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800-356-1688
I. Introduction
Ambient air sampling involves collectinga representative sampleof ambient air
for analysis. There are two general approaches: 1) “whole air” sampling with
canisters or Tedlar® bags and 2) “in-field concentration” sampling using sor-
bent tubes or cold traps. In this guide, we focus on collectingwhole air sam-
ples in canisters, a flexible techniquewithmany applications (Table I).
Passivevs.ActiveSampling
In canister sampling, two sampling techniques are commonly used: passive
sampling and active sampling.Active sampling requires the use of a pumping
devicewhereas passive samplingdoes not.
In passive sampling, an air sample is pulled through a flow controller into an
evacuated canister over a chosenperiodof time, ranging from 5minutes to 24
hours. The sampling period and the flow rate determine the canister volume
required. Inactive sampling, apump isused topush the sample throughamass
flowcontrollerand into thecanister.Additional samplecanbecollected, relative
to theamount thatcanbecollectedbypassivesampling,bypressurizing thecan-
ister with sample. Commonly the sample is pressurized to 15 psig, effectively
doubling the sample volume.
Although active sampling is very flexible, a drawback to using a pump is the
need for additional qualityassurance requirements for sample integrity (i.e.,no
artifacts or loss of analytes). Additionally, a pump requires a battery or line
power source,whichmaybedifficult in remote field-site sampling.
Grabvs. IntegratedSampling
If the environment is not changing, or if only a qualitative sample is needed, a
simple“grab”samplecanbeobtained.For example, anevacuated samplecanis-
ter canbeopened and sample rapidly collected at anuncontrolled rate, usually
over several seconds, until the container reaches equilibriumwith atmospheric
pressure. Generally this qualitative approach is used when unknown analytes
mustbe identified,when theair containshighconcentrationsof analytes at cer-
tain (short) times, orwhen an odor is noticed and a samplemust be obtained
quickly.Pairedgrab samples(before/afteror smell/no smell)oftenareemployed
toqualitativelydiagnose aperceivedproblem.
To obtain amore representative sample requires time-integrated sampling. A
flow restrictor is used to spread the sample collection flowover a specific time
period to ensure an “average” composited or time-weighted average (TWA)
sample. A TWA sample will accurately reflect the mean conditions of the
ambient air in theenvironment and ispreferredwhen, for regulatoryorhealth
reasons, a typical exposure concentration is required for a situation thatmay
have high variability, as in anoccupational setting.
II.EquipmentUsed forPassiveAirSampling
To ensure a valid samplewhenusing apassive sampling technique, it is impor-
tant that the flow rate not change greatly during the time interval specified for
the integrated sample. The proper sampling equipment helps accomplish this
objective.A typical passive sampling train should include the followingcompo-
nents, all constructedof stainless steel: a sampling inlet, a sinteredmetal parti-
cle filter, a critical orifice, a flow controllingdevice, avacuumgauge, and a can-
ister (Figures 1 and2).
Figure2
Integratedsamplingkit.
sampling inlet
sample
canister
vacuum
gauge
filter
flow
controller
critical
orifice
rain cap
(
1
/
8
" or
1
/
4
" nut)
Figure1
Canister grab samplingkit.
Table I
Canister applications.
Methods
US EPATO-14A,TO-15; ASTMD5466
OSHAPV2120; NIOSHProtocol Draft
Sampling Environment
Ambient air, indoor air, vapor intrusion, emergency response
VOCRange
<C3 to~C10
Sampling Type
Grab& integrated sampling
Sensitivity
ppt to ppm
Sample
inlet
Fitting
with
orifice
10μm
Frit
Unassembled
kit components
Assembled
kitoncanister
Website :
E-mail :
TelNo : 03 9762 2034 . . . inAUSTRALIA
