United States
Environmental Protection
Agency
Environmental Monitoring Systems
Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S4-82-064 Jan. 1983
Project Summary
Stability of Organic Audit
Materials and Results of
Source Test Analysis Audits
R. K. M. Jayanty, W. F. Gutknecht, C. E. Decker, J. E. Knoll, and D. J.
von Lehmden
A repository of 40 gaseous
compounds including hydrocarbon,
halocarbon, and sulfur species has
been established under contract with
the U.S. Environmental Protection
Agency (USEPA). The main objectives
of this on-going project are (1) to
provide gas mixtures to EPA, state/
local agencies, or their contractors, as
performance audits to assess the
accuracy of source emission
measurements in certain organic
chemical manufacturing industries,
(2) to corroborate the vendor's
certified analysis of the gas mixtures
by in-house analysis, (3) to determine
the stability of the gas mixtures with
time by in-house analysis, and (4) to
explore the feasibility of new audit
materials as requested by EPA.
Thus far, 18 compounds have been
used to conduct 86 different audits.
The results of these audits and a
description of the experimental
procedures used for analyses and
available stability data are presented
in the status report. Seventy percent
of the audit results are within 10
percent of the expected values.
Compound stabilities have been
determine through multiple analyses
of the cylinders containing them.
Stability values for all compounds are
expressed as percent change per
month. Calculated changes are
typically found to be a few tenths of
one percent per month, though many
of these changes may not be signifi-
cantly different from zero.
This Project Summary was devel-
oped by EPA's Environmental
Monitoring Systems Laboratory,
Research Triangle Park, NC, to
announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
Accurate measurement of hydro-
carbons, halocarbons, and sulfur-
containing compounds in ambient and
source samples is essential to any
environmental monitoring program.
The potential for achieving acceptable
accuracy is enhanced by the availability
of reliable standards which can be used
to check or validate the measurement
process. The Research Triangle
Institute (RTI) under contract to the
Environmental Monitoring Systems
Laboratory, U.S. Environmental
Protection Agency (USEPA), has
responded to this need by developing an
extensive repository of standard
i gaseous compounds. These standards
are to be used in performance audits as
designated by the EPA Project Officer.
These performance audits are to assess
the accuracy of source emission
measurements in certain organic
manufacturing industries.
The RTI repository currently contains
40 different compounds based on
anticipated needs of EPA. Table 1 lists
the compounds, the . concentration
ranges of each compound, and the
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Table 1. Audit Materials Currently Held in the Repository
Low Concentration Range High Concentration Range
Compound
No. of
Cylinders
Concentration
Range (ppm)
No. of
Cylinders
Concentration
Range (ppm)
Benzene 14
Ethylene 4
Propylene 4
Methane/Ethane
Propane 4
Toluene 2
Hydrogen Sulfide 4
Meta-Xylene 2
Methyl Acetate 2
Chloroform 2
Carbonyl Sulfide 2
Methyl Mercaptan 4
Hexane 2
1,2-Dichloroethane 4
Cyclohexane
Methyl Ethyl Ketone 1
Methanol 1
1.2-Dichloropropane 2
Trichloroethylene 2
1,1 -Dichloroethylene 2
1,2-Dibromoethylene 2
Perchloroethylene 2
Vinyl Chloride 9
1,3-Butadiene 1
Acrylonitrile 2
Aniline 1
Methyl Isobutyl Ketone 1
Cyclohexanone 2
Para-dichlorobenzene 2
Ethylamine 2
Formaldehyde
Methylene Chloride 1
Carbon Tetrachloride 1
Freon 113 1
Methyl Chloroform 1
Ethylene Oxide 1
Propylene Oxide 1
Allyl Chloride 1
Acrolein 1
Chlorobenzene 1
Carbondisulfide 1
8- 13
5-20
5-20
17
4
6
4
4
60
300
3000
300
WOO
200
300
300
300
300
300
300
100
-400
- 700
- 20.000
- 700
- 6000(MJ,
- 700(E)
- 700
-700
-700
-700
•700
-700
-300
number of cylinders of each compound.
Additional compounds are obtained as
needed.
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 standard gas during
performance audits. The compressed
gas cylinder is especially suitable as an
audit material because of its simplicity,
portability, low cost, flexibility in analyte
delivery over a broad concentration
5-20 4
5-20 2
5-20 2
5-20 2
5-20 2
5-20 2
5-20 2
3-10 -
20-80 2 1000 • 3000
5-20 4 100-600
/ 700
50 -
50 -
5-20 2 300 - 700
5-20 2 100-600
5-20 2 100-600
5-20 2 100- 600
5-20 2 300 - 700
5-30 -
25 -
5-20 2 300-700
10 -
10 1 50 - 100
5-20 .
10-40 -
10 - 60 -
10 -
10 -
10 -
10 -
10 -
5-20 1 75 - 200
5-20 / 75-200
5-20 1 75-200
5-20 -
5-20 1 75-200
range, reliability, and ruggedness for
interstate shipping. The accuracy of the
supplier-reported levels of these
compounds are verified through
measurement using National Bureau of
Standards - Standard Reference
Materials (NBS-SRM's), commercial
permeation tubes, and/or reagent
grade pure liquids as standards. The
permeation rate of the commercially
available tubes are verified 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 performed. This study involves
periodic analyses of the contents of
each of the cylinders in the repository.
Procedure
Once a compound is chosen, a
commercial supplier is contacted to
determine if a cylinder containing that
compound can be prepared. If so, the
manufacturer prepares the cylinder
gases and determines the concentra-
tion of the analyte in the cylinder. The
cylinder is sent to RTI where its contents
are analyzed within seven days of its
arrival. If the RTI value varies from the
manufacturer's value by more than 10
percent, an analysis is performed by a
third party. The cylinder contents are
then analyzed one month after
acquisition, two months after
acquisition, and one year after acqui-
sition. The cylinder contents are also
analyzed before a cylinder is sent out for
an audit. This preaudit analysis may
substitute for the annual analysis if it
occurs within a month of the normal
analysis due date.
All analyses are carried out using gas
chromatography. The column and
detector are chosen so as to be optimum
for the compound being measured.
Three types of standards are used to
generate gas concentrations for
calibration of the GC for the measure-
ment of audit materials. National
Bureau of Standards - Standard
Reference Materials (NBS-SRM)
methane and propane are used as
standards for the measurement of
methane and propane audit materials.
These same gases are used to calibrate
the chromatographic system for
measurement of ethylene and
propylene, assuming the FID response
per carbon is constant for compound to
compound. In a few others (e.g., vinyl
chloride, ethylene oxide) gaseous
standards are generated using
permeation tubes. The standards for
most of the other audit materials are
prepared using pure liquids which are
volatized in a clean glass bulb.
Audit requests are directed to RTI
through the EPA Project Officer. The
cylinder and a regulator are then
shipped by a freight carrier to the
laboratory being audited. A letter is also
included with the cylinders which
provides general instructions for
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performance of the audit. The audit
concentrations are provided to the
requesting agency audit coordinator.
After the laboratory being audited has
analyzed the contents of the cylinder,
the audit coordinator reports the
value(s) to RTI, which in turn reports
both the measured and accepted values
to the Project Officer. The laboratory
being audited then is responsible for
shipping the cylinder and regulator back
to RTI.
Results and Discussion
To date, 86 individual audits have
been initiated, and 83 are complete. The
results obtained for a few typical
performance audits are shown in Table
2 and the rest are given in the full report.
Generally, the results of the audits
show close agreement (±.10%) with the
actual cylinder concentrations
measured prior to shipment.
Most of the cylinders in the repository
are analyzed at least four times to
determine the stability of these
compounds; some are analyzed as many
as eight times. An estimate of stability
has been made for each cylinder that
Table 2. Typical Audit Results
has been analyzed at least three times.
This estimate is a calculation of percent
change in concentration per month over
the period that RTI has performed
analyses of the cylinder contents. The
calculation involves a linear regression
analysis of the concentration of the
analyte versus time in days. The slope
and intercept determined by this
regression analysis are then used to
calculate percent change per month by
the relationship:
slope
% Change/Month =
y intercept
100x30
Examples of stability data are shown in
Table 3. Changes are noted for each
compound, although these changes
may not be significantly different from
zero. As the number of analyses per
cylinder increases, additional statistical
analyses will be performed.
Conclusions
Cylinder gases of hydrocarbons,
halocarbons, and sulfur species have
been used successfully to assess the
Industry
Audit Material
Cylinder
Concentration Client Audit
(ppm) Accuracy
Maleic anhydride
production
Ester production
Vegetable oil plant
Coke oven by-product
Benzene in N
Propane in Air
Hexane in N
Benzene in N
138
300
10.1
710
82.2
1982
88.4
8.2
-9.4
+4.7
+8.6
+8.6
+5.6
+3.0
-8.7
+2.6
accuracy of gas chromatographic
systems used to measure organic
compounds in source emissions.
Absolute accuracy has not been
determined because of lack of standard
reference materials; instead, interlabor-
atory bias has been reported for the
performance audits conducted during
source testing. The interlaboratory bias
determined has been generally within
10 percent for both low and high
concentration gases.
Twenty-six out of 40 gaseous
compounds have demonstrated
sufficient stability in cylinders for use as
audit materials. Four compounds
(ethylamine, paradichlorobenzene,
cyclohexanone, and aniline) are not
recommended as audit materials for
various reasons as discussed in the full
report. Another 10 compounds (carbon
tetrachloride, methylene chloride,
methyl chloroform, Freon 113, ethylene
oxide, propylene oxide, alkyl chloride,
acrolein, ch lorobenzene and
carbondisulfide) have recently been
added to the repository; the stability of
these compounds remains to be
studied. The estimates of stability are
reported in terms of percent change per
month. Detailed statistical analyses
which would separate statistical
deviations from true concentration
change with time are in progress and
will be presented in a journal
publication.
Table 3. Typical Stability Results
Compound
Concentration Period of Cylinder
(ppm) Analyses (months) % Change/Month
Benzene
Benzene
Hydrogen sulfide
1,2 Dichloroethane
Perchloroethylene
Acrylonitrile
Chloroform
Propylene
12.2
296
9.15
439
13.0
20.1
348
14.8
25
27
37
28
13
28
33
25
-0.15
0.01
-0.05
-0.10
-0.23
-1.07
-0.20
0.06
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R. K. M. Jayanty, W. F. Gutknecht, and C. E. Decker are with Research Triangle
Institute, Research Triangle Park, NC 27709; the EPA authors J. E. Knoll and
D. J. von Lehmden (also the EPA Project Officer, see below) are with the
Environmental Monitoring Systems Laboratory, Research Triangle Park, NC
27711.
The complete report, entitled "Stability of Organic Audit Materials and Results
of Source Test Analysis Audits," (Order No. PB 83-107 490; 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
•(t U.S. GOVERNMENT PRINTING OFFICE: 1983 6S9-O17/O881:
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Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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Fees Paid
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Penalty for Private Use $300
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