in position if
the tubes get very cold.
8.3 Calculating the Number of Tubes Required for a
Monitoring Exercise.
8.3.1 Follow guidance given in Method 325A to determine
the number of tubes required for site monitoring.
8.3.2 The following additional samples will also be
required: Laboratory blanks as specified in Section 9.1.2 (one
per analytical sequence minimum), field blanks as specified in
Section 9.3.2 (two per sampling period minimum), CCV tubes as
specified in Section 10.9.4. (at least one per analysis sequence
or every 24 hours), and duplicate samples as specified in
Section 9.4 (at least one duplicate sample is required for every
10 sampling locations during each monitoring period).
8.4 Sample Collection.
8.4.1 Allow the tubes to equilibrate with ambient
temperature (approximately 30 minutes to 1 hour) at the
monitoring location before removing them from their
storage/shipping container for sample collection.
8.4.2 Tubes must be used for sampling within 30 days of
conditioning (Reference 4).
8.4.3 During field monitoring, the long-term storage cap
at the sampling end of the tube is replaced with a diffusion cap
and the whole assembly is arranged vertically, with the sampling
end pointing downward, under a protective hood or shield – See
Section 6.1 of Method 325A for more details.
8.5 Sample Storage.
8.5.1 After sampling, tubes must be immediately resealed
with long-term storage caps and placed back inside the type of
storage container described in Section 6.4.2.
8.5.2 Exposed tubes may not be placed in the same
container as clean tubes. They should not be taken back out of
the container until ready for analysis and after they have had
time to equilibrate with ambient temperature in the laboratory.
8.5.3 Sampled tubes must be inspected before analysis to
identify problems such as loose or missing caps, damaged tubes,
tubes that appear to be leaking sorbent or container
contamination. Any and all such problems must be documented
together with the unique identification number of the tube or
tubes concerned. Affected tubes must not be analyzed but must be
set aside.
8.5.4 Intact tubes must be analyzed within 30 days of the
end of sample collection (within one week for limonene, carene,
bis-chloromethyl ether, labile sulfur or nitrogen-containing
compounds, and other reactive VOCs).
Note: Ensure ambient temperatures stay below 23 °C during transportation and storage. Refrigeration is not normally required unless the samples contain reactive compounds or cannot be analyzed within 30 days. If refrigeration is used, the atmosphere inside the refrigerator must be clean and free of organic solvents.
9.0 Quality Control
9.1 Laboratory Blank. The analytical system must be
demonstrated to be contaminant free by performing a blank
analysis at the beginning of each analytical sequence to
demonstrate that the secondary trap and TD/GC/MS analytical
equipment are free of any significant interferents.
9.1.1 Laboratory blank tubes must be prepared from tubes
that are identical to those used for field sampling.
9.1.2 Analysis of at least one laboratory blank is
required per analytical sequence. The laboratory blank must be
stored in the laboratory under clean, controlled ambient
temperature conditions.
9.1.3 Laboratory blank/artifact levels must meet the
requirements of Section 9.2.2 (see also Table 17.1). If the
laboratory blank does not meet requirements, stop and perform
corrective actions and then re-analyze laboratory blank to
ensure it meets requirements.
9.2 Tube Conditioning.
9.2.1 Conditioned tubes must be demonstrated to be free of
contaminants and interference by running 10 percent of the blank
tubes selected at random from each conditioned batch under
standard sample analysis conditions (see Section 8.1).
9.2.2 Confirm that artifacts and background contamination
are ≤ 0.2 ppbv or less than three times the detection limit of
the procedure or less than 10 percent of the target compound(s)
mass that would be collected if airborne concentrations were at
the regulated limit value, whichever is larger. Only tubes that
meet these criteria can be used for field monitoring, field or
laboratory blanks, or for system calibration.
9.2.3 If unacceptable levels of VOCs are observed in the
tube blanks, then the processes of tube conditioning and
checking the blanks must be repeated.
9.3 Field Blanks.
9.3.1 Field blank tubes must be prepared from tubes that
are identical to those used for field sampling – i.e., they
should be from the same batch, have a similar history, and be
conditioned at the same time.
9.3.2 Field blanks must be shipped to the monitoring site
with the sampling tubes and must be stored at the sampling
location throughout the monitoring exercise. The field blanks
must be installed under a protective hood/cover at the sampling
location, but the long-term storage caps must remain in place
throughout the monitoring period (see Method 325A). The field
blanks are then shipped back to the laboratory in the same
container as the sampled tubes. One field blank tube is required
for every 10 sampled tubes on a monitoring exercise and no less
than two field blanks should be collected, regardless of the
size of the monitoring study.
9.3.3 Field blanks must contain no greater than one-third
of the measured target analyte or compliance limit for field
samples (see Table 17.1). If either field blank fails, flag all
data that do not meet this criterion with a note that the
associated results are estimated and likely to be biased high
due to field blank background.
9.4 Duplicate Samples. Duplicate (co-located) samples
collected must be analyzed and reported as part of method
quality control. They are used to evaluate sampling and analysis
precision. Relevant performance criteria are given in Section
9.9.
9.5 Method Performance Criteria. Unless otherwise noted,
monitoring method performance specifications must be
demonstrated for the target compounds using the procedures
described in Addendum A to this method and the statistical
approach presented in Method 301.
9.6 Method Detection Limit. Determine the method detection limit under the analytical conditions selected (see Section 11.3) using the procedure in Section 15 of Method 301. The method detection limit is defined for each system by making seven replicate measurements of a concentration of the compound of interest within a factor of five of the detection limit. Compute the standard deviation for the seven replicate concentrations, and multiply this value by three. The results should demonstrate that the method is able to detect analytes such as benzene at concentrations as low as 50 ppt or 1/3rd (preferably 1/10th) of the lowest concentration of interest, whichever is larger.
Note: Determining the detection limit may be an iterative process as described in 40 CFR part 136, Appendix B.
9.7 Analytical Bias. Analytical bias must be demonstrated
to be within ±30 percent using Equation 9.1. Analytical bias
must be demonstrated during initial setup of this method and as
part of the CCV carried out with every sequence of 10 samples or
less (see Section 9.14). Calibration standard tubes (see Section
10.0) may be used for this purpose.
AnalyticalBias SpikedValue MeasuredValue100 SpikedValue
Eq. 9.1
Where:
Spiked Value = A known mass of VOCs added to the tube.
Measured Value = Mass determined from analysis of the tube. 9.8 Analytical Precision. Demonstrate an analytical
precision within ±20 percent using Equation 9.2. Analytical
precision must be demonstrated during initial setup of this
method and at least once per year. Calibration standard tubes
may be used (see Section 10.0) and data from CCV may also be
applied for this purpose.
Where:
A1 =
A2 =
AnalyticalPrecision A1 A2100 Eq. 9.2 A
A measurement value taken from one spiked tube.
A measurement value taken from a second spiked tube.
The average of A1 and A2.
9.9 Field Replicate Precision. Use Equation 9.3 to
determine and report replicate precision for duplicate field
samples (see Section 9.4). The level of agreement between
duplicate field samples is a measure of the precision achievable
for the entire sampling and analysis procedure. Flag data sets
for which the duplicate samples do not agree within 30 percent.
Field Precision F1F2100 Eq. 9.3 F
Where:
F1 = A measurement value (mass) taken from one of the two field replicate tubes used in sampling.
A =
F2 = A measurement value (mass) taken from the second of two field replicate tubes used in sampling.
F = The average of F1 and F2.
9.10 Desorption Efficiency and Compound Recovery. The
efficiency of the thermal desorption method must be determined.
9.10.1 Quantitative (>95 percent) compound recovery must
be demonstrated by repeat analyses on a same standard tube.
9.10.2 Compound recovery through the TD system can also be
demonstrated by comparing the calibration check sample response
factor obtained from direct GC injection of liquid standards
with that obtained from thermal desorption analysis response
factor using the same column under identical conditions.
9.10.3 If the relative response factors obtained for one
or more target compounds introduced to the column via thermal
desorption fail to meet the criteria in Section 9.10.1, you must
adjust the TD parameters to meet the criteria and repeat the
experiment. Once the thermal desorption conditions have been
optimized, you must repeat this test each time the analytical
system is recalibrated to demonstrate continued method
performance.
9.11 Audit Samples. Certified reference standard samples
must be used to audit this procedure (if available). Accuracy
within 30 percent must be demonstrated for relevant ambient air
concentrations (0.5 to 25 ppb).
9.12 Mass Spectrometer Tuning Criteria. Tune the mass
spectrometer (if used) according to manufacturer’s
specifications. Verify the instrument performance by analyzing a
50 g injection of bromofluorobenzene. Prior to the beginning of each analytical sequence or every 24 hours during continuous
GC/MS operation for this method demonstrate that the
bromofluorobenzene tuning performance criteria in Table 9.1 have
been met.
Table 9.1 GC/MS Tuning Criteria1
Target Mass
Rel. To Mass
Lower Limit %
Upper Limit %
50
95
8
40
75
95
30
66
95
95
100
100
96
95
5
9
173
174
0
2
174
95
50
120
175
174
4
9
176
174
93
101
177
176
5
9
1 All ion abundances must be normalized to m/z 95, the nominal base peak, even though the ion abundance of m/z 174 may be up to 120 percent that of m/z 95.
9.13 Routine CCV at the Start of a Sequence. Run CCV
before each sequence of analyses and after every tenth sample to
ensure that the previous multi-level calibration (see Section
10.6.3) is still valid.
9.13.1 The sample concentration used for the CCV should be
near the mid-point of the multi-level calibration range.
9.13.2 Quantitation software must be updated with response
factors determined from the CCV standard. The percent deviation
between the initial calibration and the CCV for all compounds
must be within 30 percent.
9.14 CCV at the End of a Sequence. Run another CCV after
running each sequence of samples. The initial CCV for a
subsequent set of samples may be used as the final CCV for a
previous analytical sequence, provided the same analytical
method is used and the subsequent set of samples is analyzed
immediately (within 4 hours) after the last CCV.
9.15 Additional Verification. Use a calibration check
standard from a second, separate source to verify the original
calibration at least once every three months.
9.16 Integration Method. Document the procedure used for
integration of analytical data including field samples,
calibration standards and blanks.
9.17 QC Records. Maintain all QC reports/records for each
TD/GC/MS analytical system used for application of this method.
Routine quality control requirements for this method are listed
below and summarized in Table 17.1.
10.0 Calibration and Standardization
10.1 Calibrate the analytical system using standards
covering the range of analyte masses expected from field
samples.
10.2 Analytical results for field samples must fall within
the calibrated range of the analytical system to be valid.
10.3 Calibration standard preparation must be fully
traceable to primary standards of mass and/or volume, and/or be
confirmed using an independent certified reference method.
10.3.1 Preparation of calibration standard tubes from
standard atmospheres.
10.3.1.1 Subject to the requirements in Section 7.2.1,
low-level standard atmospheres may be introduced to clean,
conditioned sorbent tubes in order to produce calibration
standards.
10.3.1.2 The standard atmosphere generator or system must
be capable of producing sufficient flow at a constant rate to
allow the required analyte mass to be introduced within a
reasonable time frame and without affecting the concentration of
the standard atmosphere itself.
10.3.1.3 The sampling manifold may be heated to minimize
risk of condensation but the temperature of the gas delivered to
the sorbent tubes may not exceed 100 F.
10.3.1.4 The flow rates passed through the tube should be
in the order of 50-100 mL/min and the volume of standard
atmosphere sampled from the manifold or chamber must not exceed
the breakthrough volume of the sorbent at the given temperature.
10.4 Preparation of calibration standard tubes from
concentrated gas standards.
10.4.1 If a suitable concentrated gas standard (see
Section 7.2.2) can be obtained, follow the manufacturer’s
recommendations relating to suitable storage conditions and
product lifetime.
10.4.2 Introduce precise 0.5 to 500.0 mL aliquots of the
standard to the sampling end of conditioned sorbent tubes in a
50-100 mL/min flow of pure carrier gas.
Note: This can be achieved by connecting the sampling end of the tube to an unheated GC injector (see Section 6.6) and introducing the aliquot of gas using a suitable gas syringe. Gas sample valves could alternatively be used to meter the standard gas volume.
10.4.3 Each sorbent tube should be left connected to the
flow of gas for 2 minutes after standard introduction. As soon
as each spiked tube is removed from the injection unit, seal it
with long-term storage caps and place it in an appropriate tube
storage/transportation container if it is not to be analyzed
within 24 hours.
10.5 Preparation of calibration standard tubes from liquid
standards.
10.5.1 Suitable standards are described in Section 7.3.
10.5.2 Introduce precise 0.5 to 2 μl aliquots of liquid
standards to the sampling end of sorbent tubes in a flow (50-100
mL/min) of carrier gas using a precision syringe and an unheated
injector (Section 6.5). The flow of gas should be sufficient to
completely vaporize the liquid standard.
Note: If the analytes of interest are higher boiling than n-decane, reproducible analyte transfer to the sorbent bed is optimized by allowing the tip of the syringe to gently touch the sorbent retaining gauze at the sampling end of the tube.
10.5.3 Each sorbent tube is left connected to the flow of
gas for 5 minutes after liquid standard introduction.
10.5.3.1 As soon as each spiked tube is removed from the
injection unit, seal it with long-term storage caps and place it
in an appropriate tube storage container if it is not to be
analyzed within 24 hours.
Note: In cases where it is possible to selectively purge the solvent from the tube while all target analytes are quantitatively retained, a larger 2 μL injection may be made for optimum accuracy. However, if the solvent cannot be selectively purged and will be present during analysis, the injection volume should be as small as possible (e.g., 0.5 μL) to minimize solvent interference.
Note: This standard preparation technique requires the entire liquid plug including the tip volume be brought into the syringe barrel. The volume in the barrel is recorded, the syringe is inserted into the septum of the spiking apparatus. The liquid is then quickly injected. Any remaining liquid in the
syringe tip is brought back into the syringe barrel. The volume
in the barrel is recorded and the amount spiked onto the tube is
the difference between the before spiking volume and the after
spiking volume. A bias occurs with this method when sample is
drawn continuously up into the syringe to the specified volume
and the calibration solution in the syringe tip is ignored.
10.6 Preparation of calibration standard tubes from
multiple standards.
10.6.1 If it is not possible to prepare one standard
containing all the compounds of interest (e.g., because of
chemical reactivity or the breadth of the volatility range),
standard tubes can be prepared from multiple gas or liquid
standards.
10.6.2 Follow the procedures described in Sections 10.4
and 10.5, respectively, for introducing each gas and/or liquid
standard to the tube and load those containing the highest
boiling compounds of interest first and the lightest species
last.
10.7 Additional requirements for preparation of
calibration tubes.
10.7.1 Storage of Calibration Standard Tubes
10.7.1.1 Seal tubes with long-term storage caps
immediately after they have been disconnected from the standard
loading manifold or injection apparatus.
10.7.1.2 Calibration standard tubes may be stored for no
longer than 30 days and should be refrigerated if there is any
risk of chemical interaction or degradation. Audit standards
(see section 9.11) are exempt from this criteria and may be
stored for the shelf-life specified on their certificates.
10.8 Keep records for calibration standard tubes to
include the following:
10.8.1 The stock number of any commercial liquid or gas
standards used.
10.8.2 A chromatogram of the most recent blank for each
tube used as a calibration standard together with the associated
analytical conditions and date of cleaning.
10.8.3 Date of standard loading.
10.8.4 List of standard components, approximate masses and
associated confidence levels.
10.8.5 Example analysis of an identical standard with
associated analytical conditions.
10.8.6 A brief description of the method used for standard
preparation.
10.8.7 The standard’s expiration date.
10.9 TD/GC/MS using standard tubes to calibrate system
response.
10.9.1 Verify that the TD/GC/MS analytical system meets
the instrument performance criteria given in Section 9.1.
10.9.2 The prepared calibration standard tubes must be
analyzed using the analytical conditions applied to field
samples (see Section 11.0) and must be selected to ensure
quantitative transfer and adequate chromatographic resolution of
target compounds, surrogates, and internal standards in order to
enable reliable identification and quantitation of compounds of
interest. The analytical conditions should also be sufficiently
stringent to prevent buildup of higher boiling, non-target
contaminants that may be collected on the tubes during field
monitoring.
10.9.3 Calibration range. Each TD/GC/MS system must be
calibrated at five concentrations that span the monitoring range
of interest before being used for sample analysis. This initial
multi-level calibration determines instrument sensitivity under
the analytical conditions selected and the linearity of GC/MS
response for the target compounds. One of the calibration points
must be within a factor of five of the detection limit for the
compounds of interest.
10.9.4 One of the calibration points from the initial
calibration curve must be at the same concentration as the daily
CCV standard (e.g., the mass collected when sampling air at
typical concentrations).
10.9.5 Calibration frequency. Each GC/MS system must be
recalibrated with a full 5-point calibration curve following
corrective action (e.g., ion source cleaning or repair, column
replacement) or if the instrument fails the daily calibration
acceptance criteria.
10.9.5.1 CCV checks must be carried out on a regular
routine basis as described in Section 9.14.
10.9.5.2 Quantitation ions for the target compounds are
shown in Table 10.1. Use the primary ion unless interferences
are present, in which case you should use a secondary ion.
Table 10.1 Clean Air Act Volatile Organic Compounds for Passive
Sorbent Sampling
Compound
CAS No.
BP (C)
Vapor pressure (mmHg)a
MWb
Characteristic
Ion(s)
Primary
Secondary
1,1-Dichloroethene
75-35-4
32
500
96.9
61
96
3-Chloropropene
107-05-1
44.5
340
76.5
76
41,39,78
1,1,2-Trichloro-1,2,2-
trifluoroethane
1,1-Dichloroethane
75-34-3
57.0
230
99
63
65, 83,
85, 98,
100.
1,2-Dichloroethane
107-06-2
83.5
61.5
99
62
98
1,1,1-Trichloroethane
71-55-6
74.1
100
133.4
97
99,61
Benzene
71-43-2
80.1
76.0
78
78
Carbon tetrachloride
56-23-5
76.7
90.0
153.8
117
119
1,2-Dichloropropane
78-87-5
97.0
42.0
113
63
112
Trichloroethene
79-01-6
87.0
20.0
131.4
95
97, 130, 132
1,1,2-Trichloroethane
79-00-5
114
19.0
133.4
83
97, 85
Toluene
108-88-3
111
22.0
92
92
91
Tetrachloroethene
127-18-4
121
14.0
165.8
164
129, 131, 166
Chlorobenzene
108-90-7
132
8.8
112.6
112
77, 114
Ethylbenzene
100-41-4
136
7.0
106
91
106
m,p-Xylene
108-38-3,
106-42-3
138
6.5
106.2
106
91
Compound
CAS No.
BP (C)
Vapor pressure (mmHg)a
MWb
Characteristic
Ion(s)
Primary
Secondary
Styrene
100-42-5
145
6.6
104
104
78
o-Xylene
95-47-6
144
5.0
106.2
106
91
p-Dichlorobenzene
106-46-7
173
0.60
147
146
111, 148
a Pressure in millimeters of mercury. b Molecular weight.
11.0 Analytical Procedure
11.1 Preparation for Sample Analysis.
11.1.1 Each sequence of analyses must be ordered as
follows:
11.1.1.1 CCV.
11.1.1.2 A laboratory blank.
11.1.1.3 Field blank.
11.1.1.4 Sample(s).
11.1.1.5 Field blank.
11.1.1.6 CCV after 10 field samples.
11.1.1.7 CCV at the end of the sample batch.
11.2 Pre-desorption System Checks and Procedures.
11.2.1 Ensure all sample tubes and field blanks are at
ambient temperature before removing them from the storage
container.
11.2.2 If using an automated TD/GC/MS analyzer, remove the
long-term storage caps from the tubes, replace them with
appropriate analytical caps, and load them into the system in
the sequence described in Section 11.1. Alternatively, if using
a manual system, uncap and analyze each tube, one at a time, in
the sequence described in Section 11.1.
11.2.3 The following thermal desorption system integrity
checks and procedures are required before each tube is analyzed.
Note: Commercial thermal desorbers should implement these steps automatically.
11.2.3.1 Tube leak test: Each tube must be leak tested as
soon as it is loaded into the carrier gas flow path before
analysis to ensure data integrity.
11.2.3.2 Conduct the leak test at the GC carrier gas
pressure, without heat or gas flow applied. Tubes that fail the
leak test should not be analyzed, but should be resealed and
stored intact. On automated systems, the instrument should
continue to leak test and analyze subsequent tubes after a given
tube has failed. Automated systems must also store and record
which tubes in a sequence have failed the leak test. Information
on failed tubes should be downloaded with the batch of sequence
information from the analytical system.
11.2.3.3 Leak test the sample flow path. Leak check the
sample flow path of the thermal desorber before each analysis
without heat or gas flow applied to the sample tube. Stop the
automatic sequence of tube desorption and GC analysis if any
leak is detected in the main sample flow path. This process may
be carried out as a separate step or as part of Section
11.2.3.2.
11.2.4 Optional dry purge.
11.2.4.1 Tubes may be dry purged with a flow of pure dry
gas passing into the tube from the sampling end, to remove water
vapor and other very volatile interferents if required.
11.2.5 Internal standard (IS) addition.
11.2.5.1 Use the internal standard addition function of
the automated thermal desorber (if available) to introduce a
precise aliquot of the internal standard to the sampling end of
each tube after the leak test and shortly before primary (tube)
desorption).
Note: This step can be combined with dry purging the tube (Section 11.2.4) if required.
11.2.5.2 If the analyzer does not have a facility for
automatic IS addition, gas or liquid internal standard can be
manually introduced to the sampling end of tubes in a flow of
carrier gas using the types of procedure described in Sections
10.3 and 10.4, respectively.
11.2.6 Pre-purge. Each tube should be purged to vent with
carrier gas flowing in the desorption direction (i.e., flowing
into the tube from the non-sampling end) to remove oxygen before
heat is applied. This is to prevent analyte and sorbent
oxidation and to prevent deterioration of key analyzer
components such as the GC column and mass spectrometer (if
applicable). A series of schematics illustrating these steps is
presented in Figures 17.2 and 17.3.
11.3 Analytical Procedure.
11.3.1 Steps Required for Thermal Desorption.
11.3.1.1 Ensure that the pressure and purity of purge and
carrier gases supplying the TD/GC/MS system, meet manufacturer
specifications and the requirements of this method.
11.3.1.2 Ensure also that the analytical method selected
meets the QC requirements of this method (Section 9) and that
all the analytical parameters are at set point.
11.3.1.3 Conduct predesorption system checks (see Section
11.2).
11.3.1.4 Desorb the sorbent tube under conditions
demonstrated to achieve >95 percent recovery of target compounds
(see Section 9.5.2).
Note: Typical tube desorption conditions range from 280-350 C for 5-15 minutes with a carrier gas flow of 30-100 mL/min
passing through the tube from the non-sampling end such that
analytes are flushed out of the tube from the sampling end.
Desorbed VOCs are concentrated (refocused) on a secondary,
cooled sorbent trap integrated into the analytical equipment
(see Figure 17.4). The focusing trap is typically maintained at
a temperature between -30 and +30 °C during focusing. Selection
of hydrophobic sorbents for focusing and setting a trapping
temperature of +25 to 27 °C aid analysis of humid samples
because these settings allow selective elimination of any
residual water from the system, prior to GC/MS analysis.
Note: The transfer of analytes from the tube to the focusing trap during primary (tube) desorption can be carried out splitless or under controlled split conditions (see Figure 17.4) depending on the masses of target compounds sampled and the requirements of the system—sensitivity, required calibration range, column overload limitations, etc. Instrument controlled sample splits must be demonstrated by showing the reproducibility using calibration standards. Field and laboratory blank samples must be analyzed at the same split as the lowest calibration standard. During secondary (trap) desorption the focusing trap is heated rapidly (typically at rates > 40 °C/s) with inert (carrier) gas flowing through the trap (3-100 mL/min) in the reverse direction to that used during focusing.
11.3.1.5 The split conditions selected for optimum field
sample analysis must also be demonstrated on representative
standards.
Note: Typical trap desorption temperatures are in the range 250-360 C, with a “hold” time of 1-3 minutes at the highest temperature. Trap desorption automatically triggers the start of
GC analysis. The trap desorption can also be carried out under
splitless conditions (i.e., with everything desorbed from the
trap being transferred to the analytical column and GC detector)
or, more commonly, under controlled split conditions (see Figure
17.4). The selected split ratio depends on the masses of target
compounds sampled and the requirements of the system—
sensitivity, required calibration range, column overload
limitations, etc. If a split is selected during both primary
(trap) desorption and secondary (trap) desorption, the overall
split ratio is the product of the two. Such ‘double’ split
capability gives optimum flexibility for accommodating
concentrated samples as well as trace-level samples on the
TD/GC/MS analytical system. High resolution capillary columns
and most GC/MS detectors tend to work best with approximately
20-200 ng per compound per tube to avoid saturation. The overall
split ratio must be adjusted such that, when it is applied to
the sample mass that is expected to be collected during field
monitoring, the amount reaching the column will be attenuated to
fall within this range. As a rule of thumb this means that ~20
ng samples will require splitless or very low split analysis, ~2
μg samples will require a split ratio in the order of ~50:1 and
200 μg samples will require a double split method with an
overall split ratio in the order of 2,000:1.
11.3.1.6 Analyzed tubes must be resealed with long-term
storage caps immediately after analysis (manual systems) or
after completion of a sequence (automated systems). This
prevents contamination, minimizing the extent of tube
reconditioning required before subsequent reuse.
11.3.2 GC/MS Analytical Procedure.
11.3.2.1 Heat/cool the GC oven to its starting set point.
11.3.2.2 If using a GC/MS system, it can be operated in
either MS-Scan or MS-SIM mode (depending on required sensitivity
levels and the type of mass spectrometer selected). As soon as
trap desorption and transfer of analytes into the GC column
triggers the start of the GC/MS analysis, collect mass spectral
data over a range of masses from 35 to 300 amu. Collect at least
10 data points per eluting chromatographic peak in order to
adequately integrate and quantify target compounds.
11.3.2.3 Use secondary ion quantitation only when there
are sample matrix interferences with the primary ion. If
secondary ion quantitation is performed, flag the data and
document the reasons for the alternative quantitation procedure.
11.3.2.4 Data reduction is performed by the instruments
post processing program that is automatically accessed after
data acquisition is completed at the end of the GC run. The
concentration of each target compound is calculated using the
previously established response factors for the CCV analyzed in
Section 11.1.1.6.
11.3.2.5 Whenever the thermal desorption - GC/MS analytical
method is changed or major equipment maintenance is performed,
you must conduct a new five-level calibration (see Section
10.6.3). System calibration remains valid as long as results
from subsequent CCV are within 30 percent of the most recent 5-
point calibration (see Section 10.9.5). Include relevant CCV
data in the supporting information in the data report for each
set of samples.
11.3.2.6 Document, flag and explain all sample results
that exceed the calibration range. Report flags and provide
documentation in the analytical results for the affected
sample(s).
12.0 Data Analysis, Calculations, and Reporting
12.1 Recordkeeping Procedures for Sorbent Tubes.
12.1.1 Label sample tubes with a unique identification
number as described in Section 6.3.
12.1.2 Keep records of the tube numbers and sorbent lots
used for each sampling period.
12.1.3 Keep records of sorbent tube packing if tubes are
manually prepared in the laboratory and not supplied
commercially. These records must include the masses and/or bed
lengths of sorbent(s) contained in each tube, the maximum
allowable temperature for that tube and the date each tube was
packed. If a tube is repacked at any stage, record the date of
tube repacking and any other relevant information required in
Section 12.1.
12.1.4 Keep records of the conditioning and blanking of
tubes. These records must include, but are not limited to, the
unique identification number and measured background resulting
from the tube conditioning.
12.1.5 Record the location, dates, tube identification and
times associated with each sample collection. Record this
information on a Chain of Custody form that is sent to the
analytical laboratory.
12.1.6 Field sampling personnel must complete and send a
Chain of Custody to the analysis laboratory (see Section 8.6.4
of Method 325A for what information to include and Section 17.0
of this method for an example form). Duplicate copies of the
Chain of Custody must be included with the sample report and
stored with the field test data archive.
12.1.7 Field sampling personnel must also keep records of
the unit vector wind direction, sigma theta, temperature and
barometric pressure averages for the sampling period. See
Section 8.3.4 of Method 325A.
12.1.8 Laboratory personnel must record the sample receipt
date, and analysis date.
12.1.9 Laboratory personnel must maintain records of the
analytical method and sample results in electronic or hardcopy
in sufficient detail to reconstruct the calibration, sample, and
quality control results from each sampling period.
12.2 Calculations.
12.2.1 Complete the calculations in this section to
determine compliance with calibration quality control criteria
(see also Table 17.1).
12.2.1.1 Response factor (RF). Calculate the RF using
Equation 12.1:
Where: As = Ais =
Ms =
RF As M is Eq. 12.1 Ais Ms
Peak area for the characteristic ion of the analyte.
Peak area for the characteristic ion of the internal
standard.
Mass of the analyte.
Mass of the internal standard.
12.2.1.2 Standard deviation of the response factors (SDRF).
Mis =
Calculate the SDRF using Equation 12.2:
Where: RFi =
RF = n =
Mean RF for each compound from the initial calibration.
Number of calibration standards.
n RFRF i
SD i1 n1 RF
RF for each of the calibration compounds.
2
Eq.12.2
12.2.1.3 Percent deviation (%DEV). Calculate the %DEV
using Equation 12.3:
%DEVSDRF RF100 Eq.12.3 SDRF = Standard deviation.
RF = Mean RF for each compound from the initial calibration. 12.2.1.4 Relative percent difference (RPD). Calculate the
Where:
RPD using Equation 12.4:
RPD R1R2 100 R1R2/2
Eq. 12.4
Where: R1, R2
= Values that are being compared (i.e., response factors in CCV).
12.2.2 Determine the equivalent concentration of compounds
in atmospheres as follows.
12.2.3 Correct target concentrations determined at the
sampling site temperature and atmospheric pressure to standard
conditions (25 C and 760 mm mercury) using Equation 12.5 (Reference 21).
3 298.22 P
UNTP U ss tss 760
Eq.12.5
Where:
tss = The average temperature during the collection period at the sampling site (K).
Pss = The average pressure at the sampling site during the collection period (mm Hg).
U = The diffusive uptake rate (sampling rate) (mL/min). 12.2.4 For passive sorbent tube samples, calculate the
concentration of the target compound(s) in the sampled air, in μg/m3 by using Equation 12.6 (Reference 22).
Where: Cm =
mmeas =
UNTP =
The concentration of target compound in the air sampled (μg/m3).
The mass of the compound as measured in the sorbent tube
(μg).
The diffusive uptake rate corrected for local conditions
(sampling rate) (mL/min).
C
m
mmeas 106 Eq. 12.6 UNTP t
t =
Note: Diffusive uptake rates for common VOCs, using carbon
sorbents packed into sorbent tubes of the dimensions specified
in Section 6.1, are listed in Table 12.1. Adjust analytical
conditions to keep expected sampled masses within range (see
Sections 11.3.1.3 to 11.3.1.5). Best possible method detection
limits are typically in the order of 0.1 ppb for 1,3-butadiene
and 0.05 ppb for volatile aromatics such as benzene for 14-day
monitoring. However, actual detection limits will depend upon
the analytical conditions selected.
Table 12.1: Validated Sorbents and Uptake Rates (mL/min) for
Selected Clean Air Act Compounds
The exposure time (minutes).
Compound
CarbopackTM Xa
CarbographTM 1 TD
CarbopackTM B
1,1-Dichloroethene
0.57±0.14
not available
not available
3-Chloropropene
0.51±0.3
not available
not available
1,1-Dichloroethane
0.57±0.1
not available
not available
1,2-Dichloroethane
0.57±0.08
not available
not available
1,1,1-Trichloroethane
0.51±0.1
not available
not available
Benzene
0.67±0.06
0.63±0.07b
0.63±0.07b
Carbon tetrachloride
0.51±0.06
not available
not available
1,2-Dichloropropane
0.52±0.1
not available
not available
Trichloroethene
0.5±0.05
not available
not available
1,1,2-Trichloroethane
0.49±0.13
not available
not available
Toluene
0.52±0.14
0.56±0.06c
0.56±0.06c
Tetrachloroethene
0.48±0.05
not available
not available
Chlorobenzene
0.51±0.06
not available
not available
Ethylbenzene
0.46±0.07
not available
0.50c
m,p-Xylene
0.46±0.09
0.47±0.04c
0.47±0.04c
Styrene
0.5±0.14
not available
not available
o-Xylene
0.46±0.12
0.47±0.04c
0.47±0.04c
p-Dichlorobenzene
0.45±0.05
not available
not available
a Reference 3, McClenny, J. Environ. Monit. 7:248-256. Based on 24-hour duration.
b Reference 24, BS EN 14662-4:2005 (incorporated by reference-see §63.14). Based on 14-day duration.
c Reference 25, ISO 16017-2:2003(E) (incorporated by reference-see §63.14). Based on 14-day duration.
13.0 Method Performance
The performance of this procedure for VOC not listed in
Table 12.1 is determined using the procedure in Addendum A of
this Method or by one of the following national/international
standard methods: ISO 16017-2:2003(E), ASTM D6196-03 (Reapproved
2009), or BS EN 14662-4:2005 (all incorporated by reference-see
§63.14).
13.1 The valid range for measurement of VOC is approximately 0.5 μg/m3 to 5 mg/m3 in air, collected over a 14-
day sampling period. The upper limit of the useful range depends
on the split ratio selected (Section 11.3.1) and the dynamic
range of the analytical system. The lower limit of the useful
range depends on the noise from the analytical instrument
detector and on the blank level of target compounds or
interfering compounds on the sorbent tube (see Section 13.3).
13.2 Diffusive sorbent tubes compatible with passive
sampling and thermal desorption methods have been evaluated at
relatively high atmospheric concentrations (i.e., mid-ppb to
ppm) and published for use in workplace air and
industrial/mobile source emissions (References 15-16, 21-22).
13.3 Best possible detection limits and maximum quantifiable concentrations of air pollutants range from sub- part-per-trillion (sub-ppt) for halogenated species such as CCl4 and the freons using an electron capture detector (ECD), SIM Mode GC/MS, triple quad MS or GC/TOF MS to sub-ppb for volatile hydrocarbons collected over 72 hours followed by analysis using GC with quadrupole MS operated in the full SCAN mode.
13.3.1 Actual detection limits for atmospheric monitoring
vary depending on several key factors. These factors are:
• Minimum artifact levels.
• GC detector selection.
• Time of exposure for passive sorbent tubes.
• Selected analytical conditions, particularly column resolution and split ratio.
14.0 Pollution Prevention
This method involves the use of ambient concentrations of
gaseous compounds that post little or no danger of pollution to
the environment.
15.0 Waste Management
Dispose of expired calibration solutions as hazardous
materials. Exercise standard laboratory environmental practices
to minimize the use and disposal of laboratory solvents.
16.0 References
1. Winberry, W. T. Jr., et al., Determination of Volatile
Organic Compounds in Ambient Air Using Active Sampling onto
Sorbent Tubes: Method TO-17r, Second Edition, U.S. Environmental
Protection Agency, Research Triangle Park, NC 27711, January
1999. https://www.epa.gov/ttnamti1/airtox.html#compendium
2. Ciccioli, P., Brancaleoni, E., Cecinato, A.,
Sparapini, R., and Frattoni, M., "Identification and
Determination of Biogenic and Anthropogenic VOCs in Forest Areas
of Northern and Southern Europe and a Remote Site of the
Himalaya Region by High-resolution GC-MS," J. of Chrom., 643, pp
55-69, 1993.
3. McClenny, W.A., K.D. Oliver, H.H. Jacumin, Jr., E.H.
Daughtrey, Jr., D.A. Whitaker. 2005. 24 h diffusive sampling of
toxic VOCs in air onto CarbopackTM X solid adsorbent followed by thermal desorption/GC/MS analysis– laboratory studies. J. Environ. Monit. 7:248-256.
4. Markes International (www.markes.com/publications):
Thermal desorption Technical Support Note 2: Prediction of
uptake rates for diffusive tubes.
5. Ciccioli, P., Brancaleoni, E., Cecinato, A., DiPalo,
C., Brachetti, A., and Liberti, A., "GC Evaluation of the
Organic Components Present in the Atmosphere at Trace Levels
with the Aid of CarbopackTM B for Preconcentration of the
Sample," J. of Chrom., 351, pp 433-449, 1986.
6. Broadway, G. M., and Trewern, T., "Design
Considerations for the Optimization of a Packed Thermal
Desorption Cold Trap for Capillary Gas Chromatography," Proc.
13th Int’l Symposium on Capil. Chrom., Baltimore, MD, pp 310-
320, 1991.
7. Broadway, G. M., "An Automated System for use Without
Liquid Cryogen for the Determination of VOC’s in Ambient Air,"
Proc. 14th Int’l. Symposium on Capil. Chrom., Baltimore, MD,
1992.
8. Gibitch, J., Ogle, L., and Radenheimer, P., "Analysis
of Ozone Precursor Compounds in Houston, Texas Using Automated
Continuous GCs," in Proceedings of the Air and Waste Management
Association Conference: Measurement of Toxic and Related Air
Pollutants, Air and Waste Management Association, Pittsburgh,
PA, May 1995.
9. Vandendriessche, S., and Griepink, B., "The Certification of Benzene, Toluene and m-Xylene Sorbed on Tenax® TA in Tubes," CRM-112 CEC, BCR, EUR12308 EN, 1989.
10. MDHS 2 (Acrylonitrile in Air), "Laboratory Method
Using Porous Polymer Adsorption Tubes, and Thermal Desorption
with Gas Chromatographic Analysis," Methods for the
Determination of Hazardous Substances (MDHS), UK Health and
Safety Executive, Sheffield, UK.
11. MDHS 22 (Benzene in Air), "Laboratory Method Using
Porous Polymer Adsorbent Tubes, Thermal Desorption and Gas
Chromatography," Method for the Determination of Hazardous
Substances (MDHS), UK Health and Safety Executive, Sheffield,
UK.
12. MDHS 23 (Glycol Ether and Glycol Acetate Vapors in Air), "Laboratory Method Using Tenax® Sorbent Tubes, Thermal Desorption and Gas Chromatography," Method for the Determination of Hazardous Substances (MDHS), UK Health and Safety Executive, Sheffield, UK.
13. MDHS 40 (Toluene in air), "Laboratory Method Using
Pumped Porous Polymer Adsorbent Tubes, Thermal Desorption and
Gas Chromatography," Method for the Determination of Hazardous
Substances (MDHS), UK Health and Safety Executive, Sheffield,
UK.
14. MDHS 60 (Mixed Hydrocarbons (C to C) in Air),
"Laboratory Method Using Pumped Porous Polymer 3 10 and Carbon
Sorbent Tubes, Thermal Desorption and Gas Chromatography,"
Method for the Determination of Hazardous Substances (MDHS), UK
Health and Safety Executive, Sheffield, UK.
15. Price, J. A., and Saunders, K. J., "Determination of
Airborne Methyl tert-Butyl Ether in Gasoline Atmospheres,"
Analyst, Vol. 109, pp. 829-834, July 1984.
16. Coker, D. T., van den Hoed, N., Saunders, K. J., and
Tindle, P. E., "A Monitoring Method for Gasoline Vapour Giving
Detailed Composition," Ann. Occup, Hyg., Vol 33, No. 11, pp 15-
26, 1989.
17. DFG, "Analytische Methoden zur prufing
gesundheitsschadlicher Arbeistsstoffe," Deutsche
Forschungsgemeinschaft, Verlag Chemie, Weinheim FRG, 1985.
18. NNI, "Methods in NVN Series (Luchtkwaliteit;
Werkplekatmasfeer)," Nederlands Normailsatie - Institut, Delft,
The Netherlands, 1986-88.
19. "Sampling by Solid Adsorption Techniques," Standards
Association of Australia Organic Vapours, Australian Standard
2976, 1987.
20. Woolfenden, E. A., "Monitoring VOCs in Air Using
Pumped Sampling onto Sorbent Tubes Followed by Thermal
Desorption-capillary GC Analysis: Summary of Reported Data and
Practical Guidelines for Successful Application," J. Air & Waste
Manage. Assoc., Vol. 47, 1997, pp. 20-36.
21. Validation Guidelines for Air Sampling Methods
Utilizing Chromatographic Analysis, OSHA T-005, Version 3.0, May
2010,
https://www.osha.gov/dts/sltc/methods/chromguide/chromguide.pdf.
22. ASTM D4597-10, Standard Practice for Sampling
Workplace Atmospheres to collect Gases or Vapors with Solid
Sorbent Diffusive Samplers.
23. Martin, https://www.hsl.gov.uk/media/1619/issue14.pdf.
24. BS EN 14662-4:2005, Ambient air quality – Standard
method for the measurement of benzene concentrations – Part 4:
Diffusive sampling followed by thermal desorption and gas
chromatography.
25. ISO 16017-2:2003(E): Indoor, ambient and workplace air
– Sampling and analysis of volatile organic compounds by sorbent
tube/thermal desorption/capillary gas chromatography – Part 2:
Diffusive sampling.
17.0 Tables, Diagrams, Flowcharts and Validation Data
Table 17.1. Summary of GC/MS Analysis Quality Control Procedures
Parameter
Frequency
Acceptance
Criteria
Corrective Action
Bromofluorobenzene
Instrument Tune
Performance Check
Dailya prior to sample analysis
Evaluation
criteria
presented in
1) Retune and or
2) Perform
Maintenance
Section 9.5 and
Table 9.2.
Five point
calibration
bracketing the
expected sample
concentration.
Following any
major change,
repair or
maintenance or if
daily CCV does
not meet method
requirements.
Recalibration not
to exceed three
months.
1) Percent
Deviation (%DEV)
of response
factors ±30%
2) Relative
Retention Times
(RRTs) for target
peaks ±0.06 units
from mean RRT
1) Repeat
calibration
sample analysis
2) Repeat
linearity check
3) Prepare new
calibration
standards as
necessary and
repeat analysis
Calibration
Verification (CCV
Second source
calibration
verification
check)
Following the
calibration curve
The response
factor ±30% DEV
from calibration
curve average
response factor
1) Repeat
calibration check
2) Repeat
calibration curve
Laboratory Blank
Analysis
Dailya following bromofluorobenzen e and calibration check; prior to sample analysis
1) ≤0.2 ppbv per
analyte or ≤ 3
times the LOD,
whichever is
greater
2) Internal
Standard (IS)
area response
±40% and IS
Retention Time
(RT) ±0.33 min.
of most recent
calibration check
1) Repeat
analysis with new
blank tube
2) Check system
for leaks,
contamination
3) Analyze
additional blank
Blank Sorbent Tube
Certification
One tube analyzed
for each batch of
tubes cleaned or
10 percent of
tubes whichever
is greater.
<0.2 ppbv per VOC
targeted compound
or 3 times the
LOD, whichever is
greater
Reclean all tubes
in batch and
reanalyze
Samples - Internal
Standards
All samples
IS area response
±40% and IS RT
±0.33 min. of
most recent
calibration
validation
Flag Data for
possible
invalidation
a Every 24 hours
Method 325 A/B
EXAMPLE FIELD TEST DATA SHEET (FTDS)
AND
CHAIN OF CUSTODY
I. GENERAL INFORMATION
SITE NAME:
_________________________________________________________
SITE LOCATION ADDRESS:
_____________________________________________
CITY: _____________________STATE: _____________ ZIP: __________
II. SAMPLING DATA
Sample
ID
(Tube)
#
Sorbent
Sample
or
blank
Start Date
Start Time
Stop Date
Stop Time
Location
(gps)
Ambient
Temp.
(F)
Barometric
Pressure
(in. Hg)
III. CUSTODY INFORMATION
COLLECTED BY: ___________________
Relinquished to Shipper -
Name: _______________ Date: ________________
Received by Laboratory -
Name _______________ Date: ________________
Sample condition upon receipt:
________________________________________________________________
Analysis Required:
________________________________________________________________
________________________________________________________________
Comments:
________________________________________________________________
________________________________________________________________
________________________________________________________________
Figure 17.1. Example Field Data From and Chain of Custody
Time _________
Time _________
Figure 17.2. Schematic of Thermal Desorption Flow Path During
Leak Testing
Figure 17.3. Schematic of Thermal Desorption Flow During Purge
of Air (Top) and Addition of IS Gas to the Sorbent Tube (Bottom)
Figure 17.4. Schematic of Thermal Desorption Flow Path During
Primary (Tube) Desorption (Top) and Secondary (Trap) Desorption
and Transfer to the GC (Bottom)
ADDENDUM A to Method 325B--Method 325 Performance Evaluation
A.1 Scope and Application
A.1.1 To be measured by Methods 325A and 325B, each new
target volatile organic compound (VOC) or sorbent that is not
listed in Table 12.1 must be evaluated by exposing the selected
sorbent tube to a known concentration of the target compound(s)
in an exposure chamber following the procedure in this Addendum
or by following the procedures in the national/international
standard methods: ISO 16017-2:2003(E), ASTM D6196-03 (Reapproved
2009), or BS EN 14662-4:2005 (all incorporated by reference—see
§63.14), or reported in peer-reviewed open literature.
A.1.2 You must determine the uptake rate and the relative
standard deviation compared to the theoretical concentration of
volatile material in the exposure chamber for each of the tests
required in this method. If data that meet the requirement of
this Addendum are available in the peer reviewed open literature
for VOCs of interest collected on your passive sorbent tube
configuration, then such data may be submitted in lieu of the
testing required in this Addendum.
A.1.3 You must expose sorbent tubes in a test chamber to
parts per trillion by volume (pptv) and low parts per billion by
volume (ppbv) concentrations of VOCs in humid atmospheres to
determine the sorbent tube uptake rate and to confirm compound
capture and recovery.
A.2 Summary of Method
Note: The technique described here is one approach for
determining uptake rates for new sorbent/sorbate pairs. It is
equally valid to follow the techniques described in any one of
the following national/international standards methods: ISO
16017-2:2003(E), ASTM D6196-03 (Reapproved 2009), or BS EN
14662-4:2005 (all incorporated by reference-see §63.14).
A.2.1 Known concentrations of VOC are metered into an
exposure chamber containing sorbent tubes filled with media
selected to capture the volatile organic compounds of interest
(see Figure A.1 and A.2 for an example of the exposure chamber
and sorbent tube retaining rack). VOC are diluted with humid air
and the chamber is allowed to equilibrate for 6 hours. Clean
passive sampling devices are placed into the chamber and exposed
for a measured period of time. The passive uptake rate of the
passive sampling devices is determined using the standard and
dilution gas flow rates. Chamber concentrations are confirmed
with whole gas sample collection and analysis or direct
interface volatile organic compound measurement methods.
A.2.2 An exposure chamber and known gas concentrations
must be used to challenge and evaluate the collection and
recovery of target compounds from the sorbent and tube selected
to perform passive measurements of VOC in atmospheres.
A.3 Definitions
A.3.1 cc is cubic centimeter.
A.3.2 ECD is electron capture detector.
A.3.3 FID is flame ionization detector.
A.3.4 LED is light-emitting diode.
A.3.5 MFC is mass flow controller.
A.3.6 MFM is mass flow meter.
A.3.7 min is minute.
A.3.8 ppbv is parts per billion by volume.
A.3.9 ppmv is parts per million by volume.
A.3.10 PSD is passive sampling device.
A.3.11 psig is pounds per square inch gauge.
A.3.12 RH is relative humidity.
A.3.13 VOC is volatile organic compound.
A.4 Interferences
A.4.1 VOC contaminants in water can contribute
interference or bias results high. Use only distilled, organic-
free water for dilution gas humidification.
A.4.2 Solvents and other VOC-containing liquids can
contaminate the exposure chamber. Store and use solvents and
other VOC-containing liquids in the exhaust hood when exposure
experiments are in progress to prevent the possibility of
contamination of VOCs into the chamber through the chamber’s
exhaust vent.
Note: Whenever possible, passive sorbent evaluation should
be performed in a VOC free laboratory.
A.4.3 PSDs should be handled by personnel wearing only
clean, white cotton or powder free nitrile gloves to prevent
contamination of the PSDs with oils from the hands.
A.4.4 This performance evaluation procedure is applicable
to only volatile materials that can be measured accurately with
direct interface gas chromatography or whole gas sample
collection, concentration and analysis. Alternative methods to
confirm the concentration of volatile materials in exposure
chambers are subject to Administrator approval.
A.5 Safety
A.5.1 This procedure does not address all of the safety
concerns associated with its use. It is the responsibility of
the user of this standard to establish appropriate field and
laboratory safety and health practices and determine the
applicability of regulatory limitations prior to use.
A.5.2 Laboratory analysts must exercise appropriate care
in working with high-pressure gas cylinders.
A.6 Equipment and Supplies
A.6.1 You must use an exposure chamber of sufficient size
to simultaneously expose a minimum of eight sorbent tubes.
A.6.2 Your exposure chamber must not contain VOC that
interfere with the compound under evaluation. Chambers made of
glass and/or stainless steel have been used successfully for
measurement of known concentration of selected VOC compounds.
A.6.3 The following equipment and supplies are needed:
Clean, white cotton or nitrile gloves;
Conditioned passive sampling device tubes and diffusion
caps; and
NIST traceable high resolution digital gas mass flow meters (MFMs) or flow controllers (MFCs).
A.7 Reagents and Standards
A.7.1 You must generate an exposure gas that contains
between 35 and 75 percent relative humidity and a concentration
of target compound(s) within 2 to 5 times the concentration to
be measured in the field.
A.7.2 Target gas concentrations must be generated with
certified gas standards and diluted with humid clean air.
Dilution to reach the desired concentration must be done with
zero grade air or better.
A.7.3 The following reagents and standards are needed:
Distilled water for the humidification;
VOC standards mixtures in high-pressure cylinder certified by the supplier (Note: The accuracy of the certified standards has a direct bearing on the accuracy of the measurement results. Typical vendor accuracy is ±5
percent accuracy but some VOC may only be available at
lower accuracy (e.g., acrolein at 10 percent)); and
• Purified dilution air containing less than 0.2 ppbv of the target VOC.
A.8 Sample Collection, Preservation and Storage
A.8.1 You must use certified gas standards diluted with
humid air. Generate humidified air by adding distilled organic
free water to purified or zero grade air. Humidification may be
accomplished by quantitative addition of water to the air
dilution gas stream in a heated chamber or by passing purified
air through a humidifying bubbler. You must control the relative
humidity in the test gas throughout the period of passive
sampler exposure.
Note: The RH in the exposure chamber is directly proportional to the fraction of the purified air that passes through the water in the bubbler before entering the exposure chamber. Achieving uniform humidification in the proper range is a trial-and-error process with a humidifying bubbler. You may need to heat the bubbler to achieve sufficient humidity. An equilibration period of approximately 15 minutes is required following each adjustment of the air flow through the humidifier. Several adjustments or equilibration cycles may be required to achieve the desired RH level.
Note: You will need to determine both the dilution rate and
the humidification rate for your design of the exposure chamber
by trial and error before performing method evaluation tests.
A.8.2 Prepare and condition sorbent tubes following the
procedures in Method 325B Section 7.0.
A.8.3 You must verify that the exposure chamber does not
leak.
A.8.4 You must complete two evaluation tests using a
minimum of eight passive sampling tubes in each test with less
than 5-percent depletion of test analyte by the samplers.
A.8.4.1 Perform at least one evaluation at two to five
times the estimated analytical detection limit or less.
A.8.4.2 Perform second evaluation at a concentration
equivalent to the middle of the analysis calibration range.
A.8.5 You must evaluate the samplers in the test chamber
operating between 35 percent and 75 percent RH, and at 25 ±5 °C.
Allow the exposure chamber to equilibrate for 6 hours before
starting an evaluation.
A.8.6 The flow rate through the chamber must be ≤ 0.5
meter per second face velocity across the sampler face.
A.8.7 Place clean, ready to use sorbent tubes into the
exposure chamber for predetermined amounts of time to evaluate
collection and recovery from the tubes. The exposure time
depends on the concentration of volatile test material in the
chamber and the detection limit required for the sorbent tube
sampling application. Exposure time should match sample
collection time. The sorbent tube exposure chamber time may not
be less than 24 hours and should not be longer than 2 weeks.
A.8.7.1 To start the exposure, place the clean PSDs
equipped with diffusion caps on the tube inlet into a retaining
rack.
A.8.7.2 Place the entire retaining rack inside the
exposure chamber with the diffusive sampling end of the tubes
facing into the chamber flow. Seal the chamber and record the
exposure start time, chamber RH, chamber temperature, PSD types
and numbers, orientation of PSDs, and volatile material mixture
composition (see Figure A.2).
A.8.7.3 Diluted, humidified target gas must be
continuously fed into the exposure chamber during cartridge
exposure. Measure the flow rate of target compound standard gas
and dilution air to an accuracy of 5 percent.
A.8.7.4 Record the time, temperature, and RH at the
beginning, middle, and end of the exposure time.
A.8.7.5 At the end of the exposure time, remove the PSDs
from the exposure chamber. Record the exposure end time, chamber
RH, and temperature.
Figure A.1. Example Sorbent Tube Exposure Chamber
Figure A.2. Example Tube Retaining Rack in Exposure Chamber
A.9 Quality Control
A.9.1 Monitor and record the exposure chamber temperature
and RH during PSD exposures.
A.9.2 Measure the flow rates of standards and purified
humified air immediately following PSD exposures.
A.10 Calibration and Standardization
A.10.1 Follow the procedures described in Method 325B
Section 10.0 for calibration.
A.10.2 Verify chamber concentration by direct injection
into a gas chromatograph calibrated for the target compound(s)
or by collection of an integrated SUMMA canister followed by
analysis using a preconcentration gas chromatographic method
such as EPA Compendium Method TO–15, Determination of VOCs in
Air Collected in Specially-Prepared Canisters and Analyzed By
GC/MS.
A.10.2.1 To use direct injection gas chromatography to
verify the exposure chamber concentration, follow the procedures
in Method 18 of 40 CFR part 60, Appendix A-6. The method ASTM
D6420-99 (Reapproved 2010) (incorporated by reference—see
§63.14) is an acceptable alternative to EPA Method 18 of 40 CFR
part 60).
Note: Direct injection gas chromatography may not be sufficiently sensitive for all compounds. Therefore, the whole gas preconcentration sample and analysis method may be required to measure at low concentrations.
A.10.2.2 To verify exposure chamber concentrations using
SUMMA canisters, prepare clean canister(s) and measure the
concentration of VOC collected in an integrated SUMMA canister
over the period used for the evaluation (minimum 24 hours).
Analyze the TO-15 canister sample following EPA Compendium
Method TO-15.
A.10.2.3 Compare the theoretical concentration of volatile
material added to the test chamber to the measured concentration
to confirm the chamber operation. Theoretical concentration must
agree with the measured concentration within 30 percent.
A.11 Analysis Procedure
Analyze the sorbent tubes following the procedures
described in Section 11.0 of Method 325B.
A.12 Recordkeeping Procedures for Sorbent Tube Evaluation
Keep records for the sorbent tube evaluation to include at
a minimum the following information:
A.12.1 Sorbent tube description and specifications.
A.12.2 Sorbent material description and specifications.
A.12.3 Volatile analytes used in the sampler test.
A.12.4 Chamber conditions including flow rate,
temperature, and relative humidity.
A.12.5 Relative standard deviation of the sampler results
at the conditions tested.
A.12.6 95 percent confidence limit on the sampler overall
accuracy.
A.12.7 The relative accuracy of the sorbent tube results
compared to the direct chamber measurement by direct gas
chromatography or SUMMA canister analysis.
A.13 Method Performance
A.13.1 Sorbent tube performance is acceptable if the
relative accuracy of the passive sorbent sampler agrees with the
active measurement method by ±10 percent at the 95 percent
confidence limit and the uptake ratio is equal to greater than
0.5 mL/min (1 ng/ppm-min).
Note: For example, there is a maximum deviation comparing Perkin-Elmer passive type sorbent tubes packed with CarbopackTM X of 1.3 to 10 percent compared to active sampling using the following uptake rates.
a McClenny, W.A., K.D. Oliver, H.H. Jacumin, Jr., E.H. Daughtrey, Jr., D.A. Whitaker. 2005. 24 h diffusive sampling of toxic VOCs in air onto CarbopackTM X solid adsorbent followed by thermal desorption/GC/MS analysis– laboratory studies. J. Environ. Monit. 7:248-256.
A.13.2 Data Analysis and Calculations for Method
Evaluation
A.13.2.1 Calculate the theoretical concentration of VOC
standards using Equation A.1.
Where:
1,3-butadiene
uptake rate
mL/min
Estimated
Detection
Limit
(2 week)
Benzene
uptake rates
mL/min
Estimated
Detection
Limit
(2 week)
CarbopackTM X (2 week)
0.61±0.11a
0.1 ppbv
0.67a
0.05 ppbv
C FRi C Eq.A.1
f FRFR s ta
Cf =
FRi = FRt =
FRa = Cs =
The final concentration of standard in the exposure
chamber (ppbv).
The flow rate of the target compound I (mL/min).
The flow rate of all target compounds from separate if
multiple cylinders are used (mL/min).
The flow rate of dilution air plus moisture (mL/min).
The concentration of target compound in the standard
cylinder (parts per million by volume).
A.13.2.3 Determine the uptake rate of the target gas being
evaluated using Equation A.2.
U Mx Ce Tt
Eq. A.2
Where: Mx =
Ce = Tt =
deviation (RSD)) of the inter-sampler results at each condition
tested using Equation A.3. RSD for the sampler is estimated by
pooling the variance estimates from each test run.
The mass of analyte measured on the sampling tube (g).
The theoretical exposure chamber concentration (g/mL).
The exposure time (minutes).
A.13.2.4 Estimate the variance (relative standard
X X S2 in1
i
n
2
Eq.A.3
Where: Xi =
Xi =
The measured mass of analyte found on sorbent tube i. ThemeanvalueofallXi.
n = The number of measurements of the analyte.
A.13.2.4 Determine the percent relative standard deviation
of the inter-sampler results using Equation A.4.
%RSD 100 S2
x X Eq. A.4
A.13.2.5 Determine the 95 percent confidence interval for
the sampler results using Equation A.5. The confidence interval
is determined based on the number of test runs performed to
evaluate the sorbent tube and sorbent combination. For the
minimum test requirement of eight samplers tested at two
concentrations, the number of tests is 16 and the degrees of
freedom are 15.
Where:
%RSD = t0.95 =
95%
%RSDt0.95 f
95% n Eq. A.5
= 95 percent confidence interval.
percent relative standard deviation.
The Students t statistic for f degrees of freedom at 95
percent confidence.
f =
n = Number of samples.
The number of degrees of freedom.
A.13.2.6 Determine the relative accuracy of the sorbent
tube combination compared to the active sampling results using
Equation A.6.
Where:
RAXi XA 95%
= Relative accuracy.
=ThemeanvalueofallXi.
Eq. A.6
RA
X i XA
This method involves the use of ambient concentrations of
gaseous compounds that post little or no pollution to the
environment.
A.15 Waste Management
Expired calibration solutions should be disposed of as
hazardous materials.
A.16 References
1. ISO TC 146/SC 02 N 361 Workplace atmospheres –
Protocol for evaluating the performance of diffusive samplers.
= The average concentration of analyte measured by the active measurement method.
= 95 percent confidence interval.
A.14 Pollution Prevention
95%