United States
Environmental Protection
Agency
Environmental Monitoring Systems
Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S4-85/032 June 1985
&EPA Project Summary
Stability of Parts-Per-Billion
Hazardous Organic Cylinder
Gases and Performance Audit
Results of Source Test and
Ambient Air Measurement
Systems: Status Report #1
R. K. M. Jayanty, S. W. Cooper, J. Sokash, C. E. Decker, and D. J. von Lehmden
A repository of 14 gaseous organic
compounds at parts-per-billion (ppb)
levels in compressed gas cylinders has
been established under the contract
with the Environmental Protection Agen-
cy (EPA), the primary objectives of this
on-going project are: (1) to provide
accurate gas mixtures to EPA, state/
local agencies, or their contractors for
performance audits to assess the rel-
ative accuracy of source measurement
systems during hazardous waste trial
burn tests and ambient air monitoring
programs; (2) to verify the manufactur-
er's certified analysis of the multi-com-
ponent gas mixtures with time; (3) to
determine the stability of the gas mix-'
tures with time; and (4) to develop new
audit materials as requested by EPA.
The repository consists of two mix-
tures of five and nine organic compounds
each. These mixtures were blended in
aluminum cylinders in a balance gas of
nitrogen. The five component mixture
(Group I) contains carbon tetrachloride,
chloroform, perchloroethylene, vinyl
chloride, and benzene. The nine com-
ponent mixture (Group II) includes
trichloroethylene, 1,2-dichloroethane,
1,2-dibromethane, acetonitrile, trichlo-
rofluoromethane, dichlorodifluorome-
thane, bromomethane, methyl ethyl
ketone, and 1,1,1-trichloroethane. To
date, 20 performance audits have been
initiated and 12 are complete. The results
of these audits and a description of the
experimental procedures used for anal-
yses and available stability data are
presented in this status report. General-
ly, the results of the audits show close
agreement (plus or minus 50 percent)
with the audit material concentrations
measured by Research Triangle Institute.
Limited stability studies of all 14
gaseous organic compounds have been
performed. Results indicate that all the
compounds tested are adequately stable
for use as reliable audit materials.
Detailed statistical analyses which
would separate statistical deviations
from true concentration changes with
time are in progress and will be pre-
sented in a future report.
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 infor-
mation at back).
Introduction
The application of Quality assurance
practices is important to the generation of
high-quality environmental data. The
Quality Assurance Division of EPA's
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Environmental Monitoring Systems Lab-
oratory has initiated a program to supply
audit materials for use during hazardous
waste trial burn tests and ambient air
measurements. The Research Triangle
Institute (RTI), under contract to the U.S.
Environmental Protection Agency
(USEPA), has responded to this need
through development of a repository of 14
gaseous organic compounds at parts-per-
billion (ppb) levels in compressed gas
cylinders. The gaseous compounds are to
be used in performance audits as desig-
nated by the EPA Project Officer. These
performance audits are to assess the
relative accuracy of source measurement
systems during hazardous waste trial
burn tests and ambient air monitoring
programs.
The repository currently contains 14
compounds selected on the basis of
anticipated needs of EPA's Office of Solid
Waste. Table 1 lists the 14 compounds,
the concentration ranges, andthe number
of cylinders for each group in the repos-
itory. The balance gas for all gas mixtures
is nitrogen and the cylinder construction
material is aluminum.
The gaseous compounds are acquired
from commercial suppliers in compressed
gas cylinders; these same cylinders, along
with an appropriate delivery system, are
used directly as sources of the gaseous
compounds during performance audits.
The accuracy of the supplier-reported
levels of these compounds are verified
through measurement using commercial
permeation tubes. The permeation rates
of the commercially available tubes are
verified gravimetrically by RTI before use.
The accuracy of the "known" cylinder
concentrations and the stability of the
compounds in the cylinders are important.
Along with acquisition of new compounds
and verification of their concentrations,
an extensive stability study is being
performed. This study involves periodic
analyses of the contents of each of the
cylinders in the repository.
Procedure
Once a mixture of compounds is chos-
en, a commercial supplier is contacted to
determine if a cylinder containing those
compounds can be prepared. If so, the
manufacturer prepares the cylinder gases
and determines the concentration of the
analytes in the cylinder by at least two
times. The cylinder is sent to RTI where its
contents are analyzed usually within ten
days of its arrival. If the RTI value varies
from the manufacturer's value by more
than 25 percent, an analysis is usually
Table 1. PPB Level Organic Gases in
Repository
Group
Group 1*
Group II"*
No. of
Cylinders
20
12
13
3
Concentration
Range of
Each Compound
(ppb)
7-90
90-430
7-90
90-430
"Group I Compounds—carbon tetrachloride,
chloroform, perchloroethylene, vinyl chlo-
ride, and benzene.
""Group II Compounds—trichloroethylene,
1,2, -dichloroethane, 1,2-dibromoethane,
acetonitrile, trichlorofluoromethane (Freon-
111, dichlorodifluoromethane (Freon-12),
bromoethane, methylethylketone, and
1,1,1 -trichloroethane.
performed by a third party (EPA or NBS).
The gas mixtures are again analyzed at 2
months, 6 months, and at one year
following the initial analysis to determine
the stability of the gas mixtures.
All analyses are performend using a
Hewlett-Packard 5880A gas chromato-
graph equipped with flame ionization and
electron capture detectors. The electron
capture detector (ECD) has been used
principally for measurement of all the
chlorinated hydrocarbons except vinyl
chloride. Vinyl chloride, benzene, methyl
ethyl ketone, and acetonitrile are analyzed
with flame ionization detector (FID). The
gaseous samples are injected onto the
columns by means of a six-port gas
sampling valve constructed of Hastalloy C
(high nickel content and low adsorption
properties) mounted near the injection
port. The valve is equipped with inter-
changeable sampling loops (1 cc and 10
cc) to allow the injection of variable but
known volumes of gas. The gas chromato-
graphic parameters used in the measure-
ment of individual compounds are des-
cribed in the status report.
Permeation tubes purchased from Met-
ronics are generally used as calibration
standards for all 14 organic compounds
unless otherwise specified. The permea-
tion rate of each permeation tube is
determined every 15 to 30 days by
weight-loss determination of each tube.
The RTI supplies repository cylinders
for audits upon request from the EPA,
state, or local agencies or their contrac-
tors. When a request is received, the
cylinder is then shipped by a freight
carrier to the laboratory being audited. A
letter is also included with the cylinder
which provides general instructions for
performance of the audit. The audi
concentrations are provided to the re
questing agency Audit Coordinator. Aftei
the laboratory being audited has analyzec
the contents of the cylinder, the Audi'
Coordinator reports the value(s) to RTI
which in turn reports both the measurec
and accepted values to the Project Officer
There is no charge for the audit except the
cost of returning the audit cylinder.
Results and Discussion
To date, 20 performance audits have
been initiated; 15 are complete. All audits
initiated have been for Group I com-
pounds, since Group II compounds have
only recently been verified and approved
for performance audits. The results ob-
tained for a few typical performance
audits are shown in Table 1 and the rest
are given in the status report. Generally,
the audit results are within ± 50 percent
of the audit concentrations measured by
RTI.
Most of the cylinders in the repository
are analyzed two to three times to deter-
mine the stability of the compounds.
Relative accuracies of the cylinder gas
analyses for Group I compounds have
been determined using the NBS primary
standards. However, relative accuracies
of cylinder gas analyses for Group II
compounds will not be established until
NBS primary standards are analyzed in
conjunction with these gas cylinders. This
will be done during the third RTI analyses
of group II cylinder gases. An examination
of stability data in the status report shows
values for Group I individual cylinder gas
analyses usually vary by less than 10
percent for 3 analyses over an 8-month
period. Since only 3 months of stability
analyses are currently available in Group
II cylinders, a statement of the variability
will be made in a future report. This
variation indicates changes in cylinder
contents (i.e., instability) and the impreci-
sion of the measurement process. The
possible sources of experimental error
that could result in apparent changes in
concentrations include: (1) the variability
of the analytical technique used for
analyses; (2) stability of and/or accuracy
of calibration standards; and (3) the
accuracy of reproducing standards. Each
of these sources of variability contributes
to the net uncertainty of the resulting
stability data. Estimates of day-to-day
measurement uncertainty (repeatability)
for Group I and Group II compounds have
not been performed at the present time.
However, the repeatability measure-^
ments to determine the total uncertainty^
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will be performed in the near future. The
repeatability measurement results will be
included in a future report. The uncertain-
ty for the gas chromatographic measure-
ment has been determinedto be less than
3 percent by multiple injections of the gas
during same-day analysis.
Conclusions
A repository of 14 gaseous organic
compounds at parts-per-billion levels in
compressed gas cylinders has been used
successfully in audits to assess the
relative accuracy and precision of anal-
ytical systems, especially those used
during hazardous waste trial burn tests
and ambient air monitoring. To date, 20
performance audits have been initiated
and 15 are complete. Generally the audit
results are within ± 50 percent of the
audit concentrations measured by RTI.
Limited stability studies of all 14 gas-
eous organic compounds have been
performed to determine the feasibility of
using them as audit materials. Results
indicate that all of the organics tested are
adequately stable to be used as reliable
audit materials. Detailed statistical anal-
yses which would separate statistical
deviations from true concentration chang-
es with time are in progress and will be
presented in a future report.
R. K. M. Jayanty, S. W. Cooper. J. Sokash. and C. £. Decker are with Research
Triangle Institute, Research Triangle Park. NC 27709.
DarrylJ. von Lehmden is the EPA Project Officer (see below}.
The complete report, entitled "Stability of Parts-Per-Bil/ion Hazardous Organic
Cylinder Gases and Performance Audit Results of Source Test and Ambient Air
Measurment Systems. "(Order No. PB85-188 860/AS; Cost: $11.50. 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
* U.S. GOVERNMENT PRINTING OFFICE: 1965-559-01027080
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