United States
Environmental Protection
Agency
Environmental Monitoring
Systems Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S4-84-050 Aug. 1984
Project Summary
Passive Sampling Device for
Ambient Air and Personal
Monitoring
G.W. Wooten, J.E. Strobel, J.V. Pustinger, and C.R. McMillin
A high performance passive dosim-
eter has been developed and evaluated
as a monitor for volatile organics in
ambient air and for short-term, low-
level personal monitoring applications.
The dosimeter design was dictated by
three major areas of concern: (1)
diffusive mass transport considerations;
(2) sorbent selection, and (3) chemical
quantitation of the collected compounds,
which intimately involves desorption
procedures of the passive device.
Salient design features of the dosim-
eter included the following: (1) rugged,
simple design and cost effective; (2)
small size and simple operation; (3)
high equivalent pump rate and high
sensitivity; (4) multicomponent sampling
capability; (5) ability to be reused and
recharged; and (6) amenability to
thermal desorption.
The results of laboratory and field
evaluation studies of dosimeter perform-
ance are discussed in terms of the
design criteria employed in the develop-
ment of the device and its application to
widely divergent sampling assignments.
Detection sensitivity at the sub-ppb
level was demonstrated for short
exposure times (e.g., one hour) employ-
ing thermal desorption and halogen
specific Hall detector/gas chromatog-
raphy. Long-term exposures were
conducted under ambient air (ppb
range) and work station (ppm range)
environmental conditions. Retention
time windows and detector response
factors for 24 halogenated compounds
have been established for our computer
program to increase compound recog-
nition capabilities. The addition of a
photoionization detector extended this
capability to nonhalogen compounds of
current environmental interest.
This Project Summary was developed
by EPA's Environmental Monitoring
Systems Laboratory, Research Triangle
Park, NC to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering
information at back).
Introduction
The rapidly expanding needs of personal
and area monitoring demand passive
monitoring devices that offer the capability
of detecting multicomponent vapors at
low concentrations and are low-cost
lightweight, and convenient units. Pro-
perly designed passive dosimeters con-
taining selected polymeric adsorbents
can provide highly attractive performance
with respect to multivapor capability and
sensitivity to ppb levels.
The objective of this program was to
design, develop and evaluate a prototype
passive personal dosimeter based on
diffusion principles and employing porous
polymer sorbents that will meet all of the
performance requirements stated above.
The personal dosimeter was to be capable
of monitoring the following toxic organic
pollutants at the part-per-billion level in
ambient air: benzene, vinyl chloride, tri-
chloroethylene, tetrachloroethylene,
chloroform, carbon tetrachloride, chloro-
benzene, dichlorobenzene, 1,2-dichloro-
ethane, and trichloroethane.
The personal monitor design was to be
similar in size to a radiation badge so that
it could be easily worn. The sorbent
materials in the badge were to be chosen
so that a wide range of toxic organic
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pollutants could be monitored, or if more
selective monitoring was desired, sor-
bents could be chosen to preferentially
collect specific compounds. Laboratory
tests and evaluations of the approved
prototype were to be conducted to
determine overall performance of the unit
in the collection and analysis of the
pollutants. Testing was to include deter-
mination of sensitivity limits, selectivity,
shelf life, artifact formation, and other
salient characteristics.
Dosimeter Design
The passive dosimeter consists of a
stainless steel body, 3.8 cm diameter and
1.1 cm high, which makes the device
amenable to thermal desorption, elimi-
nates problems associated with adsorp-
tion of organics into plastic materials, and
provides a rugged, reusable device. The
internal body diameter is reduced to 3.0
cm to provide a precise containment
volume (—0.4 g) for the porous polymer.
Two sets of stainless steel screens (200
mesh wire) and perforated plates (28%
open area) are located on each side of the
polymer to confine the polymer and serve
as diffusion barriers. Friction snap rings
are used to hold the screen and plate tight-
ly against the center of dosimeter body
containing the polymer.
Application of the passive dosimeter
involves three principal areas of technol-
ogy: diffusion considerations, sorbent
selection, and chemical quantitation of
the sampled compounds.
The diffusion rate of organic compounds
onto the adsorbent is based on the types of
compounds of interest and their diffusion
constants, the ambient concentration of
the compounds, and the diffusion path
the compounds must take to get to the
adsorbent. Diffusion rates for several
chlorinated organic compounds were
calculated as well as defined by laboratory
tests as part of this contract as discussed
later in this report.
Selection of adsorbent materials is
based on the ability of the sorbent to hold
the compounds of interest at the sampling
conditions and then readily release the
compounds at the desorption conditions
with minimum background interference.
Chemical quantification of exposed
passive dosimeters entails a two-step
procedure. The first step involves the
removal (desorption) of collected com-
pound(s) and the second involves the
determination of compounds. Typically,
the procedures used are thermal desorp-
tion and a gas chromatographic (GC)
procedure with a specific detector (for
example, electron capture or photoioniza-
tion detector) for the compounds of
interest.
Test Equipment
Gas standards were generated for
dosimeter evaluation studies using a
sample generation system employing a
syringe drive of fluids into heated blocks
with three calibrated dilution stages.
Dosimeters were exposed to gas
standards in one of two exposure
chambers. The first chamber was a 2-liter
borosilicate glass jar fitted with an "0"-
ring-sealed Teflon lid and multiple
Swagelok® fittings for gas injection,
sampling, and gas outlet. Dosimeters
hung in the center of the jar, sampling the
contaminated air during grab type tests.
The second chamber was a thick-
walled, flanged, borosilicate glass pipe by
which dosimeters could be subjected to a
range of concentrations, temperatures,
humidities, and flow velocities. Sorbent
tubes were used to collect known
volumes of sample to validate gas
constituent concentrations with either
chamber during the tests.
Results
Sorbent Selection
Porapak R and Tenax GC were evalu-
ated as sorbent materials for use in the
dosimeters, based on their high break-
through volumes and clean background
on the thermal desorption. The Porapak R
sorbent provided good results at most
concentration levels, however, at low
concentration levels (~1 ppb), recovery of
spiked samples for several chlorinated
compounds was low (40% to 50%).
Exposure studies using Tenax GC were
more encouraging with recovery efficien-
cies for all components greater than 93%.
Tenax GC was subsequently chosen as
the adsorbent material for all future
dosimeter tests.
Performance Testing
Initial tests performed on the dosimeter
defined the response of the analytical
systems with compound mass collected
on the dosimeter, the sample concentra-
tion range, equivalent sampling rates,
effects of concentration and exposure
time on dosimeter sampling rates, and
storage of samples.
A linear response was verified for the
quantity of organic compound on sorbent
and the GC response. This response was
verified for chloroform, carbon tetrachlo-
ride, 1,1,2-trichloroethane, chloroben-
zene, 1,2-dichloroethane, trichloroethy-
lene, and tetrachloroethylene.
Dosimeter calibration curves were
developed for the low concentration
range (1-50 ppbv) and extended up to
approximately 10 ppmv (see Figure 1).
These curves were established by expo-
sing dosimeters in the sample exposure
chambers for varying times and concen-
trations.
350,.
0 10 20 30 40 SO
Concentration x Time, ppbv-hr
Figure 1. Example response curve (1,2-
dichloroethane).
Sampling rates for dosimeters were
defined by comparing the dosimeter with
active sorbent sampling tubes. Simulta-
neous samples were collected by exposing
dosimeters within the chamber and by
withdrawing gas samples from sample
ports into the sorbent tubes. Sampling
times were varied between one and four
hours. Two-sided dosimeter exposure
resulted in equivalent sampling rates of
50 to 60 cc/min. Averaged equivalent
sampling rates for one-sided exposure
ranged 25 to 34 cc/min as shown in
Table 1.
To determine the effect of concentra-
tion and time on dosimeter performance,
triplicate exposures were made at 1 -, 2-,
4-, 8-, and 16-hour durations and at con-
centrations of 1, 10, and 100 ppbv. Typi-
cally, there is a decrease in sampling rate
for the more volatile compounds (i.e.,
chloroform, 1,2-dichloroethane, and
carbon tetrachloride) at the ppb level as
exposure time is increased above ap-
proximately 4 hours.
Studies to determine the extent in
which compounds were lost during
storage was also evaluated. Exposed•
dosimeters were capped with friction-
tight Teflon caps, sealed in screw-cap
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Table 1 . A verage Equivalent Samp/ing Hates (Single- faced Sampling}
1.2- Carbon
Chloro- Dichloro- tetra- Trichloro-
form ethane chloride ethylene
Pump rate.
cc/min 25.0 26.8 21.8
Std. dev. ±5.0 ±2.9 ±5.2
glass jars, and maintained under ambient
laboratory conditions for twelve days.
Only 10 to 18% decrease was observed
from the 30 ng spike after the 12 days,
except for carbon tetrachloride which
showed a 50% decrease.
Sampling Tests
Laboratory validations tests were
conducted by varying sampling times and
concentrations for single- and dual-faced
exposures. Multiple dosimeters and
tubes were typically used for each test.
Typical results for the validation tests,
shown in Tables 2 and 3, indicate that the
dosimeters have the ability to identify
compounds and concentrations similar to
the tube results or the expected gas
standard concentrations.
Small-scale field studies were performed
to provide additional dosimeter validation
information. The first study conducted
found good recoveries of the laboratory
spikes. In addition, clean dosimeter
blanks were found. Variation in tempera-
tures (80°F to 90°F), relative humidities
(50% to 80%), and wind velocity (5 mph to
25 mph) appeared not to effect results.
Work station monitoring conducted in a
second field study showed good compari-
sons between dosimeter and charcoal
and solid sorbent tubes. As shown in
Table 4, good agreement was shown for
1 ,2-dichloroethane between the dosimeter
and charcoal tubes with one exception
(attributed to the fact that the dosimeter
may have been shielded by protective
clothing). Table 5 shows additional
results from this study comparing sorbent
tube and dosimeter. In addition, one 5-
hour sample compared well with the
sum of five consecutive 1-hour samples.
Conclusions and
28.3
±1.5
1, 1,2- Tetra-
Trichloro- chloro- Chloro-
ethane ethylene benzene
27.7 29.5
±0.6 ±1.9
Table 2. Single-Face Sampling for One Hour
Concentration Concentration.
PP°V P*rrant PPbv *
Compound
Chloroform
1 ,2-Dichloroethane
Carbon tetrachloride
Trichloroethylene
1, 1 ,2-Trichloroethane
Tetrachloroethylene
Chlorobenzene
Table3. Dual-Face
Compound
Chloroform
1 ,2-Dichloroethane
Carbon tetrachloride
Trichloroethylene
1. 1 ,2-Trichloroethane
Tetrachloroethylene
Chlorobenzene
Theory
11.6
13.7
8.8
1O.4
1O.2
8.2
12.1
Tube
11.1
13.7
10.6
10.2
11.1
8.6
11.0
recovery Dos/meter
96 12.9
100 13.8
120 9.7
98 12. 1
109 12.5
105 13.7
91 12.4
Sampling Integration Experiment B (1 ppbv - 45 min; lOOppbv
Concentration, Concentration,
PP°V P»r^nt PPto ^
Theory
28.0
33.8
21.7
25.4
25.0
20.1
29.7
Tube
26.5
33.6
22.6
24.3
26.7
19.8
32.0
Table 4. 1 ,2-Dichloroethane Sampling with
Parameter
Flow rate, mL/min
Amount collected, tig
Exposure time, hr
Concentration,
W/L.
ppmv
Equivalent. mL/min
pump rate
Amount collected, fig
Exposure time, hr
Concentration.
ug/L
ppmv
1
47.2
81
5.6
5.1
1.3
90
30.0
64.0
5.6
6.3
1.6
recovery Dosimeter
95 26.7
99 28. 1
104 24.0
96 27.7
107 29.8
99 28.8
108 33.9
Charcoal Tubes and Passive Monitors
Charcoal Tube No.
2 3
46.2 50.2
456 305
5.6 5.6
27.8 18.2
6.9 4.5
Dosimeter No.
91 92
30.0 30.0
277 212
5.6 5.6
25.9 21.0
6.4 5.2
34.3
±4.0
Ratio
isimeter/
tube
1.17
1.OO
0.91
1.19
1.13
1.59
1.13
- 15 min)
Ratio
Dimeter/
tube
1.01
0.84
1.06
1.14
1.12
1.43
1.06
4
49.0
17,865
5.6
1.O27
254
93
30.0
1,536
5.6
144.0
35.6
Recommendations
A high performance passive dosimeter
was developed to meet the rapidly
expanding needs of ambient air and
short-term, low-level, personal monitor-
ing. This device, employing a porous
polymer as the sorbent medium, satisfies
the stringent requirements imposed by
ambient air sampling. Detection sensitiv-
ities in the part-per-trillion (ppt) to part-
per-billion (ppb) range have been demon-
strated for seven halogenated organic
compounds at exposure times of about one
hour. Retention time and detector response
data for twenty-four halogenated com-
pounds were developed to extend com-
pound recognition capabilities. This
simple, inexpensive monitor demonstrates
multicomponent sampling capabilities.
Sampling performance of the passive
device is comparable to active "pumped"
sampling tubes. Device performance is
provided by the equivalent pump rate
characteristics, the high sample recovery
via a thermal desorption process, and the
detection sensitivity and specificity
afforded by multiple specific detector GC
analysis.
While in-depth laboratory and field
evaluation studies have been conducted
with the monitor, more comprehensive
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field studies should be completed to
demonstrate the practical applicability of
the monitor to real sampling problems.
Hazardous waste sites represent a timely
sampling problem that would provide a
good practical evaluation of the monitor.
TableS. Work Station Sampling Studies
Mass collected, ng
Dosimeter sample interval
Compound 1 hr 2 hr 3 hr 4 hr 5 hr
Dosimeter
5-hr
Z exposure
Passive dosimeter
J ,2-Dichloroethane
Trichloroethylene
1,1,2-Trichloroethane
Tetrachloroethylene
Chlorobenzene
Pumped tube
0.27
0.58
0.16
0.25
8.4
0.29
0.38
0.48
0.38
18.2
0.24
0.25
.
.
10.4
0.20
0.11
0.38
0.15
8.6
-0.10
0.16
0.48
0.12
6.7
-1.1
1.48
1.50
0.90
51.0
0.67
1.47
0.90
0.66
51.0
1 ,2-Dichloroethane
Trichloroethylene
1, 1 ,2-Trichloroethane
Tetrachloroethvlene
Chlorobenzene
0.34
0.43
0.49
0.11
7.5
0.14
0.22
9.6
0.13
0.15
0.59
0.17
5.4
G. W. Wooten, J. E. Strobel. J. V. Pustinger, andC. R. McMillin are with Monsanto
Company, Dayton, OH 45407.
James D. Mulik is the EPA Project Officer (see below).
The complete report, entitled "Passive Sampling Device for Ambient Air and
Personal Monitoring," (Order No. PB 84-210 046; Cost: $10,00, subject to
change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Environmental Monitoring Systems Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
•tf U S GOVERNMENT PRINTING OFFICE. 1984 — 759-015/7768
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
LO.J
IL
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