yyEPA
United States
Environmental Protection
Agency
Environmental Monitoring and
Support Laboratory
Cincinnati OH 45268
EPA-600/4-80-025
April 1980
Research and Development
Performance
Tests for the
Evaluation of
Computerized Gas
Chromatography/
Mass Spectrometry
Equipment and
Laboratories
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been groyped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Eliminatipn of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are: . I
1, Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research i
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9, Miscellaneous Reports
This report has been assigned tolthe ENVIRONMENTAL MONITORING series.
This series describes research conducted to develop new or improved methods
and instrumentation for the identification and quantification of environmental
pollutants at the lowest conceivably significant concentrations. It also includes
studies to determine the ambient concentrations of pollutants in the environment
and/or the variance of pollutants ajs a function of time or meteorological factors.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 122161.
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EPA-600/4-80-025
April 1980
PERFORMANCE TESTS FOR THE EVALUATION
OF COMPUTERIZED
GAS CHROMATOGRAPHY/MASS SPECTROMETRY
EQUIPMENT AND LABORATORIES
by
William L. Budde
and
James W. Eichelberger
. Physical and Chemical Methods Branch
Environmental Monitoring and Support Laboratory
Cincinnati, Ohio 45268
ENVIRONMENTAL MONITORING AND SUPPORT LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
-------
DISCLAIMER
This report has been reviewed by the Environmental Monitoring and
Support Laboratory, U.S. Environmental Protection Agency, and approved for
publication. Mention of trade names or commercial products does not
constitute endorsement or recommendation for use.
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FOREWORD
Environmental measurements are required to determine the quality of
ambient waters and the character of waste effluents. The Environmental
Monitoring and Support Laboratory - Cincinnati, conducts research to:
• Develop and evaluate methods to measure the presence and concentra-
tion of physical, chemical, and radiological pollutants in water,'
wastewater, bottom sediments, and solid waste.
• Investigate methods for the concentration, recovery, and identifica-
tion of viruses, bacteria and other microbiological organisms in
water; and, to determine the responses of aquatic organisms to water
quality.
• Develop and operate an Agency-wide quality assurance program to assure
standardization and quality control of systems for monitoring water
and wastewater.
• Develop and operate a computerized system for instrument automation
leading to improved data collection, analysis, and quality control.
This report was developed by the Advanced Instrumentation Section of the
Environmental Monitoring and Support Laboratory. It describes a series of
general purpose tests to evaluate the performance of computerized gas
chromatography-mass spectrometry (GC/MS) systems. Some of the tests go
beyond equipment performance and may be used to evaluate the performance of
laboratories using GC/MS for organics analysis. The report will be useful
to the many Federal, State, local government, and private laboratories that
are planning to employ this powerful analytical tool.
Dwight G. Ballinger
Director
Environmental Monitoring and Support
Laboratory - Cincinnati
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ABSTRACT
A series of ten general purpose tests are described which are used to
evaluate the performance of computerized gas chromatography-mass
spectrometry systems. All of the tests use the continuous, repetitive
measurement of spectra method of data acquisition, and no selected ion
monitoring tests are included. Evaluation criteria are given with each
performance test. Some of the tests go beyond equipment performance, and
may be used to evaluate the performance of laboratories using GS/MS for
organics analysis.
iv
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CONTENTS
Foreword .. .iii
Abstract iv
Figures V1
Tables vi
Acknowl edgment ' , v i i
1. Introducti on 1
2. Summary of Tests 3
3. Experimental Procedures 5
Test I Spectrum Validation... 5
Test II System Stability 8
Test III Instrument Detection Limit 8
Test IV Saturation Recovery. 11.
Test V Precision.... 12
Test VI Library Search 16
Test VII Quantitative Analysis .with Liquid-Liquid Extraction 17
Test VIII Quantitative Analysis with Inert Gas Purge and Trap 19
Test IX Qualitative Analysis with Real Samples 27
Test X Solid Probe Inlet System . 30
^ 4. References 32
v.
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FIGURES
Number
Page
1 Control chart for nitrobenzene in reagent water 21
2 Control chart 'for pyrene in reagent water 22
TABLES
Number Page
1 Suggested GC Columns and Conditions . 7
2 Decafluorotriphenylphosphine Key Ions and Ion Abundance 7
Criteria
3 Ions Over 3% Relative Abundance Observed in the 70 ev Mass
Spectrum of DFTPP . 10
4 Common Background Ions in GC/MS Systems 11
5 Precision Statistics for Ten Priority Pollutants Plus
Octadecane 13
i
6 Precision Statistics Using an Internal Standard 15
7 £-Bromofluorobenzene Key Ions and Ion Abundance Criteria 16
8 Precision and Accuracy Data for Liquid-Liquid Extraction
with GC/MS and an External Standard 20
9 Method Efficiencies for Some Priority Pollutants Plus
£-Bromof 1 uorobenzene 25
10 Precision and Accuracy Data for the Purge and Trap Analysis
with GC/MS and an External Standard 26
11 Precision and Accuracy Data for the Purge and Trap Analysis
with GC/MS and the Internal Standard jD-Bromofluorobenzene 28
12 Precision and Accuracy Data for the Purge and Trap Analysis
with GC/MS and the Internal Standard Dibromochloromethane 29
VI
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ACKNOWLEDGMENT
The authors wish to acknowledge the careful and competent technical
assistance of William Middleton, Jr., who has performed all of the GC/MS
tests described in this report at least once, and several of them hundreds
of times.
A number of Environmental Protection Agency personnel reviewed the first
draft of this report, and many provided written comments which substantially
assisted the authors in the preparation of this document. Our deep
appreciation is due to all of the following:
William Andrade
Region 1
Surveillance and Analysis Division
Lexington, MA 02173
Thomas A. Beliar
Environmental Monitoring and
Support Laboratory
Cincinnati, OH 45268
Robert L. Booth, Deputy Director
Environmental Monitoring and
Support Laboratory
Cincinnati, OH 45268
Aubry E. Dupuy, Jr.
Pesticides Monitoring Laboratory
Bay Saint Louis, MS 39520
Robert D. Kleopfer
Region 7
Surveillance and Analysis Division
Kansas City, KS 66115
John Logsdon
National Enforcement
Investigation Center
Denver, CO 80225
Dwight G. Ballinger, Director
Environmental Monitoring and
Support Laboratory
Cincinnati, OH 45268
Joseph N. Blazevich
Region 10
Surveillance and Analysis Division
Manchester, WA 98353
Herbert J. Brass
Division of Technical Support
Cincinnati, OH 45268 ,
Denis Foerst
Environmental Monitoring and
Support Laboratory
Cincinnati, OH 45268
John Kopp
Environmental Monitoring and
Support Laboratory
Cincinnati, OH 45268
E. William Loy, Jr.
Region 4
Surveillance and Analysis Division
Athens, GA 30601
vn
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John M. McGuire
Environmental Research Laboratory
Athens, 6A 30601
Aaron A. Rosen
Cincinnati Water Works
Cincinnati, OH 45228
D. C. Shew
R. S. Kerr Environmental
Research Laboratory
Ada, OK 74820
Alan Stevens
Municipal Environmental
Research Laboratory
Cincinnati, OH 45268
Curt Norwood
Environmental Research Laboratory
Narragansett, RI 02882
Dennis R. Seeger
Municipal Environmental
Research Laboratory
Cincinnati, OH 45268
Clois Slocum
Municipal Environmental Research
Laboratory
Cincinnati, OH 45268
Emilio Sturino
Region 5
Surveillance and Analysis Division
Chicago, IL 60606
The second draft was reviewed by the following, and we are similarly
grateful for their very helpful written comments.
Joan T. Bursey
Research Triangle Institute
Research Triangle Park, NC 27709
Leonard F. Herzog
Nuclide Corporation
State College, PA 16801
Russell L. McAvoy
U.S. Geological Service
Denver, CO 80225
M. W. Siege!
Extranuclear Laboratories, Inc.
Pittsburgh, PA. 15238
Jim Stauffer
Arthur D. Little, Inc.
Cambridge, MA 02140
Kathy Thrun
Arthur D. Little, Inc.
Cambridge, MA 02140
John A. Winter
Environmental Monitoring
and Support Laboratory
Cincinnati, OH 45268
Edward M. Chait
E.I. DuPont DeNemours and Company
Wilmington, DE 19898
Philip L. Levins
Arthur D. Little, Inc.
Cambridge, MA 02140
David J. Munch
EPA Office of Drinking Water
Cincinnati, OH 45268
David E. Smith
Finnigan Corporation
Sunnyvale, CA 94086
Paul A. Taylor
California Analytical Laboratories,
Incorporated
Sacramento, CA 95814
Kenneth B. Tomer
Research Triangle Institute
Research Triangle Park, NC 27709
vm
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SECTION 1
INTRODUCTION
This report gives a series of performance tests to evaluate computerized
gas chromatography - mass spectrometry (GC/MS) systems. These tests were
designed for general use, and are applicable to all types of GC/MS systems.
All of the tests use the continuous, repetitive measurement of spectra
method of data acquisition, and no selected ion monitoring tests are
included. Except for the spectrum validation test (Test I), these
performance tests are not intended for routine application in a quality
assurance program. Test I is a required daily quality control test for
GC/MS systems in routine use for measurements of organic compounds in
environmental samples. The other performance tests are intended for use in
the evaluation of new GC/MS systems before purchase, or after the completion
of the manufacturer's installation. These tests are also useful to evaluate
GC/MS performance after a long period of downtime for extensive maintenance
or repair, after a long period of equipment neglect or non-use, or as
general training experiments for GC/MS operators. Several of the tests go
beyond equipment performance and may be used to evaluate the performance of
laboratories using GC/MS for organics analysis.
The performance tests described in this report are more rigorous and
extensive than the typical manufacturer's installation tests. Indeed, this
was intended, and the emphasis of the tests is on an evaluation of the total
operating system in a rigorous way using experiments that closely resemble
real, day-to-day operating situations. The performance tests should be
conducted in the order given, but several are optional or depend on the
availability of certain accessories, e.g., the solid probe inlet test.
All the tests described in this report require an operator, and some
depend heavily on the skills of laboratory personnel. Therefore, the
results of some tests may be limited by the skills available in the
laboratory. An experienced, two-person team consisting of a professional
scientist and a technician will require approximately three weeks to
complete the equipment tests assuming there are no major hardware or
software problems. Inexperienced teams or individuals may require anywhere
from six weeks to one year to complete all the tests, especially if major
hardware or software problems develop. In these tests, the operator and
other laboratory personnel are a crucial part of the total operating system.
The examples given in this report reference packed column gas chromatog-
raphy, but the tests described are equally applicable to open tubular GC/MS
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systems. With open tubular (capillary) systems some minor adjustments in
operating conditions may be necessary.
For all the tests it is assumed that the manufacturer has provided
acceptable documentation of users instructions for the operation and
maintenance of the GC/MS system. At the very minimum this must include
clearly written descriptions of all operating and test functions, clear
descriptions of all commands used in the operation of the data system,
examples of all commands, and intelligible documentation of error messages.
Examples of all outputs must be included as well as error recovery
procedures. There must be a narrative description of all data system files,
and the narrative should describe the exact nature of the algorithm used for
all the significant mass spectrometric processes. The maintenance manuals
must include a complete set of hardware engineering drawings, and
maintenance must be described in terms of block diagrams, logic diagrams,
flow charts, circuit descriptions, and parts lists.
It is also assumed that the laboratory has provided the GC/MS facility
with an appropriate environment including air conditioning and other
utilities as required, trained management and operating personnels needed
supplies, essential support equipment, and a reasonable amount of working
space which allows access at the sides and rear of the system for
maintenance.
Finally, a system logbook must jbe maintained throughout the evaluation
period. This must include an entry for every working day noting the status
of the system. This entry must be imade even if the system is not used on
that day, and signed by the responsible person. The logbook must include a
complete record of the number of gas chromatographic injections per day, the
number of solid probe samples, all chromatographic column changes, all
maintenance procedures, all requirements for service from the manufacturer,
and each entry must be signed and dated. This information must be
summarized in the performance evaluation report, and the mean numbers of gas
chromatographic injections and solid probe samples before ion source
maintenance (cleaning) must be reported.
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\
I.
II.
Ill,
IV.
V.
VI.
VII,
SECTION 2
&JMMARY OF PERFORMANCE TESTS
V
Spectrum Validation Test* ~ Uses decafluorotriphenyl phosphine (DFTPP)
to determine whether the'.system gives a 70 ev electron ionization
fragmentation pattern sinn lar to that found in the historical mass
spectrometry data base, and-the required mass resolution and natural
abundance isotope patterns. \The spectrum of DFTPP must meet the
criteria given in Table 2. \
System Stability Test - Uses DFT»9P to test moderate term (20-28 hours)
system stability. The criteria gSJven in Test I must be met.
Instrument Detection Limit Test - Ustfs DFTPP to measure the full and
valid spectrum detection limit at a defined and tolerable chemical
noise level. At a signal/noise = 5, t^e required instrument detection
limits are at least 50 nanograms for systems used in the analysis of
industrial or municipal wastes, and at le^st 30 nanograms for systems
used in the, analysis for ambient or drinking water.
Saturation Recovery Test - Uses DFTPP and ^-bYomobiphenyl to simulate
a frequently encountered situation with real samples. The spectrum of
DFTPP, measured within two minutes after the election of a 250 fold
excess of £-bromobiphenyl, must not contain significant contributions
from the ions attributable to £-bromobiphenyl. \
Precision Test - Uses a variety of typical environmental pollutants to
determine precision from filling a syringe to peak integration. The
mean relative standard deviation for the compounds used,in the test
which elute as narrow peaks must be 7% or less using either peak areas
in arbitrary units or ratios of peak areas. For broad peaks the mean
relative standard deviation must be 13% or less.
.Library Search Test - Uses data from Test V to evaluate the speed and
completeness of the minicomputer library search algorithm. Th«? mean
search time, including background subtraction, must be one minute or
less, and all test compounds must be identified as most probable
except isomers with very similar spectra should not be counted as
incorrect.
Quantitative Analysis with Liquid-Liquid Extraction - Uses a variety
of environmental pollutants to measure quantitative accuracy and
3
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precision of the total analytical method. The grand average of the
percentages of the true values observed must be in the 68-132% range
with a mean relative standard deviation of 38% or less using either
internal or external standards. This test also evaluates laboratory
performance.
VIII. Quantitative Analysis with Inert Gas Purge and Trap - Uses a variety
of compounds to measure quantitative accuracy and precision of the
total analytical method. The grand average of the method efficiencies
must be 70% or more, and all; compounds must exceed 30% efficiency.
The spectrum of _p_-bromofluor|o- benzene must meet the criteria given in
Table 7. The grand average |of the percentages of the true values
observed must be in the range of 90-110% with a mean relative standard
deviation of 19% or less using either internal or external standards.
i
IX. Qualitative Analysis with Real Samples - Uses a real sample to
evaluate the ability of the [system to deal with real sample matrix
effects and interferences. 'All compounds must be correctly identified
except isomers with nearly identical mass spectra should not be
counted as incorrect. This !test also evaluates laboratory performance.
X. Solid Probe Inlet System Test (Optional) - Uses cholesterol to
evaluate the spectrum validijty achievable with a solid probe inlet
system. The spectrum of cholesterol must meet the criteria given in
step three of the test.
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SECTION 3
EXPERIMENTAL PROCEDURES
I. Spectrum Validation Test
Correct identifications of organic pollutants from gas chromatography
mass spectrometry (GC/MS) data require valid mass spectra of the compounds
detected. This is prerequisite to the interpretation of the spectra, i.e.,
either an empirical search for a match within a collection of authentic
spectra or an analysis from the principles of organic ion fragmentation. A
properly operating and well tuned GC/MS :is required to obtain valid mass
spectra.
The purpose of this test is to make a quick check - about 15 minutes -
of the performance of the total operating system of a computerized GC/MS.
Thus with a minimum expenditure of time, an operator can be reasonably sure
that the GC column, the enrichment device, the ion source, the ion separa-
ting device, the ion detection device, the signal amplifying circuits, the
analog to digital converter, the data reduction system, and the data output
system are all functioning properly.
An unsuccessful test requires, of course, the examination of the
individual subsystems and correction of the faulty component. Environmental
data acquired after a successful systems check are, in a real sense, vali-
dated and of far more value than unvalidated data.. Environmental data
acquired after an unsuccessful test may be worthless and may cause erroneous
identifications.
It is recommended that the test be applied at the beginning of a work
day on which the system will be used and also anytime there is a suspicion
of a malfunction. A mass spectrometer which meets the criteria of this test
will, in general, generate mass spectra pf organic compounds which are very
similar, if not identical, to spectra in collections and textbooks which
have been developed over the years with other types of spectrometers. If
the performance criteria of this test cannot be met by the user, the system
is unacceptable for general purpose environmental measurements.
Procedure:
1. Make up a stock solution of decafluorotriphenylphosphine (DFTPP)
at one milligram per milliliter (1000 ppm) concentration in
acetone (or a hydrocarbon .solvent). The reference compound used
in this test is available from PCR, Inc., P. 0. Box 1778,
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Gainesville, Florida, 32602 and may be named bis(perfluorophenyl)
phenylphosphine. This stock solution was shown to be 97+% stable
after six months and indications are that it will remain usable
for several years. Dilute an aliquot of the stock solution to 10
micrograms per milliliter (10 ppm) in acetone. The very small
quantity of material present in very dilute solutions is subject
to depreciation due to adsorption on the walls of the glass
container, reaction with trace impurities in acetone, etc.
Therefore, this solution will be usable only in the short term,
perhaps one week.
2. Select a GC column for the tests. Any column that elutes DFTPP in
a reasonable time may be used, and several suggested columns are
listed in Table 1. Parameters should be adjusted to permit at
least four mass scans during elution of the DFTPP. This will
permit selection of a spectrum that is reasonably free of
abundance distortions due to rapidly changing sample pressure.
3. Set the preamplifier to a suitable sensitivity and set the
baseline threshold (zero instrument). Mass scale calibration is
optional depending on the stability of the system — see the last
paragraph of this test.
4. Prepare for data acquisition with the following variables:
8.
9.
Mass Range:
Scan Time:
Electron Energy:
Electron Multiplier:
40-450 amu
approximately 2 to 5 seconds
70 ev
Not to exceed that recommended by the
supplier for the age of the device.
5. Inject with a syringe 50 inanograms (five micro!iters) of the
dilute standard into the GC column. Make appropriate concentra-
tion adjustments if an open tubular column is being used.
6. After the acetone elutes from the column and is pumped or diverted
from the system, turn on the ionizer and start scanning.
7. Terminate the run after the DFTPP elutes, and plot the total ion
current profile.
Select a spectrum number on the front side of the GC peak as near
the apex as possible, select a background spectrum number
immediately preceding the peak, and display the background
subtracted spectrum. Some data systems permit spectrum averaging
to minimize variations in ion abundance due to rapidly changing
sample pressure. This option is acceptable, and may be required
for narrow peaks from open tubular columns.
The mass spectrum can be output in various ways including a plot
of the full spectrum on the plotter or cathode ray tube or a print
of the full spectrum on a printer or cathode ray tube.
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TABLE 1. SUGGESTED GC COLUMNS AND CONDITIONS
Dimension (Type) Packing
2m x 2 mm ID
(Glass)
2m x 2 mm ID
(Glass)
2m x 2 mm ID
2m x 2 mm ID
(Glass)
30m x .25mm ID
(Glass)
1.95% QF-1 plus
1.5% OV-17 on
80/100 mesh Gas-Chrqm Q
3% OV-1 on 80/100
mesh Chromosorb W
5% OV-17 on 80/100
mesh Chromosorb W
1% SP2250 on 100/120
mesh Supelcoport
Wall coated SP 2100
Flow Rate
30 ml/min
30 ml/min
30 ml/min
30 ml/min
2-5 ml/min
220
220
170
R. Time
4 min
5 min
5 min
5 min
40,240 10 min
The spectrum obtained on the test system must meet the criteria given for
the key ions in Table 2 (1).
If the relative abundances are not within the limits specified, the
appropriate adjustments must be made, i.e., resolution, source potentials,
calibration of the mass scale, source magnet position, etc. The manufac-
turer may need to be consulted for assistance in this adjustment. Repeat
this test until satisfactory results are obtained. If computer controlled
tuning is used but manual adjustments are required to meet these criteria,
this should be noted in the evaluation.report.
TABLE 2. DECAFLUOROTRIPHENYLPHOSPHINE KEY IONS AND ION ABUNDANCE CRITERIA.
Mass
51
68
70
127
197
198
199
275
365
441
442
443
Ion Abundance Criteria
30-60% of Mass 198
Less than 2% of Mass 69
Less than 2% of Mass 69
40-60% of Mass 198
Less than 1% of Mass 198
Base Peak, 100% Relative Abundance
5-9% of Mass 198
10-30% of Mass 198
At least 1% of Mass 198
Present, but less than Mass 443
Greater than 40% of Mass 198
17-23% of Mass 442
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II. System Stability Test
The purpose of this test is to evaluate moderate term system stability.
Repeat the test described in Section I after 20-28 hours. Do not make any
adjustments or recalioration of the isystem between tests except routine
overnight procedures. The abundance criteria in Table 2 must be met. If
these criteria are not met, the system is too unstable for routine use and
must be repaired.
III. Instrument Detection Limit Test
This test is to determine the smallest quantity of standard test
material that can be injected into the GC/MS system that gives an acceptable
spectrum meeting the criteria in Table 2, but has a sufficiently low level
of background signals to allow correct interpretation of that spectrum if
the sample was an unknown. Background signals are defined as mainly
chemical noise that is not subtracted effectively by the background
correction program. A spectrum of a test compound contaminated with
background signals to the extent of about 10% or more of its total ion
abundance is considered to be difficult to interpret correctly. It may be
possible to find a target compund's Ispectrum in such a situation, but this
does not constitute an interpretation of an unknown spectrum as used here.
There is some variability in the 10% criteria because background distributed
among a large number of small ions may be acceptable, but a distribution
among a few large ions will be unacceptable. Therefore, a signal to
chemical noise ratio based on a selection of six ions is used to evaluate
the detection limit. This also allows a relatively simple calculation of
the ratio.
In a GC/MS system there are a number of potential sources of background
signals (chemical noise) including septum bleed, stationary phase bleed,
vacuum system background from various physical components, and ion source
contamination. Furthermore, all signals are dependent on GC column
efficiency, enrichment device efficiency, vacuum system efficiency, lomza-
tion efficiency, ion transmission efficiency, and detector gain. Therefore,
this test is highly sensitive to the specific system configuration (specific
GC column, etc.) and the current condition of that system, e.g., condition
of the GC column, extent of contamination in the ion source, extent of
contamination of the quadrupole rods if a quadrupole instrument, and
condition of the electron multiplier. The state of the system should be
documented as part of the records of the instrument detection limit test.
Procedure:
1. Make four dilutions of the stock solution of DFTPP described in Test
I. The dilutions should have the concentrations of ten micrograms
per milliliter, five micrograms per milliliter, one microgram per
milliliter, and one-tenth of a microgram per milliliter. Other
concentrations are acceptable and may be required for open tubular
columns.
2. Follow the basic procedures given in Test I and make the following
8
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series of injections (other sequences may be used, these are
examples):
Amount Injected
50 nanograms
20 nanograms
10 nanograms
5 nanograms
1 nanogram
100 picograms
Volumes and Standards
5 ul of 10 ug/ml standard
4 ul of 5 ug/ml standard
2 ul of 5 ug/ml standard
1 ul of 5 ug/ml standard
1 ul of 1 ug/ml standard
1 ul of 0.1 ug/ml standard
3. List the masses and relative abundances of the background subtracted
spectra of DFTPP. Subtract the background spectra as described in
Test I. If necessary use an extracted ion current profile to locate
the GC peak. Discard all spectra that do not meet the criteria in
Table 2. If additional dilutions or measurements are necessary, do
them.
4. For each of the remaining spectra compute the ratio R as follows:
DFTPP
R =
BACK6D
where:
DFTPP = the summation of the relative abundances of the ions at
masses 127, 255, 275, 441, 442 and 443
BACK6D = the summation of the relative abundances of the six most
abundant non-DFTPP background ions. Background ions with less
than 3% relative abundance are assigned a value of 3. If all
background is less than 3% relative abundance, this term is 18.
Table 3 contains all DFTPP ions over 3% relative abundance and
Table 4 contains a group of common background ions.
Prepare a plot of R values as a function of amount injected. The
instrument detection limit defined in this test is for the complete,
valid spectrum with a defined level of acceptable noise. This
detection limit is the amount injected that gives an R value of
five. If sufficient points are available, a good estimate of the
instrument detection limit may be obtained from a first or second
order regression on this data.
The rationale for the selection of an R value of five is consistent
with the previous statement that background ions should be less than
about 10% of the total ion abundance in an interpretable spectrum.
The average relative abundance of the six DFTPP ions used to compute
R is in the 25-35% range. For an R value of five the average
relative abundance of the six background ions will be in the 5-7%
range, and it is estimated that all background ions under these
conditions will be less than 10% of the total ion abundance.
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TABLE 3. IONS OVER 3% RELATIVE ABUNDANCE OBSERVED
IN THE 70 ev MASS SPECTRUM OF DFTPP
AMU
50.0
51.0
69.0
74.0
75.0
77.0
78.0
93.0
99.0
107.0
110.0
117.0
127.0
128.0
129.0
167.0
168.0
186.0
187.0
198.0
199.0
205.
206.
207.
217.0
221.0
224.0
227.0
244.0
255.0
256.0
274.0
275.0
276.0
296.0
423.0
441.0
442.0
443.0
.0
.0
.0
INTENSITY
[
8.11
34.60
32.93
3.10
4.53
34.84 -
3.10
3.10
3.81
10,97
20.76
6.44
37.70
3.10
12.88
4.05
4.77
13.12
3.81
100.00
7.
5.
,15
.01
20.28
4.53
5.01
4.29
11.21
.81
11
3.
8.
49.16
.39
.29
7.
4.
23.15
81
01
34
9.30
69.45
12.88
PERCENT OF TOTAL INTENSITY
1.11
4.74
4.51
0.42
0.62
4.77
0.42
0.42
0.52
.50
.84
0.88
5.16
0.42
1.76
0.55
0.65
1.79
0.52
13.69
0.98
0.68
2.77
0.62
0.68
0.58
1.53
0.52
1.11
6.73
1.01
0.58
3.17
0.52
0.68
0.45
1.27
9.51
1.76
10
-------
TABLE 4. COMMON BACKGROUND IONS IN GC/MS SYSTEMS
Masses
41,43,55,57,
69,71,81,83,
85,95,97,99
149
73,, 101,135,197,207
259,345,346,355
169,261
Sources
Saturated hydrocarbons and
unsaturated hydrocarbons -
cyclic and open chain-many sources
Phthalate esters used as plasticizers
in tubing, etc.
Methyl and phenyl silicone
polymers used in stationary
phases, diffusion pump oil, etc.
Polyphenyl ether diffusion
pump oil
The required instrument detection limits, at an R value of five, are 50
nanograms for systems used in the analyses of industrial or municipal
wastes, and 30 nanograms for systems used in analyses of ambient or drinking
waters. These limits were obtained from considerations of EPA recommended
sample sizes and concentration factors. If a system cannot meet these
criteria, maintenance or repair is required. Particular attention should be
given to those items mentioned in the second paragraph of this test.
Observed detection limits with this test are as follows:
1. A Finnigan 3200 equipped with a Varian 1400 GC, a packed 1% SP 2250
Column (Table 1), a Systems Industries RIB interface, and a PDP-8
datasystem (disk) gave a detection limit of five nanograms.
2. A Finnigan 4000 with a Finnigan 9610 GC, a packed 1% SP 2250 column
(Table 1), an INCOS interface, and an INCOS datasystem (Nova 3, disk)
gave a detection limit of 25 nanograms.
IV. Saturation Recovery Test
The purpose of this test is to evaluate the ability of a system to
measure the spectrum of a test compound at a low level immediately after a
relatively large quantity of another compound entered the system. This
situation occurs frequently in real environmental samples, especially waste
samples where a very large concentration of one component may saturate the
detector, and within a few minutes or less a very small quantity of a
compound of interest may enter the detector.
Procedure:
1. Prepare an acetone solution containing five milligrams per milliliter
of £-bromobiphenyl and 20 micrograms per milliliter of DFTPP. A
second solution containing approximately 50 micrograms per milliliter
11
-------
of each is optional and may be useful to optimize chromatographic
conditions. ;
2. Establish GC conditions such that the DFTPP elutes within two minutes
after the elution of the £-bromobiphenyl. These conditions were
achieved with a 6' x 2 mm ID' glass column packed with 1% SP2250 on
Supelcoport (100/120 mesh) using a flow of 30 ml of helium per minute
with the initial column temperature at 120°C and programming to
230°C at 10° per minute. The ]3-bromobiphenyl eluted at 110
seconds and the DFTPP at 210 seconds. This test is carried out using
the same basic operating parameters given in Test I.
3. Inject two microliters of the standard solution containing the 250:1
ratio of £-bromobiphenyl to JDFTPP. Plot the DFTPP spectrum as in
Test I. Each of the ions at! masses 152, 232, and 234, which are the
three most abundant in the spectrum of £-bromobiphenyl, must be below
5% relative abundance in the| background subtracted spectrum of DFTPP.
I
V. Precision Test
The purpose of this test is to measure the precision of the GC/MS system
in quantitative analysis using continuous, repetitive measurement of spectra.
This test evaluates precision fromjfilling a syringe to integration of the
peak area for a specific quantisation ion. The entire test should be
carried out on the same day by the isame technician. The application of an
automatic sample changer in this test is required if it will be used for
normal sample processing. This shcjuld be documented in the test results.
If acceptable precision cannot be obtained with this test, the precision of
a complete anaytical method may also be unacceptable.
j
Procedure:
1. Select a group of seven or more compounds, and prepare a standard
solution in acetone that contains the entire group. Some recommended
compounds are in Table 5, and the concentration of each should be 20
micrograms per mi Hi liter. !This group of compounds must include a
chlorinated hydrocarbon that may decompose on a hot metal surface and
a polycyclic aromatic hydrocarbon with a molecular weight greater
than 200. For compounds amenable to the inert gas purge and trap
procedure, prepare the standard solution in methanol at the same
concentration. The purge arid trap mixture must include chloroform,
bromoform, sym-tetrach1oroethane, and p-bromofluorobenzene. Some
recommended compounds are in Tables 9-12. This test may be conducted
with either or both groups of compounds.
12
-------
TABLE 5. PRECISION STATISTICS FOR TEN PRIORITY POLLUTANTS PLUS OCTADECANE
COMPOUND
1,3-DICHLOROBENZENE
NAPHTHALENE
1,2,4-TRICHLOROBENZENE
n-OCTADECANE
DIMETHYL PHTHALATE
DI-ji-BUTYL PHTHALATE
N-NITROSODIPHENYLAMINE
HEXACHLOROBENZENE
PYRENE
CHRYSENE
BENZO(A)PYRENE
:GRATION
MASS
146
128
180
254
163
149
169
284
202
228
252
PEAK1
TYPE
N
N
N
N
N
;N
N
N
N
B
B
MEAN
AREA
6771
18077
5412
345
13540
21770
6460
4027
18107
10345
9518
(S/MEAN .
S *100
278
375
195
15
501
364
228
139
607
636
681
4.1
2.1
3.6
4.2
3.7
1.7
3.5
3.4
3.4
6.2
7.2
= narrow; B = broad (see text for definitions)
Select an appropriate GC column. For compounds similar to those in
Table 5, the columns in Table 1 are satisfactory. For compounds,
amenable to purge and trap procedures, two acceptable columns are an
8 ft. stainless steel or glass column packed with 1% SP-1000 coated
on 60/80 mesh Carbopack B or packed with 0.2% Carbowax 1500 coated
on 60/80 mesh Carbopack C. Prepare for data acquisition with the
following variables:
mass range: 35-350 amu (For purge and trap compounds use 20-260 amu)
scan time: approximately two to six seconds (two or three seconds
with open tubular columns)
electron energy: 70 ev
electron multiplier: not to exceed that recommended by the
supplier for the age of the device.
Inject with a syringe or automatic sample changer four micro! iters
(80 nanograms of each compound) of the standard solution and acquire
data until all compounds have eluted from the column. Save the data
13
-------
4.
file on the data system and repeat the injection a minimum of four
times, saving the data files in each case.
Plot the total ion current profiles, and use a quantisation program
to integrate peak areas in arbitrary units (usually
analog-to-digital counts) over a specific quantisation mass for each
compound in each data file. ! Precision may be evaluated using either
the peak areas in arbitrary Units or ratios of peak areas. The
former gives a precision representative of external standardization,
and the latter a precision representative of internal
standardization. There willlbe no significant difference in the
results using the two methods if the system is operating properly
and acceptable syringe filling and injection techniques are used.
It is recommended that calculations be carried out using both
methods for comparison of results, but the minimum requirement is
that precision be evaluated Using the method that corresponds to the
standardization procedure used in the laboratory for environmental
samples. '
Table 5 is an example of data from five replicate syringe injections
of 80 nanograms of each compound using a Finnigan 3200 and a PDP-8
based data system. The mean areas are in analog-to-digital
converter units and the standard deviations (S) were computed using
the equation below. The last column in Table 5 is the relative
standard deviation which is (S/mean area)* 100. Table 6 contains
the results of computations with exactly the same raw data as in
Table 5, but using ratios of areas as in internal standard
calibrations. The response factor (RF) is defined in test VII, and
the mean response factors are shown in Table 6. The compound
di~n-butylph thai ate was selected as the internal standard because it
showed the smallest variation in peak area (1.7%, Table 5) and
eluted near the mid-point in the chromatogram. The standard
deviations and relative standard deviations were computed as in
Table 5.
N
N
S =
N :€Area . - ( ^ Area.)'
1=1 1 i=l n
N (N-l)
where :
S = the standard deviation
N = the number of measurements
for each compound
Area = the integrated ion abundance of the
quantisation mass
The compounds designated as having narrow peak types in Tables 5 and 6
had widths at half height of 45 seconds or less. The mean relative standard
14
-------
TABLE 6. PRECISION STATISTICS USING AN INTERNAL STANDARD
COMPOUND
1,3-DICHLOROBENZENE
NAPHTHALENE
1,2,4-TRICHLOROBENZENE
Jl-OCTADECANE
DIMETHYL PHTHALATE
DI-n-BUTYL PHTHALATE
N-NITROSODIPHENYLAMINE
HEXACHLOROBENZENE
PYRENE
CHRYSENE
BENZO(A)PYRENE
INTEGRATION
MASS
146
128
180
254
163
149
169
284
202
228
252
PEAK1
TYPE
N
N
N
N
N
N
N
N
N
B
B
MEAN
RF
0.3112
0.83048
0.2486
0.0158
0.62202
1.00000
0.2968
0.1850
0.83171
0.4751
0.4370
(S/MEAN
S *100
0.01512
0.017250
0.008571
0.000838
0.022980
0.00000
0.01008
0.005899
0.023110
0.02619
0.0275
4.9
2.1
3.4
5.3
3.7
0
3.4
3.2
2.8
5.5
6.3
15
-------
deviation for the data in Table 5 is|3.3%, and the corresponding mean from
Table 6 is 3.6 %. Therefore there wpis no significant difference in the
precision of external and internal standardization. The requirement of this
test is that the mean relative standard deviation of data from narrow peaks
be 7% or less. This requirement is based on the general observation that
data from inter laboratory comparisons is usually about a factor of two more
variable than single laboratory data, and this is a reasonable requirement
for an acceptable system.
The last two compounds in Tables 5 and 6 gave broader peaks with peak
widths at half height of more than 45 seconds. Measurements of these are
more variable because of the changing baseline during temperature
programming and other factors. The mean relative standard deviations from
Tables 5 and 6 are 6.7% and 5.9% respectively, and internal standardization
may have some slight advantage for these peaks but there are too few data
points to judge the significance of this. The requirement of this test is
that the mean relative standard deviation of data from broad peaks be 13% or
less. Again the rule of thumb on interlaboratory data was used to establish
this requirement.
If this test is conducted with compounds amenable to the inert gas purge
and trap procedure, the compound £-bromofluorobenzene must be included in
the mixture. This compound is a secondary spectrum validation compound
which is used with GC columns that do not elute DFTPP. Therefore, after a
purge and trap column is installed for this test £-bromofluorobenzene may be
used as a daily check on spectrum validity. The ion abundance criteria for
£-bromofluorobenzene are in Table 7, and these are consistent with the DFTPP
criteria in Table 2.
TABLE 7. £-BROMOFLUOROBENZENE KEY IONS AND ION ABUNDANCE CRITERIA
Mass Ion Abundance Criteria
50
75
95
96
173
174
175
176
177
VI. Library Search Test
Minimum requirements for the library search are the availability of the
EPA/NIH database which is distributed through the National Bureau of
Standards. The searchable database^may be a subset of the EPA/NIH database,
but the subset must contain at least 10,000 spectra of general and
environmental interest and the Chemical Abstracts Service (CAS) registry
numbers for each compound. Programs must be available to allow the operator
20-40% of the base peak
50-70% of the base peak
base peak, 100% relative
abundance
5-9% of the base peak
less than 1% of the base peak
greater than 50% of the base peak
5-9% of mass 174
greater than 50% of the base peak
5-9% of mass 176
16
-------
to submit background corrected spectra to the library search, and receive a
printed report of the search results. The spectra from one of the
experiments in Test V should be submitted to the library search system.
Each compound must be .identified as the most probable by the library search,
except isomers that may have very similar 70 ev El mass spectra should not
be counted as incorrect. The mean search time, including the time for
background subtraction, should be one minute or less. Printed reports
should include CAS numbers. During this test make several deliberate
typical operator errors, such as entry of an incorrect command and a
non-existent file name. The data system should respond with an intelligible
error message, and return to a logical continuation point.
VII. Quantitative Analysis with Liquid-Liquid Extraction
This test uses a variety of environmental pollutants to measure quanti-
tative accuracy and precision of the total analytical method, but without
the complications of real sample matrix effects. The test is designed for
laboratories that conduct quantitative analyses of water samples with GC/MS
using continuous repetitive measurement of spectra. Therefore, laboratories
dealing in other media should design a similar test based on some standard
reference material. The principal difference between this test and Test V,
the precision test, is the consideration of potential errors and variations
due to: (a) extraction of the compounds from a reagent water matrix; (b)
concentration of the extract to a small volume; and (c) standardization of
the measured areas in terms of the concentration of the original sample in
micrograms per liter. This is one of the tests that goes beyond equipment
performance, and may be used to evaluate the performance of laboratories
using GC/MS for organics analysis.
It is recommended that the same standard solution of seven or more
compounds that may have been prepared'for the precision test (Test V) be
used in this test since retention information is already available, and the
concentrations are in an acceptable range. However, new standards may be
used and the seven or more compounds should be at the 20 microgram per
milliliter level in acetone.
Procedure:
1. Add 250 microliters (five micrograms of each compound) of the mixed
standard solution in acetone to each of a minimum of five liters of
reagent water. This aqueous solution is called a laboratory control
standard (LCS). Set aside one additional liter of reagent water as
a reagent blank.
2. Carry out the extractions according to the established procedures
(2,3,4). The methylene chloride extract must be concentrated to 0.5
milliliter. The reagent blank should be measured first by itself,
and if significant contamination is found, correct the problems
before proceeding with this test. See the references cited above
for information on the interpretation of blanks.
17
-------
3.
4.
5.
Select an appropriate column (Test V), and prepare for data
acquisition using the GC/MS operating parameters given in Test V.
Inject four microliters of each of the concentrated extracts, and
obtain GC/MS data from each injection. Save all of the data files
from the minimum of five extracts. Quantisation may be accomplished
with either internal or external standardization. If an external
standard will be used, this is already prepared and is the solution
used to prepare the laboratory control standards. Inject two
microliters (40 nanograms) of the external standard and acquire data
using the same acquisition parameters.
If an internal standard will be used, add five microliters of a one
milligram per mi Hi liter solution of the internal standard to each
of the 0.5 milliliters of concentrated extract. This corresponds to
the addition of five micrograms of the internal standard in such a
way as to not significantly change the volume of the concentrated
extract. Inject four microliters of each extract as above and save
all data files. If an internal standard is used it will be
necessary to measure the response factors (RF) in a separate
experiment with standards (no extraction). The response factors are
computed with the following equation:
Area (X)
RF
where:
Amount (XJ
Area (Sj
Amount (S)
Area(X) = the peak area of the compound in
consistent units.
Amount (X) = the quantity of the compound injected
in consistent units.
Area (S) = the peak area of the internal standard in
consistent units.
Amount (S) = the quantity of internal standard
injectgd in consistent units.
Plot the total ion current profiles and use a quantisation program
to integrate peak areas in arbitrary units (usually
analog-to-digital converter counts) over a specific quantisation
mass for each compound in each data file. If an internal standard
was employed computations in terms of response factors are
acceptable.
Precision and accuracy is expressed in terms of the percentages of
the true values (P) measured |in the experiments and the statistical
variations in the data. The standard deviations (S) and the
relative standard deviations (S/mean P) *100, are computed as
described in Test 5. With an external standard P is computed as
follows:
18
-------
p _ area (concentrated extracts) *100
area (external standard)•
With an internal standard P is computed with the equation below
which assumes the response factors are defined as above:
p _ area (concentrated extract) *100
area (internal standard)*RF
Table 8 shows precision and accuracy data obtained for eight compounds
extracted from reagent water with methylene chloride and measured with GC/MS
using a single external standard. The GC/MS was a Finnigan model 3200 with
a PDP-8 based datasystem. One difference between the data in Table 8 and
the procedures described in this test is that the data in Table 8 represents
duplicate extractions and measurements at four different concentration
levels between 15-200 micrograms per liter for each compound. Figures 1 and
2 show control charts which contain all eight P values for each of two of
the compounds. This is a recommended method (5) of displaying precision and
accuracy data. Charts should be labelled as in Figures 1 and 2. General
experience shows that P values measured over a concentration range of one or
two orders of magnitude are often concentration independent within the
precision of the method.
The mean of the P values (grand average) in Table 8 is 84%. Therefore,
the requirement of this test is that the grand average P value of the
compounds used in this test must be in the range of 68-132%. Again, as in
Test V, the expectation is that multi-laboratory data will usually be about
a factor of two more variable than single laboratory data. The mean
relative standard deviation from Table 8 is 19%, and the requirement of this
test is that the mean relative standard deviation be 38% or less.
VIII. Quantitative Analysis with Inert Gas Purge and Trap
This test uses a variety of environmental pollutants to measure
quantitative accuracy and precision of the total analytical method, but
without the complications of real sample matrix effects. The test is
designed for laboratories that conduct quantitative analyses of water
samples with GC/MS using continuous repetitive measurement of spectra.
Therefore, laboratories dealing in other media should design a similar test
based on some standard reference material. The principal difference between
this test and Test V, the precision test, is the consideration of potential
errors and variations due to: (a) purging of the compounds from a reagent
water matrix; (b) trapping and desorption of the compounds; and (c)
standardization of the measured areas in terms of the concentration of the
original sample in micrograms per liter. This test is required to evaluate
purge and trap equipment that is delivered as an integral part of a GC/MS
system, or other purge and trap equipment that is interfaced to the GC/MS
system.
The series of experiments in this test is used to generate three key
pieces of information about purge and trap performance:
19
-------
TABLE 8. PRECISION AND ACCURACY DATA FOR LIQUID-LIQUID EXTRACTION
WITH GC/MS AND AN EXTERNAL STANDARD
COMPOUND
NITROBENZENE
1,2,3-TRICHLOROBENZENE
NAPHTHALENE
ACENAPHTHYLENE
N-NITROSODIPHENYLAMINE
FLUORANTHENE
PYRENE
n-BUTYLBENZYLPHTHALATE
INTEGRATION
MASS
123
180
128
152
169
202
202
206
MEAN
P
94
85
73
83
89
80
83
86
S
8.8
13
18
15
19
19
19
17
(S/MEAN P)
*100
9.4
15
25
18
21
24
23
20
20
-------
Compound: nitrobenzene
Range: 50 - 200jug/l
Method: extraction, CH2CI2
Relative standard deviation: 9%
Data acquisition : 35 - 400amu
Quantitation: mass 123, one
external standard
MEAN + 3S
§
CO
0)
1-
•*-
m
c
-------
Compound: pyrene
Range: 15 - 130^ig/l
Method: extraction, CH2CI2
Relative standard deviation: 23%
Data acquisition: 35 - 400 amy
Quantitation: mass 202, one
external standard
MEAN + 3S
ItW
130
120
110-
J
£100-
0
E 90-
•»-
0 80
-------
(a) Method efficiency for test compounds by comparison of the measured
quantity from syringe injection into the GC with the quantity
measured after purging, trapping, and desorptipn. Because of the
method of calibration used in the purge and trap procedure high
method efficiency as defined above is not necessary for acceptable
precision and accuracy. However, high method efficiency is required
for acceptable sensitivity, and low method efficiency will result in
unacceptable detection limits. Also in the case of real samples, a
low method efficiency combined with an unfavorable matrix effect
could render the method totally useless.
(b) Precision of the overall purge, trap, desorption, and GC/MS analysis.
(c) Accuracy of the overall purge, trap, desorption, and GC/MS analysis
in terms of the percentage of the true value found in laboratory
control standards.
All the above information may be obtained from the same set of data. It
is recommended that the same standard solution of seven or more compounds
amenable to purge and trap that was recommended for the precision test (Test
V) bt? used in this test since retention information may be already
avail av^le, and concentrations are in an acceptable range.' However, new
standards may be used, and the seven or more compounds should be at the 20
microgratfi15 per milliliter level in methanol. The purge and trap mixture
must incline chloroform, bromoform, sym-tetrachloroethane and
2-bromofluo)"°kenzene.
Procedure:
1. Select c?n Appropriate column (see Test V) and prepare for data
acquisition u'sing the GC/MS operating parameters given in Test V.
2. Add five micro Triers (100 nanograms of each compound) of the mixed
standard in roethartp] to each of a minimum of five aliquots of .
reagent water. A z£FP dead volume syringe is strongly recommended
for this transfer. Purge and trap samples may be 5 ml to 25 ml, but
5 ml is recommended for op*"^1"11 method efficiency. This aqueous
solution is called a laboratory control standard.
3. Carry out the purge and trap accon^Q9 to the established procedures
(2,3,4) at ambient temperature. A nt water blanK should be
,, eraure. rec
measured first and at occasional interval*0 detect instrument
contamination. If significant contamination^? found, correct the,_
problems before proceeding with this test. See":r?ferences C1'ted
above for information on the interpretation of
!
Purge, trap, desorb, and obtain GC/MS data from a minimum i^T-
laboratory control standards and save all the data files. At
the midpoint of the purge and trap analyses, inject with a sy
five microliters (100 nanograms of each compound) of the mixed
standard in methanol into the purge and trap GC column. A zero dead
23
-------
volume syringe is strongly recommended for this injection. Acquire
GC/MS data using the same acquisition parameters used for purge and
trap analyses.
5. Plot the total ion current profiles, and use a quantisation program
to integrate peak areas in arbitrary units (usually analog-to-
digital converter counts) oyer a specific quantisation mass for each
compound in each data file.
I
6. Method efficiency must be evaluated by comparing the measured areas
from direct GC injection with the corresponding areas from the
purge, trap, and desorption experiments. Internal standards cannot
be used for this evaluation because method efficiencies for various
compounds are not yet known 1, and comparable response factors cannot
be computed for direct injection and purge/trap/desorption.
Prepare a table similar to Table 9 which shows data obtained with a
Finnigan model 3200, a PDP-8 data system, and a Tekmar model LSC-1
purge and trap device with a 25 ml sample container. The equation
used to compute method efficiencies (E) is shown below. The minimum
requirement of this test is that the mean of the mean (grand
average) method efficiencies of the compounds used in this test be
70% or more and all compounds must be recovered with at least 30%
efficiency. Also the spectrum obtained from £-bromofluorobenzene
must meet the ion abundance criteria given in Table 7. If these
requirements cannot be met, the system is unacceptable for
quantitative analyses and needs repair or redesign. One critical
method variable that may be optimized is the purge gas flow rate.
area (after purge and trap)
area (direct injection)
*100
7. Precision and accuracy data1may be obtained by choosing one of the
experiments in the purge and trap set as a standard, and computing
the percentages of the true values (P) measured in the other
laboratory control standards. This is consistent with the standard
method of calibration used with the purge and trap method. The
experiment chosen as the standard may either be treated as an
external standard, or may be used to compute response factors for an
internal standard calibration. Table 10 shows the data from the
method efficiency determination recomputed by ignoring the direct
injection result, and using one of the purge and trap experiments as
an external standard. The equation used to compute the percentages
of the true values (P) is as follows:
P =
area (after purge and trap)
area (external standard)
*100
The standard deviation of P and relative standard deviation were
computed as described in Test V. The mean of the P values (grand
average) in Table 10 is 95% and the mean relative standard deviation
24
-------
TABLE 9. METHOD EFFICIENCIES FOR SOME PRIORITY POLLUTANTS
PLUS £-BROMOFLUOROBENZENE
INTEGRATION
COMPOUND MASS
CHLOROFORM
CARBON TETRACHLORIDE
BROMODICHLOROMETHANE
TRICHLOROETHYLENE
DIBROMOCHLOROMETHANE
BROMOFORM
TETRACHLOROETHYLENE
Sym-TETRACHLOROETHANE
£-BROMOFLUOROBENZENE
83
117
83
130
129
173
166
83
174
MEAN AREA
PURGE/TRAP
2883
2289
2925
1474
1572
1241
1737
1032
1542
AREA DIRECT
INJECTION
3001
2314
3280
1653
2343
2788
2102
3071
2200
MEAN METHOD
EFFICIENCY^)
96
99
89
89
67
45
83
34
70
25
-------
TABLE 10. PRECISION AND ACCURACY DATA FOR THE PURGE AND TRAP
ANALYSIS WITH GC/MS AND AN EXTERNAL STANDARD
COMPOUND
CHLOROFORM
CARBON TETRACHLORIDE
BROMODICHLOROMETHANE
TRICHLOROETHYLENE
DIBROMOCHLOROMETHANE
BROMOFORM
TETRACHLOROETHYLENE
Sym-TETRACHLOROETHANE
£-BROMOFLUOROBENZENE
INTEGRATION MEAN
MASS P
(S/MEAN P)
S *100
83
117 :
83 :
130
129
173
166
83
174
92
97
96
94
98
96
96
100
90
8.8
7.9
7.2
7.4
4.4
5.2
14
14
12
9.5
8.2
7.5
7-9
4.5
5.4
14
14
14
26
-------
is 9.4%. The requirement of,this test is that the grand average of
the P values of the compounds used in this test must be in the range
of 90-110%. This is based on the general rule, described in Test V,
that data from interlaboratory comparisons is usually about a factor
of two more variable than single laboratory data. The mean relative
standard deviation must be 19% or less on the same basis.
The percentages of the true values (P) may also be computed by
selecting one compound in the test mixture as an internal standard,
and using one of the purge and trap experiments to establish
response factors as defined in Test VII. The percentages of the
true values (P) in the other laboratory control standards are
computed as follows (the terms have the same meaning defined in Test
VII):
P =
area (x) * 100
area (s) *RF
Table 11 shows the method efficiency data recomputed with
2-bromofluorobenzene as the internal standard. Response factors were
established with the same purge andd trap experiment that was used as an
external standard for the computations in Table 10. Table 12 shows the same
data recomputed with dibromochloromethane as an internal standard. Again,
response factors were established with the same purge and trap experiment
that was used as an external standard for the computations in Table 10.
The internal standard calculations reveal that the percentages of the
true values observed and the relative standard deviations are a function of
the internal standard selected. The compound 2-bromofluorobenzene eluted
late in the chromatogram after temperature programming, and measurements of
it were more variable because of this and other factors. This is reflected
in the grand average of the P values from Table 11 of 108% and the mean
relative standard deviation of 12%. The compound dibromochloromethane
showed the least variation in the external standard data (Table 10) and is
an excellent internal standard. The grand average of the P values from
Table 12 is 97% with a mean relative standard deviation of 6.5%. This
illustrates that care must be exercised in the selection of an internal
standard because of the potentially significant impact on the observed
precision and accuracy. The individual P values may also be charted as in
Figures 1 and 2 to provide a graphic presentation of the data.
IX. Qualitative Analysis with Real Samples
The purpose of this test is to-evaluate the ability of the GC/MS system,
laboratory, and sample preparation methods to deal with natural background,
interferences, and sample matrices found in real environmental samples. The
test is limited to qualitative analyses because of the unpredictable
quantitatvie effects of the sample matrix. This is one of the tests that
goes beyond equipment performance, and it may be used to evaluate the
performance of laboratories using GC/MS for organics analysis. The test is
designed for laboratories that conduct qualitative analyses of water samples
with GC/MS using continuous, repetitive measurement of spectra.
27
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TABLE 11. PRECISION AND ACCURACY DATA FOR THE PURGE AND TRAP
ANALYSIS WITH 6C/MS AND THE INTERNAL STANDARD £-BROMOFLUOROBENZENE
COMPOUND
CHLOROFORM
CARBON TETRACHLORIDE
BROMODICHLOROMETHANE
TRICHLOROETHYLENE
DIBROMOCHLOROMETHANE
BROMOFORM
TETRACHLOROETHYLENE
j&m-TETRACHLOROETHANE
£-BROMOFLUOROBENZENE
INTEGRATION MEAN
MASS P
(S/MEAN P)
S *100
83
117
83
130
129
173
166 ;
83
174
103
108
107
105
110
108
107
112
100
13
12
12
12
11
12
13
19
0
13
11
11
11
10
11
12
17
0
28
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TABLE 12. PRECISION AND ACCURACY DATA FOR THE PURGE AND TRAP
ANALYSIS WITH 6C/MS AND THE INTERNAL STANDARD DIBROMOCHLOROMETHANE
COMPOUND
CHLOROFORM
CARBON TETRACHLORIDE
BROMODICHLOROMETHANE
TRICHLOROETHYLENE
DIBROMOCHLOROMETHANE
BROMOFORM
TETRACHLOROETHYLENE
Sym-TETRACHLOROETHANE
£-BROMOFLUOROBENZENE
INTEGRATION
MASS
83
117
83
130
129
173
166
83
174
MEAN
P
94
98
98
95
100
98
98
101
92
S
5.8
4.3
3.7
3.8
0
2.0
9.8
11
9.7
(S/MEAN P)
*100
6.2
4.4
3.7
4.0
0
2.0
10
11
11
29
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Procedure:
1. Acquire appropriate quality control samples containing a number of
organic compounds dissolved in acetone, methanol, or other
water-miscible organic solvent and sealed in all-glass ampuls. The
concentration levels should be suitable for the preparation of
aqueous samples in the 10-500 microgram per liter range by addition
of one ml or less of the organic solution to the environmental
sample. Instructions for the dilutions should be supplied with the
samples, but the identity of the compounds in the ampuls should be
supplied separately to the laboratory management. A number of
samples of this type will be available in 1980 from:
Quality Assurance Branch
EMSL-Cincinnati
Environmental Protection Agency
Cincinnati!, Ohio 45268
i
2. Obtain an environmental sample typical of the type normally analyzed
in the laboratory. Add th£ quality control samples to the
environmental samples according to the instructions provided, and
proceed with the analyses using the appropriate method, e.g., as in
Tests VII and VIII.
3. Plot the total ion current profiles and identify all the compounds
using the mass spectra. All compounds must be correctly identified
except, as in the library search, isomers with nearly identical
70 ev electron ionization spectra should not be counted as incorrect.
X. Solid Probe Inlet System Test (optional)
The purpose of this test is to evaluate the critical thermal character-
istics of the solid probe inlet system, and to determine whether valid
spectra are produced with this system. The test uses cholesterol which is
sensitive to thermal effects. Data acquisition is by continuous repetitive
measurement of spectra.
Procedure:
1. Prepare a standard solution of cholesterol in acetone at a concen-
tration of 250 micrograms per milliliter. Evaporate one micro!iter
of this solution in the solid probe sample holder.
2. Use the data acquisition parameters given in Test I, and gradually
heat the sample until the cholesterol pressure increases and spectra
may be measured.
3. Terminate data acquisition and plot a background subtracted spectrum
of cholesterol as described in Test I. Measure the abundances of
the ions at masses 386 and 368, and compute the 386/368 abundance
ratio. This should be 3.0 or greater for an acceptable solid probe
inlet system. The ion abundance at mass 387 should be 26-34% of the
30
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abundance at mass 386. Finally large ions above 30% relative
abundance should be at masses 41, 43, 55, 57, 67, 69, 71, 79, 81,
83, 91, 93, 95, 105, 107, 109, 119, 121, 133, 145, 147, 149, 159,
161, 213, 275, 301, and 386.
31
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SECTION 4
REFERENCES
1. Eichelberger, J.W., L.E. Harris, and W.L. Budde, "Reference Compound to
Calibrate Ion Abundance Measurements In Gas Chromatography - Mass
Spectrometry Systems," Anal. Chem., 47, 995 (1975).
2. Budde, W.L., and J.W. Eichelberger, "An EPA Manual for Organics Analysis
Using Gas Chromatography - Mass Spectrometry," EPA Report No. EPA
600/8-79-006, March, 1979.
3. Budde, W.L., and J.W. Eichelberger, "Organics Analysis Using GC/MS," Ann
Arbor Science Publishers, Ann Arbor, Michigan, July 1979.
4. "Guidelines Establishing Test Procedures for the Analysis of
Pollutants," Federal Register,iVolume 44, No. 233, p. 69532-69552,
(December 3, 1979).
5. "Handbook for Analytical Quality Control in Water and Wastewater
Laboratories," EPA Report No. EPA-600/4-79-019, March, 1979, Chapter 6.
32
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/4-80-025
3. RECIPIENT'S ACCESSION'NO.
4. TITLE AND SUBTITLE
Performance Tests for the Evaluation of Computerized
Gas Chromatography/Mass Spectrometry Equipment and
Laboratories
5. REPORT DATE
April 1980 issuing date
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO.
William L. Budde and James W. Eichelberger
9. PERFORMING ORGANIZATION NAME AND ADDRESS
10. PROGRAM ELEMENT NO.
SAME AS BELOW
1BD884
11. CONTRACT/GRANT NO.
In-House
12. SPONSORING AGENCY NAME AND ADDRESS
Environmental Monitoring & Support Lab,
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
- Cinn, OH
13. TYPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE
EPA/600/06
15. SUPPLEMENTARY NOTES
16. ABSTRACT
A series of ten general purpose tests are described which are used to evaluate
the performance of computerized gas chromatography-mass spectrometry systems.
All of the tests use the continuous, repetitive measurement of spectra method
of data acquisition, and no selected ion monitoring tests are included.
Evaluation criteria are given with each performance test. Some of the tests
go beyond equipment performance, and may be used to evaluate the performance
of laboratories using GC/MS for organics analysis.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Mass Spectroscopy
Spectroscopic Analysis
Organic compounds
1402
0703
18. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (ThisReport)'
Unclassified
21. NO. OF PAGES
41
20. SECURITY CLASS (This page)
Unclassified
22. PRICE
_g£A Form 2220-1 (9-73)
33
* U.S. GOVERNMENT PRINTING OFFICE: 1980-657-146/5664
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