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Method 325B—Volatile Organic Compounds from Fugitive and Area

               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
( (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

   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

    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

   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

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

   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

    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

    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

   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

   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

   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

   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

   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)



Carrier Gas Flow

Carbotrap C CarbopackTM C Anasorb GCB2 CarbographTM 1 TD Carbotrap CarbopackTM B Anasorb GCB1



100 mL/min

Tenax TA CarbopackTM X



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

   9.5  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


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.


  • 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


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

   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 %