EPA-660/2-74-002
June 1974
Environmental Protection Technology Series
Evaluation of A Computer Program
For GC-MS Specific Ion Monitoring
National Environmental Research Center
Office of Research and Development
U.S. Environmental Protection Agency
Corvallis, Oregon 97330
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and
Monitoring, Environmental Protection Agency, have
been grouped into five series. These five broad
categories were established to facilitate further
development and application of environmental
technology. Elimination of traditional grouping
was consciously planned to foster technology
transfer and a maximum interface in related
fields. The five series ares
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
U. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ENVIRONMENTAL
PROTECTION TECHNOLOGY series. This series
describes research performed to develop and
demonstrate instrumentation, eguipment and
methodology to repair or prevent environmental
degradation from point and non-point sources of
pollution. This work provides the new or improved
technology required for the control and treatment
of pollution sources to meet environmental quality
standards.
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EPA-660/2-7^-002
June
EVALUATION OF A COMPUTER PROGRAM FOR
GC-MS SPECIFIC ION MONITORING
By
Ann L. Alford
Southeast Environmental Research Laboratory
College Station Road
Athens, Georgia 30601
Project #16ADN 27
Program Element #1BA027
National Environmental Research Center
Office of Research and Development
U. S. Environmental Protection Agency
Corvallis, Oregon 97330
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ABSTRACT
A computer program, "Specific-Ion Mass Spectrometric
Detection for Gas Chromatographic Pesticide Analysis" (SIM),
developed under an Environmental Protection Agency (EPA)
grant, was evaluated at the EPA's Southeast Environmental
Research Laboratory. Standard solutions of four chlorinated
pesticides were used to compare the SIM program data to those
produced by an existing limited-mass data acquisition program.
Under similar conditions, similar sensitivities were observed
with both programs. Greater sensitivity was obtained with
the SIM program when its parameter selection options were
fully utilized.
ii
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CONTENTS
Abstract ii
List of Figures iv
Sections
I Conclusions 1
II Introduction 2
III Experimental 5
IV Discussion 8
V References 18
VI Appendix 19
iii
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FIGURES
No. Page
1 SIM Program Initiation Dialogue 6
2 Plotter Output of SIM Data Obtained from 1,0
1 ng Each of Four Pesticides
3 Plotter Output of SIM Data Obtained from 11
0.2 ng Each of Four Pesticides
4 System/150 Data Obtained from a Solution 14
Containing 1 ng Each of Four Pesticides
5 SIM Data Obtained from 1 ng Each of Four 16
Pesticides When Three Mass Sets Were Used
iv
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SECTION I
CONCLUSIONS
With optimum conditions/ greater sensitivity was observed
with the Specific-Ion Monitoring (SIM) program data
acquisition than with System/150 limited-mass data acquisi-
tion. The SIM Program is useful for detection of trace
quantities of compounds whose fragmentation patterns are
known, but ions to be monitored must be carefully selected
to avoid background ions. If the compound's significant
ions are also background ions, the System/150 program is
preferable, because it permits background data subtraction.
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SECTION II
INTRODUCTION
Setting and enforcing water quality criteria, determining
the fate and effects of water pollutants, and developing
optimum control measures require the capability for identify-
ing specific organic pollutants. To be acceptable, the
identification technique must be highly specific since thou-
sands of compounds must be considered; Because some organic
compounds are toxic to aquatic organisms at concentrations
below 10 yg/1, the technique must also be sensitive.
One technique that has become invaluable in pollutant
analysis is gas chromatography-mass spectrometry (GC-MS) , a
method that utilizes a gas chromatograph to separate sample
constituents and a mass spectrometer to obtain mass spectra
as the sample components elute. A small dedicated computer
coupled to the GC-MS greatly decreases data reduction time.
A technique that increases sensitivity for GC-MS detection
of particular known compounds is limited-mass data acquisition.
The mass spectrometer, instead of being set to scan the entire
mass range, is set to monitor only a few significant mass
fragments of compounds suspected to be present in a sample.
By concentrating on only a few masses, specific ion monitor-
ing is more specific and 10- to 100-fold more sensitive than
standard repetitive scanning.
The masses of interest and appropriate GC conditions must be
known before specific mass data acquisition can begin.
Knowledge of the fragmentation pattern of a compound is not
adequate; ions to be monitored must be sufficiently unique
to provide definitive information. Some ions are indicative
of specific compounds; the presence of the ion and GC
retention data together can confirm a tentative identification.
Other ions indicate particular classes of compounds.
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Ions to be monitored must be carefully chosen to avoid
background ions such as those produced by column bleed and
pump oil and to be specific for the suspected compound.
With the dilute samples that require this special technique,
even a relatively insignificant background fragment can pro-
duce a stronger signal than the sample fragment being
monitored. Slight variations in background intensity may
then produce plotter pen displacements as large or larger
than those caused by sample ions.
The chosen ions must be sufficiently intense to provide
reasonable sensitivity. If more than one fragment is
monitored for a compound, the ratio of intensities provides
additional confirmatory information. Quantitation can be
achieved by comparing sample peak areas with those of
standards.
The repetitive-scanning standard data acquisition program of
System/150 could be used for limited-mass data acquisition
if the operator entered one or a few masses for each mass
range to be scanned and set a relatively long integration time
for each. However, some desirable features were not available
with the standard repetitive scanning program.
With the standard program, the masses had to be monitored in
ascending order. Program parameters could not be changed
without halting data acquisition and initiating another data
file. The standard program monitored the same set of ions
during the entire run, although the ions of interest changed
as different sample components eluted. Therefore, the
standard program had less sensitivity than could be obtained
with a program that permitted masses to be changed.
A program more suited to the specialized technique was
needed and was developed at Battelle Columbus Laboratories
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under Environmental Protection Agency Grant #R-800909. This
report summarizes the Southeast Environmental Research
Laboratory's evaluation of this program, Specific-Ion
Monitoring, and compares its performance to that of the
standard repetitive-scanning program.
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SECTION III
EXPERIMENTAL
INSTRUMENTATION
Mass spectral data were obtained with a Finnigan 1015 S/L
electron-impact quadrupole mass spectrometer operated with
the following conditions: 70eV electron energy, 10
sensitivity range, and 450 ya ionizing current. A modified
Varian 1400 gas chromatograph was interfaced to the mass
spectrometer with a Gohlke glass jet separator. The
chromatograph was fitted with a 6 ft x 0.25 in (O.D.) glass
column packed with 3% Silar on 80-100 mesh Gas Chrom Q.
The column was operated at 240° C isothermal with helium
flowing at approximately 18 ml/min. Data acquisition and
processing were controlled by System Industries System/150,
which interfaced the mass spectrometer with a 4K Digital
Equipment Corporation PDF 8/e computer.
SAMPLE PREPARATION
A stock solution containing four chlorinated pesticides
(o,p'-DDD, p,p'-DDE, p,p'-DDT, and dieldrin) was prepared by
dissolving 10 mg of each pesticide in 1£ of hexane. Aliquots
of the stock solution were diluted to give solutions with the
following concentrations: 5 ng/yJl, 1 ng/y&, 0.5 ng/yJl, and
0.2 ng/y&.
SIM PROGRAM
The SIM program was written for PDF 8/e computers with the
KE8-E extended arithmetic element (EAE). Subroutines were
added for POP 8/e computers without an EAE. Data for evaluation
were acquired with the non-EAE version.
-5-
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1. Data Acquisition
Data acquisition conditions, or parameters, are specified by
teletype communication between analyst and computer (Figure
1). From one to eight m/e values are entered as a set of
masses to be monitored. An integration time (in milli-
seconds) can be specified for each mass, or all masses can
be monitored with the same integration time. The "NO.
POINTS" prompt requests the analyst to specify the number of
times a set of masses is to be monitored before the computer
is to add the acquired data and store the sum.
SYSTEM-150 IS ON SELECT MODE: USER
LOAD FILE: SIMSCN
CALIBRATION FILE: CALI
MASS(ES): 246;248
INTEGRA. TIME:450;45ff
ANOTHER SET7Y
MASS(ES): 235;237
INTEGRA. TIME;450r
ANOTHER SET7Y
MASS(ES): 263
INTEGRA. TIME: 750
NO. POINTS: 5_
RUN TIME: 3ff
TITLE:PESTICIDE MIXTURE
SCALE FACTOR: 8_
DATA FILE NAME: MIX
DATA
Figure 1. SIM program initiation dialogue
After program initiation, integration times and the number
of points can be changed; data acquisition must be halted
only long enough to enter new parameters with appropriate
teletype characters. Three sets of masses, which are
designated during program initiation, may be monitored in
any order with teletype prompts.
2. Data Output
The m/e value first specified to be monitored is plotted as
data are acquired; real-time plot amplitude is controlled by
the scale factor entered via teletype during program initia-
-6-
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tion. After data acquisition is halted, data for all masses
are plotted either overlaid or separately. In either case,
plots are normalized to the most intense signal. Since the
program does not include a background subtraction routine,
the most intense signal may be due to ions from column bleed,
pump oil, or other spectrometer contaminants. The Savitsky-
2
Golay least-squares smoothing routine is used to plot data.
-7-
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SECTION IV
DISCUSSION
The SIM program and standard System/150 specific-mass
detection were compared using data obtained for solutions
containing a mixture of four chlorinated pesticides. After
satisfactory chromatographic conditions were established for
the mixture of four chlorinated pesticides (o_,£!-DDD, p_,p' - .
DDE, £,£'-DDT, and dieldrin), a complete mass spectrum was
obtained for each compound. To determine which masses should
not be used for SIM monitoring, background and column-bleed
spectra were recorded with the same instrumental conditions
that were used for the pesticide spectra.
Both p_,p_'-DDT and o_,p_'-DDD had base peaks at m/e 235 and 67%
fragments at m/e 237. Background ions with these m/e values
were insignificant. The third most intense peak in both
spectra was m/e 165; a significant background contribution
precluded monitoring this ion. Accordingly m/e 235 and 237
were selected for both compounds, which could be distinguished
from each other by GC retention times.
For £,£'-DDE, a unique base peak of m/e 246 along with a
strong m/e 248 (65% of base peak) provided excellent speci-
ficity and sensitivity. The absence of background inter-
ference and the intensity of these peaks made them ideal ions
to monitor.
No ideal ion was found to monitor dieldrin. Background ions
interfered with the base peak at m/e 79 and the three other
strong peaks (m/e 81, 35%; 82, 30%; and 77, 25%). In SIM
trials runs, fluctuations in background ion intensity at these
masses produced "peaks" as strong as those from 1 ng of
dieldrin. Mass 263, although only 5% of base peak intensity,
was used to monitor dieldrin, because background ions at mass
263 were insignificant.
-8-
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After the ions to be monitored were chosen, several runs
were made with the SIM program to determine the best program
parameters. (The relationship between integration times and
number of points affects the apparent GC resolution and peak
sharpness.) Best results were obtained when only masses 235,
246, and 263 were monitored with 250 msec integration time
for each. Five points were added before the sum of intensi-
ties was stored. Data were output as superimposed plots with
each mass plotted separately. (Figure 2). All data points in
a particular data file were normalized with the smallest
stored number set equal to zero and the largest stored number
set equal to 100% relative intensity.
With the spectrometer conditions current when these data
were acquired, 1 uA of the l-ng/u& solution was needed to
observe all four pesticides, but DDT and dieldrin were often
barely discernible. With a l-y£ injection of'the 0.2-ng/yA
solution (Figure 3), DDE (m/e 246) and (m/e 235) were easily
observed, but dieldrin and DDT were not discernible. Moni-
toring only m/e 246 or 235 would increase the apparent
sensitivity. However, no attempt was made to determine a
detection limit for each compound. The limit varies with
instrumental conditions, such as tuning, electron multiplier
condition, spectrometer contamination, quadrupole cleanliness,
separator condition, and electronic stability.
Since data are output only as normalized plots, quantitative
information can be obtained only be comparing relative peak
heights or relative peak areas. To determine SIM peak
reproducibility, six consecutive l-y£ injections of the 1-ng/
A
y£ solution were monitored. All instrumental conditions
were maintained as constant as possible, and the mass
-9-
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PESTICIDE MIXTURE; 1 UL; 1 tG PER UL
235
ODD
263
216
SYSTEM 150 IS ON SELECT MODE: USER-
LOAD FILE: SIMSCN
CALIBRATION FILE: CAL5-
MASSCES): 2351246*263-
INTEGRA. TIME:250
ANOTHER SET?
NO. POINTS: 5
RUN TIME: 25
TITLE: PESTICIDE MIXTURE*
SCALE FACTOR: J6
DATA FILE NAME: MIX I 1
DATA
E
1 ULJ 1 NG PER UL
Figure 2. Plotter output of SIM data obtained from
1 ng each of four pesticides
10
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PESTICIDE MIXTURE; 1 UL; 0-2 N6 PER UL
23S
ODD
263
DDE
216
SYSTEM 150 IS ON SELECT MODE: USER
LOAD FILE: SIMSCN
CALIBRATION FILE: CAL11
MASS(ES): 235)2461263
INTEGRA. TIME: 250
ANOTHER SET?
NO. POINTS: 5
RUN TIME: 25
TITLE: PESTICIDE MIXTURE* 1 ULJ 0.2 NG PER UL-
SCALE FACTOR: 16
DATA FILE NAME: MIXI 4-
DATA
Figure 3. Plotter output of SIM data obtained from
0.2 ng each of four pesticides
11
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spectrometer was mass calibrated before each data acquisition.
From the specific ion chromatograms, peak-area and peak-height
ratios were calculated for each compound relative to o_,p_'-DDD,
which produced the most intense response of the four compounds.
The results (Table 1) showed that peak-height ratios were
more reproducible than peak-area ratios calculated from
planimeter measurements. This result was also reported by
Holland and co-workers. Because of the noise, the greatest
source of error was construction of peak baselines.
Table 1. COEFFICIENTS OF VARIATION FOR SIM DATA
Peak Peak
heights are as a
pfp'-DDT 18% 24%
O,p"-DDD
p,p'-DDE 11% 12%
0,p'-DDD
Dieldrin 8% 8%
o,p'-DDD
Measurements corrected for error in planimeter readings
Data were also collected for four consecutive l-y£ injections
of the 1-ng/yJl pesticide solution with the standard System/
150 data acquisition method. All instrumental conditions
were maintained as constant as possible, and the mass
spectrometer was mass calibrated before each data acquisition.
Masses 235, 246, and 263 were monitored with 1000 msec
integration time for each mass. This integration time was
arrived at experimentally as a compromise. A longer time
theoretically would have increased the apparent sensitivity
but also would have increased the probability of missing a
large portion of some GC peaks. Data were output as total
ion current plots with an overlaid limited-mass ion current
-12-
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plot of each significant ion (Figure 4). Three pesticides,
DDE, ODD, and DDT were readily apparent in the computer-
reconstructed chromatogram, but dieldrin was not detected
in either the reconstructed chromatogram or the m/e 263
limited-mass plot. DDT appeared as a small, broad peak and
would probably not have been apparent with GC retention-
time information.
To compare reproducibility of SIM and System/150 data,
coefficients of variation were calculated for both peak
heights and peak areas (Table 2).
Table 2. COEFFICIENTS OF VARIATION FOR SIM AND
SYSTEM/150 DATA
ODD
DDE
DDT
Dieldrin
Peak
SIM
9%
2%
13%
13%
Heights
System/150
11%
7%
22%
— —
Peak Areas
SIM System/150
12%
15%
8%
12%
17%
8%
7%
— • —
Whereas System/150 requires that masses be monitored in
ascending order, the SIM program permits masses tb be
monitored in any order. System/150 monitoring of masses 235,
237, 246, and 248 for a mixture of ODD, DDE, and DDT is
hampered by the ascending mass order requirement. With the
relatively long integration times required, too much time
would be spent on masses 235 and 237 (indicative of ODD and
DDT) while the DDE peak (masses 246 and 248) eluted. Likewise,
much of a sharp ODD peak could elute and be missed while
masses 235'and 237 were monitored. The SIM program permits
alternating the masses indicative of DDE with masses indicative
of DDD and DDT, and masses can be monitored in the order:
235, 246, 237, and 248.
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PESTICIDE MIXTURE; 1 U_; 1 NG PER U-
8
«"^«
SL
8_
2
8.
V ^
k
8.
o
B
C
DDE
A — m/e 263
B - m/e 235,246, and 263
C - m/e 235
D - m/e 246
0 10 20 30 10 SO 60 70 80 90 100 110 120 130 110 ISO 160 170 180 130 200 210 220 230
SPECTRUM NUMBER
Figure 4. System/150 data obtained from a solution containing 1 ng each of
four pesticides
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The SIM program permits data acquisition parameters to be
changed with minimal interruption of data acquisition and
without initiating a new data file, which is required with
System/150. Increased sensitivity was obtained by using
the SIM program's three sets of masses to devote all scan
time to the mass of interest for each GC peak (Figure 5).
During program intiation, the appropriate mass was designated
for each set. The first set, m/e 246, was monitored until
the first peak (DDE) eluted. The second set, m/e 263, was
monitored until the second peak (dieldrin) was observed, and
the third set, m/e 235, was monitored for DDD and DDT, the
third and fourth peaks, respectively. For each set change,
data acquisition was halted only long enough to enter two
characters via teletype.
A significant disadvantage of the SIM program is the inability
to eliminate background data. SIM data plots are normalized
to the most intense signal, which might be composed mainly of
background signals with only a small contribution from sample.
Since System/150 data are stored as discrete spectra, back-
ground data can be subtracted and the appropriate spectrum
plotted to show relative intensities of monitored ions. For
example, both m/e 235 and 237 must be present to confirm the
presence of DDT, and their relative intensities are significant
information. An approximation of sample concentration can be
obtained with System/150 data by comparison of the absolute
number of counts for the sample peaks (after background sub-
traction) with those for a standard analyzed with the same
conditions. However, since SIM data are output as normalized
plots, concentration estimates require internal standards.
The SIM program version used to collect these data contained
some annoying bugs. An operator typographical error during
program parameter changes (such as typing a character not
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PESTICIDE MIXTURE; 1 UL; 1 NB PER U_
DDE
DDD
m/e 235
m/e 263
SYSTEM 15USER
LOAD FILE: SIMSCN
CALIBRATION FILE: CAL7
MASSCES): 246
INTEGRA. TIME:500
ANOTHER SET?Y
MASSCES): 263
INTEGRA. TIME:500
ANOTHER SET7Y
MASSCES): 235
INTEGRA. TIME:500
NO. POINTS: 5
RUN TIME: 30
TITLE»PESTICI BE MIXTURE*
SCALE FACTOR: 10
DATA FILE NAME: MIX8
DATA
S2
S3
J UL; 1 NG PER UL-
m/e 246
Figure 5. SIM data obtained from 1 ng each of four
pesticides when three mass sets were used
16
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recognized as a parameter designator) halted data acquisition
without the proper termination sequence. The data file was
therefore inaccessible. Manual termination of data acquisition
had to be done cautiously. When the teletype did not echo
the termination character "E" before the carriage return
was activated, the data file was not terminated properly and
was therefore inaccessible.
Interferences with SIM data acquisition were observed after
a Tektronix 4012 cathode ray tube (CRT) was integrated into
the GC-MS-Computer system. Local-mode graphics CRT operation
produced major plotter pen displacements on both real-time
and final output. No evidence was found that local-mode CRT
operation interfered with System/150 data acquisition.
-17-
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SECTION V
REFERENCES
1. Neher, M. B., and J. R. Hoy land. Specific-Ion Mass
Spectrometric Detection for Gas Chromatographic Pesticide
Analysis. Battelle Columbus Laboratories, Columbus, Ohio.
Environmental Protection Agency Publication Number EPA-
660/2-74-004. January 1974.
2. Savitsky, A., and M. J. E. Golay. Smoothing and Differen-
tiation of Data by Simplified Least Squares Procedure.
Anal. Chem. 8: 1627-1638, 1964.
3. Holland, J. F. , C. C. Sweeley, R. E. Thrush, R. E. Teets,
and M. A. Bieber. On-Line Computer Controlled Multiple
Ion Detection in Combined Gas Chromatography-Mass Speq-
trometry. Anal. Chem. 45: 308-314, February 1973.
-18-
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SECTION VI
APPENDIX
SIM Program Dialogue
MASS(ES): From one to eight masses are designated; the
first mass specified is displayed on the plotter during data
acquisition.
INTEGRATION TIME: Response specifies the time (1 to 4096
milliseconds) each mass is to be monitored. Integration
times are paired with masses previously entered; the first
integration time is used for the first mass designated etc.
When more masses than integration times are entered, the
last time is used for masses that have no corresponding time.
If all masses are to be scanned for the same period, only
one time value must be entered.
ANOTHER SET?: A positive response allows up to eight masses
to be entered to form a new mass set (maximum of three sets).
NUMBER OF POINTS: Response specifies how many times the mass
set is scanned before values for each mass are summed and
stored.
RUN TIME: After number of minutes specified, data acquisition
will be automatically halted.
SCALE FACTOR: Amplification factor controls real-time plot
amplitude.
The SIM Program permits some parameters to be changed with
operator-computer communication via teletype during data
acquisition. Permissible parameter designators are
E - terminates data acquisition before expiration of time
entered during program initiation
F - followed by number - changes real-time amplification
factor
N - followed by number - changes the number of times each
mass is scanned before values are summed and stored
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S - followed by number 1, 2, or 3 - begins data acquisition
for a different mass set which was entered during program
initiation
T - followed by number(s) - changes integration time for
the masses being monitored to the time (milliseconds)
specified with new number
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SELECTED WATER
RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
1. Re port No.
2.
3. Accession No.
w
4. Title
EVALUATION OF A COMPUTER PROGRAM FOR GC-MS
SPECIFIC ION MONITORING,
7. AuthoT(s)
Alford, A. L.
5. RepoitDate
S. Performing Organization
Report $0,
10. Project No.
9. Organization
Analytical Chemistry Branch, Southeast
Environmental Research Laboratory
11. Contract/Grant No.
1). Type uf'RepQi t and
Period Covered
12. Sponsoring Organ!Button Environmental Protection Agency
15. Supplementary Notes
Environmental Protection Agency report number,
EPA-660/2-74-002, June 1971*
16. Abstract
A computer program, "Specific-Ion Mass Spectrometric Detection for
Gas Chromatographic Pesticide Analysis" (SIM), developed under an
Environmental Protection Agency (EPA) grant, was evaluated at the
EPA1s Southeast Environmental Research Laboratory. Standard
solutions of four chlorinated pesticides were used to compare the
SIM program data to those produced by an existing limited-mass data
acquisition program. Under similar conditions, similar sensitivities
were observed with both programs. Greater sensitivity was obtained
with the SIM program when its parameter selection options were
fully utilized.
i7a. Descriptors * Analytical techniques, * Mass spectrometry, * Gas
chromatography, * Computer programs, Chlorinated hydrocarbon
pesticides
lib. identifiers * Computer-controlled GC-MS, * Specific-ion monitoring,
* Multiple-ion detection, * Mass fragmentography
I7c. CO WRR Field & Group Q5A
18. Availability
19. Security C/ass;
fReporf)
30. Severity CL'Ss.
CPafe-)
21, No, of
Page's\,
?2. jR/ies?
Send To:
WATER RESOURCES SCIENTIFIC INFORMATION CENTER
U.S. DEPARTMENT OF THE INTERIOR
WASHINGTON. D. C. 2O24O
Abstractor
. L. Alford
I institution Southeast Environmental Research Lab
WBSIC 1O2 (REV. JUNE 1971)
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