Gas Chromatograph/ Mass Spectrometer Techniques for Determination of Interferences in Pesticide Analysis Ernest J. Bonelli Finnigan Corporution, 595 N . Pastoria, Sunnycale, Calif, 94086 THEELECTRON C A P T U R E DETECTOR has long been employed in the analysis of chlorinated hydrocarbon pesticides. Its high sensitivity and excellent selectivity have made it the detector of choice in pesticide analysis. Some of the recent chemicals found in the environment are the polychlorinated biphenyls (PCB's). These industrial compounds are structurally similar t o the chlorinated hydrocarbon pesticides and thus may interfere with qualitative and quantitative electron capture analysis ofthe pesticides. PCB's and chlorinated naphthalenes have been separated by silicic acid column chromatography prior t o analysis by gas chromatography ( I , 2 ) . However, the use of a gas chromatographimass spectrometer enables the qualitative and quantitative analysis of these compounds without prior column chromatography or complete separation on a gas chromatographic column. Goerlitz and Law (3)have recently analyzed chlorinated naphthalenes by GC/MS; however, they were not analyzed in combination with interfering substances.
C-URINFIED
8
wmwx=an P E S I I C I E Aldrin
fllxna Dieldrin
'I
n
'1 1
Methoxychlor
Figure 1. Chlorinated hydrocarbon pesticide mixture EXPERIMENTAL Apparatus. The instrument used for this analysis has been described earlier ( 4 ) . The gas chromatograph/mass spectrometer employed was a Finnigan Model 1015C quadrupole with a glass column and glass jet separator. The computer employed was a System,'lSO manufactured by System Industries, Sunnyvale, Calif. The Model 280 Automatic Peak Selector is manufactured by Finnigan Corporation. The four pen potentiometric recorder employed was a Rikadenki KA-40. Materials. Aroclor 1254 (polychlorinated biphenyls) is from Monsanto Chemical Company. The Halowax 1014 (chlorinated naphthalenes) is from Koppers, Industrial Chemicals Division, Verona, Pa. The pesticides were obtained from the Perrine Primate Research Branch, Environmental Protection Agency, Perrine, Fla. GC Conditions. A 5-ft x (2 mm i.d.) borosilicate glass column packed with 5 OV-17 on 60/80 Gas Chrom Q was employed for the analysis of the chlorinated hydrocarbon pesticide mixture with the Halowax 1014 and Aroclor 1254. Temperature was programmed from 180-250 " C at 8 "C/rnin. The p,p'-DDE/p,p'-DDTIPCB mixture was chromatographed on a 5-ft X 1/4-in.(2 mm i d . ) borosilicate glass column packed with 3 OV-1 on 60/80 Gas Chrom Q at 200 "C. RESULTS AND DISCUSSION Qualitative Analysis. A standard chlorinated hydrocarbon pesticide mixture (Figure 1) was mixed 1 :1 with Aroclor 1254 and Halowax 1014 to obtain Figures 2 and 3, respectively. Figures 1 to 3 are computer reconstructed chromatograms ; the summation (amplitude) of the ion intensities (1) J. A. Armour and J. A. Burke, J . Ass. Ofic.A n d . Chem., 53, 761-768 (1970). (2) Ib/d., 54, 175- 177 ( 197 1). (3) D. Goerlitz and L. Law, BuN. Enciuou. Contam. Toxicol., in
press. E. J . Bonelli. Amer. Lab., February 1971, 27-37.
(4)
FRDaLFI 1 2 S ~ I C I ME I X
R
Figure 2. Aroclor 1254-pesticide mix
of each spectrum is plotted against the spectrum number. Each pesticide is a t a concentration of 100 ng/pl. The concentration of the Halowax 1014 and Aroclor 1254 is also 100 ng/pl. One-microliter samples were injected into the GC/ MS. I n the Aroclor 1254-pesticide mix (Figure 2), there are several overlapping peaks in the region of spectrum number 84-94. Figures 4 (spectrum 85), 5 (spectrum 88), and 6 (spectrum 92) are computer plots of mass spectra stored on magnetic tape. They were identified as hexachlorobiphenyl (m/e 358), p,p'-DDD ( m / e 31S), and heptachlorobiphenyl (m/e 392), respectively. Note that there are very few interfering spectra in the three mass spectra of interest. I n the pesticide-Halowax 1014 mixture (Figure 3), the area chosen t o study was between spectrum number 75 and 85.
ANALYTICAL CHEMISTRY, VOL. 44, NO. 3, MARCH 1972
603
FESTICIcE--tFLaTo( 1014 M I X
8
Figure 3. Pesticide-Halowax 1014 mix
Figure 4. Hexachloro biphenyl identified in Aroclor 1254-pesticide mix
m
E-
-
m
FCUJX l a C R 5 7 1 C I E HlX P.P'DDD
wezl18
518-
EP-
IS&EL
6: R-
0-
H/
E
Figure 5. p , p '-DDD identified in Aroclor 1254-pesticide mix
Figure 7 (spectrum number 78) was identified as dieldrin (mie 378) while Figure 8 (spectrum number 82) was identified as a n isomer of pentachloro naphthalene (mje 298). Peak Monitoring. The separation of overlapping gas chromatographic peaks by plotting relative ion abundance Of selected masses has been described by Lindeman and Armis ( 5 ) and has since been automated by Sweeley et al. ( 6 ) , who 604
ANALYTICAL CHEMISTRY, VOL. 44, NO. 3, MARCH 1972
described a n instrument which rapidly switches the accelerating voltage between two preset voltages corresponding t o the focus of the ions at the detector. The technique of peak monitoring using the Finnigan Model 280 Automatic Peak
_ _ _ _ ~ ~ ( 5 ) L, p. Llndman alld J , L, Annls. ANAL,~HE,,,, 32, 1742 (1960). (6) C. C. Sweeleq. W , H. Elliot, and R. Rhyage, ihid.. 38, 1549 (1966).
-
Figure 6. Heptachlor0 biphenyl identified in Aroclor 1254 pesticide mix
Figure 7. Dieldrin identified in Pestici de-Halowax 1014 mix
a: R
O
U/
E
Figure 8. Pentachloro naphthalene identified in Pesticide-Halowax 1014 mix
Selector is different from the Sweeley technique in that voltages corresponding t o the mass ions of interest are applied to the quadrupole mass filter. This allows the monitoring of up to eight ion peaks over the entire mass range of the mass spect romet er . Figure 9 shows the selective monitoring of the base peak and molecular ion inp,p’-DDE and p,p’-DDT, respectively, which
were added t o a sample containing PCB’s. The PCB’s did not interfere with the analysis. Identification of a compound is achieved by comparing its retention time t o the presence of up t o eight of its characteristic mass peaks at that retention time. Quantitation is achieved by comparing the area under one or more of the eight peaks t o the area of a known amount of a standard. By peak monitoring, sensitivities in the low ANALYTICAL CHEMISTRY, VOL. 44, NO. 3, M A R C H 1972
605
Figure 9. Peak monitoring for p,p'-DDE and p,p'-DDT in a PCB mixture
nanogram and picogram range can be obtained. Figure 10 is a typical linearity curve obtained by monitoring the m/e 246 peak of p,p'-DDE; &hesample size is that amount injected o n column and shows the sensitivity obtainable with this technique. CONCLUSIONS
Components of overlapping gas chromatographic peaks in the 10-100 ng sample size can be identified by the mass spectrum obtained. It is desirable t o employ a computer which has the capacity t o store the entire analysis, process the data (such as subtract background), and present it in a form which is easy to interpret. Components of overlapping gas chromatographic peaks present in amounts less than 10 ng can be identified and quantitated by the technique of peak monitoring.
1c
I -
13
i
1 1C
IC* SAMPLE S Z E INAVEGRA'vlS
I
I
133
104
I
I I
'C
The author is grateful to James B. Knight and William Fies for assistance with the Automatic Peak Selector.
GM
Figure 10. Linearity curve monitoring the mje 246 peak of p,p'-DDE
606
ACKNOWLEDGMEhT
ANALYTICAL CHEMISTRY, VOL. 44, NO. 3, MARCH 1972
RECEIVED for review July 26, 1971. Accepted September 22, 1971.
