2
dependable
execution
One of our standing goals is to provide you with practical
information to help you obtain reliable data from your
chromatographic and peripheral systems. This guide describes
equipment needed and practical techniques to follow when
collecting passive air samples, using canisters. It is a
compilation of information based on our experience and that of
experts in this field. We would like to thank the individuals who
provided invaluable assistance in the development of this guide:
Dr. Eric Winegar of Applied Measurements Science, Joachim Pleil
of the US Environmental Protection Agency, John Yokoyama of
Performance Analytical, and Jerry Winberry 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.
David M. Shelow
Air Monitoring Products
Table of Contents
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Equipment Used for Passive Air Sampling . . . . . . . . . . . . . . 2
Preparing the Sampling Train for Use . . . . . . . . . . . . . . . . . . . 6
Preparing the Canister for Sampling . . . . . . . . . . . . . . . . . . . . 7
Field Sampling, Using a Passive
Sampling Train and Canister . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Analysis of Collected Samples . . . . . . . . . . . . . . . . . . . . . . . . . 10
Cleaning the Passive Sampling Train . . . . . . . . . . . . . . . . . . 11
Cleaning the Canister . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Certifying the Canister . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-19
SilcoCan™ Canisters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
TO-Can™ Canisters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Miniature Canisters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17
TO-14 & TO-15 Reference Mixes . . . . . . . . . . . . . . . . . . . . 17
Air Sampling Kits and Components . . . . . . . . . . . . . 18, 19
I. Introduction
Ambient air sampling involves collecting a representative sample of ambient
air for analysis. If the environment is not changing, or if only a qualitative sam-
ple is needed, a simple “grab” sample can be obtained. For example, an evacu-
ated sample canister can be opened and sample rapidly collected at a non-con-
trolled rate, usually over several seconds, until the container attains equilibri-
um with atmospheric pressure. Generally this qualitative approach is used
when unknown analytes must be identified, when the air contains high con-
centrations of analytes at certain (short) times, or when an odor is noticed and
a sample must be obtained quickly. Paired grab samples (before/after or
smell/no smell) often are employed to qualitatively diagnose a perceived prob-
lem.
To obtain a more representative sample requires time-integrated sampling. A
flow restrictor is used to spread the sample collection flow over 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 the environment and is preferred when, for regulatory or health
reasons, a typical exposure concentration is required for a situation that may
have high variability, as in an occupational setting.
There are two general approaches to collecting air samples: 1) “whole air” sam-
pling with 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-
guished by the absence or use of an active pumping device, respectively.
In passive sampling an air sample is pulled through a flow controller into an
evacuated canister over a chosen period of time, ranging from 5 minutes to 24
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 can be collected,
relative to the amount that can be collected by passive sampling, by pressuriz-
ing the canister with sample. Commonly the sample is pressurized to 15psig,
effectively doubling the sample volume. Sampling can be time-integrated (e.g.,
an 8-hour sample), or a dip tube design can be used to establish a flow through
the system and flush the sample container with sample, then, after a specified
time, the exit valve is closed and the container is pressurized with 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, a pump requires a battery or line
power source, which may pose logistic difficulty in remote field-site sampling.
II. Equipment Used for Passive Air Sampling
To ensure a valid sample when using a passive 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 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" ID or 1/8" ID. US EPA Compendium Method
TO-14/15 recommends sampling at a height of 2 meters 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 1/3 meter) high.
The EPA also recommends having the entrance of the sampling inlet face
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Crossbond, Rtx, SilcoCan, Siltek, Sulfinert, TO-Can, Uniliner, Plus 1,
Turning Visions Into Reality, Restek logo.
Other Trademarks:
Freon, Tedlar, Teflon, Viton (E.I. du Pont de Nemours & Co., Inc.),
SUMMA (Molectrics), Veriflo (Veriflo Corp., div. of Parker Hannifin
Corp.)