Environmental Monitoring Series
TECHNIQUES FOR OPTIMIZING A
QUADRUPOLE GC/MS/COMPUTER SYSTEM
Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Athens, Georgia 30601
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. 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 are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the 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 as a function of time or meteorological factors.
This document is available to the public through the National Technical Informa-
tion Service. Springfield, Virginia 22161.
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EPA-600/4-76-004
March 1976
TECHNIQUES FOR OPTIMIZING A QUADRUPOLE
GC/MS/COMPUTER SYSTEM
by
Mike H. Carter
Analytical Chemistry Branch
Environmental Research Laboratory
Athens, Georgia 30601
U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE-OF RESEARCH AND DEVELOPMENT
ENVIRONMENTAL RESEARCH LABORATORY
ATHENS, GEORGIA 30601
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DISCLAIMER
This report has been reviewed by the Athens Environmental
Research 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.
11
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ABSTRACT
Techniques and procedures have been developed for
maintaining the stability and maximizing the sensitivity of
the Finnigan 1015-System 150 Gas Chromatograph/Mass
Spectrometer/Computer (GC/MS/Computer) System. Causes of
instability include poor vacuum tube performance and high
temperature in the electronics chassis. Sensitivity is
maximized by appropriate maintainance and adjustment
techniques.
Methods have been developed for increasing the utility of
the data collected by the GC/MS/Computer system. These
include techniques for acquiring better data and for
extracting the most information from the data that have been
acquired.
This report was submitted in partial fulfillment _of ROAP
16ADN Task 27 at the Environmental Research Laboratory,
Athens, Georgia. Work was completed as of April 1974.
111
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CONTENTS
Sections Page
I Conclusions and Recommendations 1
II Introduction 2
III Experimental 3
IV Results and Discussion 4
V References 22
VI Glossary 23
VII Appendices 24 & 26
v
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FIGURES
No. Page
1 Spectrum of Methyl Linoleate Showing
Incorrect Mass Assignment At m/e 295 5
2 Reconstructed Gas Chromatogram of
Decafluorotriphenylphosphine With
FC-43 Reference at End of Run 9
3 a Decafluorotriphenylphosphine Spectrum
From Leading Edge of RGC Peak 10
b Decafluorotriphenylphosphine Spectrum
From Trailing Edge of RGC Peak 10
4 Spectrum of Nonachlor Obtained Using
2 ms Integration Time Below Mass 250 and
17 ms Integration Time Above Mass 250 12
5 Reconstructed Gas Chromatograin of Paper
Mill Effluent 15
6 Superimposed Mass 59 and Mass 95 Limited
Mass Range Reconstructed Gas Chromatograms
of Paper Mill Effluent 16
7 Spectrum 124 Minus 123 of Paper Mill
Effluent (Borneol) 17
8 Spectrum 130 Minus 124 multiplied by 0.5 of Paper
Mill Effluent (Alpha-Terpineol) 18
9 Computer Matches of Spectra in Figures
7 and 8 19
10 a Reconstructed Gas Chromatograin of Paper
Mill Effluent (Methyl Esters) 20
b Superimposed Mass 74 and Mass 87 Limited
Mass Range Reconstructed Gas Chromatograms
of Paper Mill Effluent (Methyl Esters) 21
11 a Baseline Resolution Between Masses
69 and 70 25
b 50% Valley Resolution Between Masses
219 and 220 25
c 90% Valley Resolution Between Masses 502 and
503 25
vi
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SECTION I
CONCLUSIONS AND RECOMMENDATIONS
Appropriate operator techniques are essential in maintaining
the sensitivity and stability of the Finnigan 1015
GC/MS/Computer system. The utility of the data acquired can
be improved significantly by operator action.
The techniques discussed herein have been found to be
effective on our system. Other users of this type
instrumentation should employ these techniques when
necessary.
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SECTION II
INTRODUCTION
The most powerful tool currently in use for the analysis of
organic pollutants is computerized Gas Chromatography/Mass
Spectrometry. Since this instrumentation represents a
sizable investment, it should be available for use as much
of the time as possible and the performance of the system
should be maintained at the highest possible level.
The Environmental Research Laboratory received the first
quadrupole GC/MS/Computer system in the EPA four years ago.
The maintenance techniques described in this report were
compiled from experience gained during the past four years
in the analysis of various types of organic pollutants (1,
2). When used in conjunction with the instrument
instruction manual (3) and the software manual (4), these
techniques have been effective in maintaining instrument
stability and sensitivity.
Also, techniques were developed to simplify the
interpretation of data. These include methods for acquiring
better data and for extracting the maximum useful
information from the data after it has been acquired.
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SECTION III
EXPERIMENTAL
Gas chromatograph/mass spectrometer -- Results described
were obtained using a Finnigan 1015-C quadrupole mass
spectrometer interfaced to a modified Varian 1400 gas
chromatograph by means of a glass jet separator.
Data system — The data system was a System 150 supplied by
System Industries and based on a Digital Equipment
Corporation PDP-8e computer with 4K of core storage. I/O
devices included a teletype, magnetic tape and magnetic disk
data storage, x-y plotter, and mass spectrometer interface.
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SECTION IV
RESULTS AND DISCUSSION
MAINTAINING MASS SPECTROMETER STABILITY
Instability in the mass spectrometer may cause drift that
can invalidate the mass number calibration file used by the
data system, leading to incorrect assignment of mass
numbers. Interpretation of the resulting data is
impossible. For example, in Figure 1, a spectrum of methyl
linoleate, the molecular ion is shown at m/e 295 instead of
at the correct value of 294. The calibration file used had
been verified prior to data collection by obtaining spectra
of the calibration standard and checking the accuracy of
mass number assignment. In another case, a shift of less
than one mass number was observed when a calibration with
perfluorotributylamine (FC-43) was verified. The relative
intensities of the mass 502 and 503 ions of the FC-43
spectrum were approximately equal instead of in the correct
10:1 ratio.
Checking for Drift
If the operator suspects that drift is occurring during a GC
run, a check may be performed by taking several reference
spectra at the end of the run. Just prior to the
termination of data collection, FC-43 or any suitable
standard may be introduced through the batch inlet system.
The amount introduced should not produce a total ion current
large enough to be the base spectrum in the RGC and it
should not saturate the integrator. The standard spectra
provide a simple means of checking for correct mass number
assignment (Figure 2). Possible causes for this type of
instability include heat, vacuum tube failure, and low
temperature of the ionizer.
Heat
A common cause of instability is excess heat in the
electronics of the mass spectrometer, particularly in the
radio frequency generator chassis. This excess heat is
usually caused by a dirty air filter or cooling fan failure.
In an unusual case reported by Dr. D. Craig Shew of the
Robert S. Kerr Environmental Research Laboratory, a change
in component location by the manufacturer caused a power
transformer to receive less cooling that it had received
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MOW. UNQLSRTC
m.
s_
_M
50 SB 70 90 30 100 110 J20
...... .,,...,...., ......... j....,...^,^.,,.^ ...... ..,, ......... , ........ r..|,.
1SB 168 17B 180 130 2BB 210 220 23B 2« Z9i
399 270 280 290 380 310 33J 330 310 39f
M/ E
Figure 1. Spectrum of Methyl Linoleate Showing Incorrect Mass Assignment At
m/e 295
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previously. The resulting instability was corrected by
boring holes in a chassis partition to increase air
circulation to the transformer.
Vacuum Tube Failure
Drift is frequently caused by decline in vacuum tube
performance. The three 807 tubes and the 6AL5 tube in the
RF generator fail most frequently and may have to be
replaced every six months. Instability in the reconstructed
gas chromatogram (RGC) of FC-43 from the batch inlet system
is an indication of tube failure.
Tube performance may be tested by introducing sufficient FC-
43 (approximately 1 Ul) to give an operating pressure of
about 2x10~6 Torr with the separator blanked off.
Integration times of 4 ms from mass 30 to mass 250 and 17 ms
from mass 251 to mass 620 should be selected. In normal
operation the amplitude of the total ion current for
successive spectra varies by less than 5 percent. If the
tubes are defective, the deviation in amplitude may be as
much as 40 percent. After the tubes have been replaced and
allowed to stabilize for at least an hour, the DC Zero and
Balance procedure and the DC/RF Generator adjustment must be
performed as described in the 1015 Instruction Manual.
Warmup Time
After the ionizer has been on for about fifteen minutes, a
discrete shift in calibration may occur. According to
Finnigan personnel, the shift may be caused by a change in
quadrupole rod geometry induced by heat from the filament of
the ionizer. The problem can be eliminated by turning the
ionizer on for at least fifteen minutes prior to obtaining a
calibration file on the data system. This is necessary
mainly for GC runs longer than fifteen minutes.
MAXIMIZING SENSITIVITY
Lack of sensitivity in the mass spectrometer leads to higher
noise levels because increased signal amplification is
required. Furthermore, because of low sensitivity the need
for large amounts of sample may preclude analysis of
materials present at very low concentrations. It is
therefore important to have maximum sensitivity available at
all times.
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Resolution adjustment must be performed daily to maximize
mass spectrometer sensitivity. Appendix I outlines the
adjustment procedure used regularly in our laboratory.
Periodic maintainance is also important in maintaining mass
spectrometer sensitivity. We use a modified version of the
Finnigan procedures in the Instruction Manual for the 1015-C
for cleaning the quadrupole rods and the electron
multiplier.
Quadrupole Rod Cleaning
The procedure recommended in the Finnigan manual was found
to be insufficient when, following an instrument shutdown, a
rapid loss of sensitivity and a drastic decline in peak
shape quality was noted after the ionizer was turned on.
The erratic behavior was found to be caused by a film on the
rods, which was not removed by the suggested cleaning
procedure. Therefore, a procedure was developed to remove
the deposit. After removing the black dielectric deposits
from near the ends of the rods by rubbing with an alumina-
methanol slurry and a cotton-tipped swab, the rods were
cleaned with successive washes of ethyl acetate, acetone,
and methanol. This multi-solvent washing was found to be
more effective for the removal of organic films than a rinse
with methanol alone.
Electron Multiplier Regeneration
A similar film on the electron multiplier inhibited
regeneration. The multiplier was cleaned with successive
washes of the three solvents mentioned previously, and it
was baked in air for one hour at 340°c. After baking, the
multiplier was reinstalled and placed under vacuum as
quickly as possible to prevent degeneration by atmospheric
water vapor. This procedure resulted in a five-fold
increase in sensitivity. The multiplier has been
regenerated eight times with no overall decline in
performance.
Separator Clogging
The separator also has a significant effect on the
sensitivity of the GC/MS system. If the separator is
partially clogged or the carrier gas flow is adjusted
improperly, sensitivity is markedly reduced. A partially
clogged separator is indicated when solvent peaks tail
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excessively or the operating pressure of the system
approaches the pressure of the system with the separator
sealed off. If a clogged separator is suspected, the jets
should be inspected for foreign matter with a small
magnifying glass.
A minimum carrier gas flow of 14-16 ml per minute is
required for satisfactory separator operation. Optimum
efficiency may occur at an even higher flow rate, which can
be used if GC resolution is not critical. Separator effects
will be further discussed in the next section.
Solid Probe
A very simple method for increasing GC/MS sensitivity is the
insertion of the solid sample probe into the ionizer, A
clean sample container should be in place at the tip of the
probe. Insertion of the probe results in a more tightly
enclosed ionizing volume, which in turn provides a higher
concentration of sample molecules for ionization (5). The
temperature of the probe should be adjusted to approximately
that of the instrument manifold.
SIMPLIFYING INTERPRETATION
One problem in the interpretation of GC/MS data is in the
comparison of guadrupole with magnetic deflection mass
spectra. Low mass ion intensities are enhanced by the
quadrupole system, causing the relative intensities of high
mass ions to be lower than those obtained on magnetic
instruments. The tune-up procedure outlined in Appendix I
is one technique to enhance high mass ion intensity.
Another way to achieve this enhancement is to make a
judicious choice of spectra for output. By choosing a
spectrum from the leading edge of the RGC peak, high mass
relative ion intensity can be increased. On the leading
edge of the RGC peak sample concentration is increasing
during the scan and, since the 1015-C scans from low to high
mass, more sample is in the ionizer during the high mass
portion of the scan.
Figure 2 shows the RGC of a decafluorotriphenylphosphine
sample supplied by the Analytical Quality Control Laboratory
(AQCL), Cincinnati. Figure 3a is a spectrum from the
leading edge of the RGC peak and Figure 3b is a spectrum
from the trailing edge of the peak. The higher intensity of
the M+ ion at mass U42 is evident in Figure 3a. This effect
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flQCL CHECK SFHtE
T ' ' I"••>••• !'
10 29 33 <
gPECTRLh NL*6ER
SB 66
i '
70
80 90
100 110 133
Figure 2. Reconstructed Gas Chromatogram of Decafluoro-
triphenylphosphine With FC-43 Reference at End
of Run
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e
s_
SPECTFU1 MretJI 83
RCCL OCX SFWLE
I
20 33 K3 S3
M/ E
70 93 33 'll53 'ilO \3S 133 1*3 133 160 170 1S3 190 330 Z10 220 Z30 ?«3 293 283 270 280 230 300 310 325 335 318 393 360 370 380 333 «0 110 12B 133 ttO 1SO 168 m3 180
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will be most pronounced when scan times are long with
respect to GC elation times.
Correlating Gas Chromatoqrams
Another problem encountered was a difficulty in correlating
GC/MS RGC's with gas chromatograph runs made on the same 50'
SCOT column in an off-line GC operated with a flame
ionization detector at atmospheric pressure. The column
appeared to have greater efficiency when it was connected in
the GC/MS. This problem was solved by adjusting the carrier
gas flow of the off-line GC to approximately one half the
flow through the GC/MS. The flow rate through the GC/MS was
measured before the column was connected to the separator
and was checked after connection by measuring the exhaust
from the separator vacuum pump.
The higher efficiency on the GC/MS column may result from a
higher pressure at the column outlet caused by the
constriction in the jet separator. The inlet pressure was
the same in both instances. According to McNair and Bonelli
(6), column efficiency is increased as the ratio of inlet to
outlet pressure approaches unity.
Optimum Integration Time
A technique for obtaining good spectra from low sample
concentrations is the use of the longest integration times
that are practical from the standpoint of peak elution times
and integrator saturation. In the System 150 software, the
analog to digital converter (ADC) value for each mass is
normalized to 1 ms integration time by dividing it by the
integration time for that mass. Normalization of the small
ADC values obtained with short integration times and small
amounts of sample, however, results in many masses having
the same amplitude, as illustrated in Figure 4 from mass 33
to 250.
Figure 4 is the mass spectrum of a compound found in the
effluent of a pesticide manufacturing plant and tentatively
identified as nonachlor. The integration time from mass 33
to 250 was set at 2 ms because of some large GC peaks in the
sample. The integration time from mass 251 to 450 was 17
ms. The data above mass 250 show better statistical quality
because of the longer integration time.
We usually try to compensate for the lower sensitivity of
the quadrupole at high mass by using longer integration
11
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NONRCH_OR
tr —
2B 30 SO 50 60 70 80 30 100 110 120 130 1W 133 160 170 180 130 200 210 22D 230 210 2SO 2KB Z7B 280 230 3BB 310 32B 330 3tO 3SO 360 370 3H3 330 WO 110 VS 130 'HB 1SO 163 170
Figure 4. Spectrum of Nonachlor Obtained Using 2 ms Integration Time Below Mass
250 and 17 ms Integration Time Above Mass 250
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times for masses above 250. A typical choice of integration
times and mass ranges in the high mass range is 4 ms from
mass 33 to 250 and 17 ms above mass 250.
The signal optimization mode of data collection or IFSS
(Integration time as a Function of Signal Strength) can give
better data on small RGC peaks while not saturating on large
peaks. However, since the instrument integrates longer on
small peaks than large ones, some spectra take longer than
others and the Spectrum Number scale of the RGC is not
linear with respect to time. The RGC will therefore be
distorted when compared to a GC run. The IFSS mode has been
found to use more disc or tape storage than the normal, or
CONTROL, mode.
Superimposed LMRGC's
The utility of limited mass range reconstructed gas
chromatograms (LMRGC1s) can be increased by superimposing
LMRGC's on RGC's or other LMRGC's. One application of this
technique is in the analysis of unresolved GC peaks, as
illustrated in Figure 5, the RGC of a paper mill effluent.
The major GC peak at spectrum number 127 appears to be due
to a single component. However, two terpenes likely to be
in this sample were known to have practically identical
retention times on the column being used. The terpenes were
alpha-terpineol, which has a base peak at mass 59, and
borneol, which has a base peaK at mass 95. Therefore two
LMRGC1s, one for mass 59 and one for mass 95 were
superimposed, as shown in Figure 6.
Based on the information obtained from the superimposed
LMRGC's, two background-subtracted spectra were plotted.
The plot of spectrum 124-123 is shown in Figure 7 and
spectrum 130 minus spectrum 124 multiplied by an
amplification factor of 0.5 is shown in Figure 8. These two
spectra indicated that both components were present in the
sample. The result of matching these spectra on the
Battelle/Biemann matching program is shown in Figure 9. A.
similarity index (SI) of 1.00 is a perfect match.
Superimposed LMRGC1s can also be used to indicate classes of
compounds. Figure lOa is the RGC of a methylated paper mill
effluent sample. The two main peaks in the mass spectra of
methyl esters of saturated fatty acids are at masses 74 and
87- Methyl esters of fatty acids are indicated by
simultaneous peaks on both LMRGC1s, such as at spectrum
number 255 of Figure 10b. Mass spectrum 255 was that of
methyl palmitate.
13
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Appendix II gives a procedure for superimposing RGC's and
LMRGC's. This procedure, furnished by Mr. J. G. Watt of
System Industries, eliminates redrawing the axes of the
graph with each successive plot.
14
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IftH WU. SFFUJENT
8.
8.
8.
R-
0
n
i^ h ft
V___ /JWJW^/vJ
L ,. ^v . A . . „ __ r
3 10 3S 3} m 93 83 TO 80 33 100 IIS 135 138 I« 193 183 178 168 130 200 210 233 330 2-te 2SO 2EO 270 3BO 290 3BO 310 33! -i30 3M 333 360 370 380 390 MO 418 '120 -OO -HO «3 160 TTB -SO
3-tcTMLH MJ-631
Figure 5. Reconstructed Gas Chromatogram of Paper Mill Effluent
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IWER rtJU. ffFLUEKI
P-
8_
R.
18 ZB 30 16 SB
SPECTRM MJKB
95 38 188 118 128 130 1W 190 183 ITU 190 130 ZOO ZIO ZZ8 230 2*3 2Sfl ZBO 270 298 238 300 310 320 'JX 3W 3S8 368 378 390 330 «B «8 «0 13B tM «B Kg 178 188
Figure 6. Superimposed Mass 59 and Mass 95 Limited Mass Range Reconstructed Gas
Chromatograms of Paper Mill Effluent
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SPECTFLM UJKfl 121 - 1Z3
B WER mu. arum
f-9
l%-
R
-W
^
23 30 1
n/ e
SB S3 70 80 30 I8B HO iZO ISO 110 ISO 168 178 180 130 TSS 210 228 230 ZV3 ZSO
770 290 23B 380 318 328 330 310 3SO 368 370 388 338 «B
-------
SPECTHUM HJhKR 133 - 121
fWBB HIUL QTUUEWT
SsR_
r-B
20 3d 18 S3 63 78 38 33 IflO I IB 120 138 110 ISO 188 17B 198 138 208 218 ZZB 238 210
268 278 280 238 308 318 328 338 310 3SO 360 378 3B8 338 108 118 «8 138 110 1S8
Figure 8. Spectrum 130 Minus 124 multiplied by 0.5 of Paper Mill Effluent
(Alpha-Terpineol)
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S, E, P, R, OR C? S
I.D.? PAPER MILL SAMPLE
PAPER TAPE7N
FN—I1T124; SP--1
PAPER MILL EFFLUENT
PARMTRS? M90-200
45 HITS
BORNEOL (SEWL)tL55 ATJ A A B CGt 154 C10.H18.0 BSR 0212
FILE KEY= 8697
SI=0.811
ISOBORNEOL (SEWL)tL55 ATJ A A B COt 154 C10.H18.0 BSR 0215
FILE KEY= 8700
SI=0.706
2,5- DIMETHYL 2,4-HEXADIENE 110 C8.H14 AST 0020
FILE KEY= 17
SI=0.392
ISO-BORNEOL 154 C10.H18.0 MSC 1711
FILE KEY= 6296
SI=0.363
2,3-DIMETHYLHEXA-l,4-DIENE 110 C8.H14 MSC 3265
FILE KEY= 7807
SI=0.351
S, E, P, R, OR C?S
I.D.? PAPER MILL SAMPLE
PAPER TAPE7N
FN--I1T130;SN—1; :
PAPER MILL EFFLUENT
PARMTRS? M100-350
59 HITS
ALPHA-TERPINE0L 154 C10.H18.0 MSC 1720
FILE KEY= 6305
SI=0.717
2-TERPINE0L 154 C10.H18.0 AST 1671
FILE KEY= 1133
SI=0.682
MYRCEN0L (SEWL) 152 C10.H16.0 BSR 0210
FILE KEY= 8695
SI=0.540
Figure 9. Computer Matches of Spectra in Figures 7 and 8
19
-------
8.
ft.
S.
19 £9 W * GB W T6 iB 88 1« 119
otrmn KWH
1*5 IGD iw
Figure lOa. Reconstructed Gas Chromatogram of Paper Mill Effluent (Methyl Esters)
-------
Figure lOb.
Superimposed Mass 74 and Mass 87 Limited Mass Range Reconstructed
GasChromatograms of Paper Mill Effluent [Methyl Esters)
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SECTION V
REFERENCES
1. McGuire, J. M., A« L. Alford, and M. H. Carter.
Organic Pollutant Identification Utilizing Mass
Spectrometry. Environmental Protection Agency, Athens,
Georgia. Publication Number EPA-R2-73-234. July,
1973. p. 15-28.
2. Alford, A. L. Environmental Applications of Advanced
Instrumental Analyses: Assistance Projects, FY72.
Environmental Protection Agency,, Athens, Georgia.
Publication Number EPA-660/2-73-013. September, 1973.
p. 6-31.
3. Instruction Manual - 1015C Series Mass Spectrometers
and GC/MS System^ Finnigan Corporation, Sunnyvale,
California, 1971.
4. System/150 Operations/Reference Manual. System
Industries, Sunnyvale, California, 1972.
5. McFadden, W. H, Tecjhniques in Combined Gas
Chromatogjraphy/Mass Spectrometry Lecture Notes. W. H.
McFadden, 1972. p. 11-13.
6. McNair,, H. M. and E. J. Bone Hi. Basic Gas
Chromatography. Varian Aerograph, Walnut Creek,
California, 1969. p. 30.
22
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SECTION VI
GLOSSARY
FC-43 -- perfluorotributylamine^. a calibration standard
material.
GC -- gas chromatography, a separation technique based on
the partition of materials between gas and liquid
phases.
GC/MS -- a union of GC and MS in which the chromatograph
effluent passes precludes a separator into a mass
spectrometer inlet.
LMRGC -- limited mass reconstructed gas chromatogramy a
computer output that shows the relative currents
resulting from positive ions of particular mass-to-
charge ratio reaching the mass spectrometer detector as
a function of scan number.
M+ -- the ionized molecule, produced by the removal of one
electron with no accompanying fragmentation of the ion.
MS -- mass spectrometry, an identification technique based
on the fragmentation of ionized materials.
RGC -- reconstructed gas chromatogram^ a computer output
that shows the relative currents resulting from summing
all positive ions reaching the mass spectrometer
detector as a function of scan number. This plot
usually resembles the chromatogram obtained in GC.
23
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APPENDIX I
Resolution Adjustment Procedure
We use the following procedure to adjust the high mass range
resolution on our Finnigan 1015-C. This is a modification
of the procedure outlined on pp 6-15 through 6-19 of the
1971 1015-C manual.
The data system should be in the MANUAL mode of operation so
that spectra are displayed on the oscilloscope. Sufficient
FC-43 should be introduced through the batch inlet to give
an amplitude at mass 502 of at least 3 cm at a scope
sensitivity of 20 mV/cm.
The ion energy is set to 5V. The peak at mass 264 should be
maximized by adjusting the extractor voltage and the lens
voltage. Next, resolution between masses 69 and 70 is
adjusted to baseline resolution (Figure lla) with trimpot R-
81 on circuit board PC.5. Resolution between masses 219 and
220 is then adjusted to a valley of approximately 50% of
mass 220 amplitude (Figure lib) with trimpot R-77. Since
the adjustments of R-81 and R-77 interact, the two
adjustments sh'ould be repeated until the desired resolution
at both points is achieved. After accomplishing this, the
resolution between masses 502 and 503 is adjusted to a
valley of approximately 90% of mass 503 amplitude with
trimpot R-180 (Figure lie).
The high mass range of the 1015-C has a secondary amplifier
circuit to enhance high mass intensity. The lower mass
threshold of this circuit is set by the following procedure.
The same oscilloscope display of the FC-43 spectrum as
mentioned previously is used.
The first and last mass controls are set so that the mass
219 peak is at the left side and the mass 264 peak is at the
right side of the oscilloscope display. Then, the amplifier
gain of the circuit is set to maximum by turning trimpot R-
180 fully counterclockwise. Next, trimpot R-179 is adjusted
to give a baseline rise approximately one cm to the left of
mass 264. Finally, R-180 should be readjusted to give the
desired resolution between masses 502 and 503.
24
-------
ro
ui
b
Figure 11
a. Baseline Resolution Between Masses 69 and 70
b, 50% Valley Resolution Between Masses 219 and 220
c. 90% Valley Resolution Between Masses 502 and 503
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APPENDIX II
Procedure for Superimposing LMRGC's
The procedure to bypass the construction of axes by the
plotter involves halting the computer, making 3 changes in
the memory of the PDP-8, and restarting the computer. The
first step is to plot the first RGC or LMRGC, including
axes. Then, enter the output parameters for the LMRGC to be
superimposed on the original. After responding to the final
prompt, "EXPAND BY:", wait until the plotter begins to move
and stop the computer with the "HALT" switch.
At this point, manually relocate the pen position to the
origin of the axes. This should be done with care so that
the spectrum mumbers of the traces will correspond. A
different color pen, which further simplifies
interpretation, can be inserted at this point. The
following changes then must be toggled into the memory of
the PDP-8 by means of the switch register. All numbers are
octal.
Location Old Instruction New Instruction
2007 4731 7000 (NOP)
2010 4732 7000 (NOP)
2013 1737 5271 (JMP Begin
Trace)
Finally, the starting address of 1777 is loaded into the
switch register and the "LOAD ADDRESS", "CLEAR", and
"CONTINUE" key are pressed. After a brief (in the case of
the disk system) pause the plotter will superimpose the
LMRGC on the original axes.
26
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing]
1. REPORT NO.
EPA-600/4-76-004
2.
4. TITLE AND SUBTITLE
Techniques for Optimizing a Quadrupole
GC /MS /Computer System
7. AUTHOR(S)
Mike H. Carter
9. PERFORMING ORGANIZATION NAME AN
Environmental Research
Office of Research and
U.S. Environmental Pro
Athens, Georgia 30601
D ADDRESS
Laboratory
Development
tection Agency
12. SPONSORING AGENCY NAME AND ADDRESS
Same as above
3. RECIPIENT'S ACCESSION-NO.
5. REPORT DATE
March 1976 (Issuing Date),
6. PERFORMING ORGANIZATION CODE
8. PERFORMING ORGANIZATION REPORT NO.
10. PROGRAM ELEMENT NO.
1BA027; RDAP 16ADN; Task 27
11. CONTRACT/GRANT NO.
13. TYPE OF REPORT AND PERIOD COVERED
In-house
14. SPONSORING AGENCY CODE
EPA-ORD
15. SUPPLEMENTARY NOTES
16. ABSTRACT
Techniques and procedures have been developed for maintaining the
stability and maximizing the sensitivity of the Finnigan 1015-System
150 Gas Chromatograph/Mass Spectrometer/Computer (GC/MS/Computer)
System. Causes of instability include poor vacuum tube performance
and high temperature in the electronics chassis. Sensitivity is
maximized by appropriate maintainance and adjustment techniques.
Methods have been developed for increasing the utility of the data
collected by the GC/MS/Computer system. These include techniques
for acquiring better data and for extracting the most information
from the data that have been acquired.
This report was submitted in partial fulfillment of ROAP 16ADN Task
27 at the Environmental Research Laboratory, Athens, Georgia. Work
was completed as of April 1974.
17.
a. DESCRIPTORS
KEY WORDS AND DOCUMENT ANALYSIS
b. IDENTIFIERS/OPEN ENDED TERMS
*Mass spectrometry, *Gas chromato- *GC/MS, Computer
graphy, Computers, Instrumentation controlled, Quadru-
pole, Analytical
techniques
13. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
EPA Form 2220-1 (9-73)
19. SECURITY CLASS (This Report)
UNCLASSIFIED
20. SECURITY CLASS (This page)
UNCLASSIFIED
c. COSATI Field/Group
05A
21. NO. OF PAGES
33
22. PRICE
27
£U.S. GOVERNMENT PRINTING OFFICE: 1976-657-695/5385 Region No. 5- II
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