Phone: 800-356-1688 or 814-353-1300
2
dependable
execution
One of our standing goals is to provide youwith practical
information to help you obtain reliable data from your
chromatographic and peripheral systems.This guide describes
equipment needed and practical techniques to followwhen
collecting passive air samples, using canisters. It is a
compilation of information based on our experience and that of
experts in this field.Wewould like to thank the individualswho
provided invaluable assistance in the development of this guide:
Dr. EricWinegar of AppliedMeasurements Science, JoachimPleil
of theUS Environmental ProtectionAgency, JohnYokoyama of
PerformanceAnalytical, and JerryWinberry of Envirotech
Solutions.
If you have any questions, or have input for future editions of
this guide, please feel free to contact us at Restek Corporation.
DavidM. Shelow
AirMonitoringProducts
TableofContents
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
EquipmentUsed for PassiveAir Sampling . . . . . . . . . . . . . 2
Preparing theSamplingTrain forUse . . . . . . . . . . . . . . . . . . 6
Preparing theCanister for Sampling . . . . . . . . . . . . . . . . . . . 7
FieldSampling, UsingaPassive
SamplingTrainandCanister . . . . . . . . . . . . . . . . . . . . . . . . . . 8
AnalysisofCollectedSamples . . . . . . . . . . . . . . . . . . . . . . . 10
Cleaning thePassiveSamplingTrain . . . . . . . . . . . . . . . . . 11
Cleaning theCanister . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Certifying theCanister . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-19
SilcoCan™Canisters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
TO-Can™Canisters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
MiniatureCanisters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17
TO-14&TO-15ReferenceMixes . . . . . . . . . . . . . . . . . . . 17
Air SamplingKitsandComponents . . . . . . . . . . . . 18, 19
I. Introduction
Ambient air sampling involves collecting a representative sample of ambient
air foranalysis. If theenvironment isnot changing,or if onlyaqualitative sam-
ple is needed, a simple“grab”sample canbeobtained. For example, an evacu-
ated samplecanister canbeopenedand sample rapidlycollectedat anon-con-
trolled rate, usually over several seconds, until the container attains equilibri-
um with atmospheric pressure. Generally this qualitative approach is used
when unknown analytesmust be identified, when the air contains high con-
centrationsof analytes at certain (short) times,orwhenanodor isnoticedand
a sample must be obtained quickly. Paired grab samples (before/after or
smell/no smell)oftenare employed toqualitativelydiagnoseaperceivedprob-
lem.
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.
Thereare twogeneral approaches tocollectingair samples: 1)“wholeair”sam-
plingwith canisters or Tedlar® bags and 2) “in-field concentration” sampling
using sorbent tubes or cold traps. In this guide we focus on collecting whole
air samples in canisters.Within this approach, two sampling techniques com-
monly are used: passive sampling and non-passive (active) sampling, distin-
guishedby the absence or use of an active pumpingdevice, respectively.
In passive sampling an air sample is pulled through a flow controller into an
evacuated canisterover a chosenperiodof time, ranging from5minutes to24
hours. The sampling period and the flow rate determine the canister volume
required. In active sampling, a pump is used to push the sample through a
mass flow controller and into the canister.Additional sample canbe collected,
relative to the amount that canbe collectedbypassive sampling, bypressuriz-
ing the canister with sample. Commonly the sample is pressurized to 15psig,
effectivelydoubling the samplevolume.Samplingcanbe time-integrated (e.g.,
an8-hour sample),oradip tubedesigncanbeused toestablisha flow through
the system and flush the sample containerwith sample, then, after a specified
time, the exit valve is closed and the container is pressurizedwith sample.
Although active sampling is very flexible, a drawback to using a pump is the
need for additional quality assurance requirements for sample integrity (i.e.,
no artifacts or loss of analytes).Additionally, apump requires abatteryor line
power source,whichmaypose logisticdifficulty in remote field-site sampling.
II.EquipmentUsed forPassiveAirSampling
Toensureavalid samplewhenusingapassive sampling technique, it is impor-
tant that the flow ratenot change greatlyduring the time interval specified for
the integrated sample. The proper sampling equipment helps accomplish this
objective.A typical passive sampling train should include the following com-
ponents, all constructed of stainless steel: a sampling inlet, a sintered metal
particle filter, a critical orifice, a flow controlling device, a vacuum gauge, and
a canister (Figure 1).
Sampling Inlet
The sampling inlet - the entrance to the sampling train - typically is cleaned
stainless steel tubing, either 1/4" IDor 1/8" ID.USEPACompendiumMethod
TO-14/15 recommends sampling at aheight of 2meters above the ground. In
a highly trafficked area, this would minimize the problem of dust particles
entering the sampling train. This height is not mandatory, however, and it is
common practice to use an inlet that is 12" (approximately 1/3meter) high.
The EPA also recommends having the entrance of the sampling inlet face
RestekTrademarks:
Crossbond, Rtx, SilcoCan, Siltek, Sulfinert,TO-Can, Uniliner, Plus 1,
TurningVisions IntoReality, Restek logo.
OtherTrademarks:
Freon,Tedlar,Teflon, Viton (E.I. duPont deNemours&Co., Inc.),
SUMMA (Molectrics), Veriflo (VerifloCorp., div. of Parker Hannifin
Corp.)
