It appears then that the bore of the separator should be as small as possible consistent with the requirement of the inequality Equation 15, that the porosity of the wall should be small to allow the length of the separator to be large, and that the pumping speed of the ion-source region of the mass spectrometer should be small to allow the use of a small exit flow and a large ion-source pressure. Unfortunately, there are limits to the gains achievable by carrying out these procedures: for example, a very small exit flow will cause hold-up in the connecting tube and small pumping speed causes a large background spectrum to appear.
CONCLUSIONS A considerable improvement in the separation efficiency of molecular effusion separators can be made by decreasing the cross-sectional area and increasing the length. With the use of low porosity frits, useful enrichments should be obtainable with flows as low as 1ml min-' provided the massspectrometer gas flow is kept low. It should be advanta-
geous therefore to use small-bore separators with capillary columns. ACKNOWLEDGMENT I thank K. I. Grosz for making the separators and frits and V. W. Maslen for suggesting the use of an asymptotic solution of Equation 8a. LITERATURE CITED (1) J. T. Watson and K. Biemann, Anal. Chem., 36, 1135 (1964). (2) J. T. Watson and K. Biemann, Anal. Chem., 37, 844 (1965). (3) C. Brunee, H. J. Bueltemann, and G. Kappus, presented at the 17th Annual Conference on Mass Spectroscopy and Allied Topics, Dallas, Texas, 1969. (4) C. M. van Atta, "Vacuum Science and Engineering", McGraw-Hill, New York, 1965, p 39, 46. (5) J. 0. Hirschfelder, C. F. Curtis, and R. B. Bird, "Molecular Theory Of Gases and Liquids", John Wiley & Sons: New York, 1954, p 14. (6) M. Abramowltz and I. A. Stegun, Ed., Handbook of Mathematical Functions", Dover Publications, New York, 1965, Chapter 13.
RECEIVEDfor review April 14, 1975. Accepted August 18, 1975.
Pesticide Residue Analysis by Mass Fragmentography B. A. Karlhuber, W. D. Hormann, and K. A. Ramsteiner Ciba-Geigy Ltd., Agrochemicals Division, & d e . Switzerland
Up to now, the technique of mass fragmentography has not found very widespread use in trace analysis. Skinner et al. ( I ) showed for the first time the application of mass fragmentography in residue analysis, namely, the determination of PCBs along with DDE in extracts from a sewage effluent and in sturgeon ovary extracts. In a review article, Oswald et al. (2) recently mentioned the use of mass fragmentography for the quantitative analysis of various environmental agents. A comprehensive summary of coupling gas chromatography-mass spectrometry, including mass fragmentography, was recently given by Fenselau (3). In this paper, 70 references can be found. The analysis of pesticide residues depends on specific and sensitive detectors. Using multiple ion monitoring, confirmation of a compound is achieved by the gas chromatographic retention time, by the presence of one or more characteristic ion fragments of the compound, and by the ratio of the intensities of the fragments. This high degree of specificity cannot be achieved by any other known instrumental technique. Compounds not entirely separated by gas chromatography can even be determined by mass fragmentographic detection by comparing the peak heights or areas of one or more ion fragments with the corresponding peak heights or areas of known amounts of standards. To ensure efficient use of this technique for pesticide residue determinations, the following conditions have to be met: To achieve the required sensitivity, it must be possible to inject solvent volumes of up to 10 111, without impairing the proper function of the mass spectrometer. To avoid contamination of the ion source, column bleeding must be less than tolerated for other gas chromatographic detectors. The response of the mass spectrometer used as a gas chromatographic detector must be reproducible and linear in the nanogram range. 2450
The aim of the present study is to show the application and utility of gas chromatography-mass fragmentography to some typical problems in pesticide residue analysis. Some hints are given to improve the technique for trace analysis.
INSTRUMENTATION G a s C h r o m a t o g r a p h - M a s s S p e c t r o m e t e r . The instrument used was a Finnigan Model 9500 gas chromatograph coupled with a Finnigan Model 3000 D quadrupole mass spectrometer. T h e system was equipped with a glass jet separator and a two-channel programmable multiple ion monitor (Promim, manufactured by Finnigan Corporation, Sunnyvale, Calif.). Between the GLC column and separator, a T-piece connected by a solenoid valve to a vacuum line was installed to vent large volumes of solvent vapors without impairing the function of the mass spectrometer. The construction of this automatic venting valve assembly was described by Karlhuber et al. ( 4 ) . A similar system was recently described also by Kuehl et al. (5). The experimental parameters for the mass spectrometer detector used were as follows: electron energy, 70 eV; beam current, 0.4-0.6 mA; electron multiplier voltage, 1.0-1.2 kV; preamplifier, A/V; interface oven temperature, 220 O C ; transfer line temperature, 220 " C ; manifold temperature, 120 OC; and helium flow rate, 25 ml/min. The signals were recorded on a two channel W W recorder model 1200 (W W Electronic AG, Basle, Switzerland). Gas C h r o m a t o g r a p h i c D e t e c t o r s . For comparative studies, the following two GLC-detectors were used: Electron capture detector (Tswett, OKBA, Dzershinsk Gorkowskoj, Oblasti, USSR) attached to a Tswett 5-68 gas chromatograph and Coulson electrolytic conductivity detector (Tracor Instruments, Austin, Texas) attached to a Varian 1700 gas chromatograph (Varian Aerograph, Walnut Creek, Calif.). The experimental parameters for these detectors were as follows. Electron capture detector: detector, 239Pu foil; carrier gas, Nitrogen, 60 ml/min; injection port temperature, 240 O C ; and detector temperature, 270 O C . For the Coulson electrolytic conductivity detector: reactant gas, hydrogen, 60 ml/min; carrier gas, helium, 70 ml/min; transfer line temperature, 240 OC; furnace temperature, 780 " C ; catalyst, Ni; and scrubber, Sr(OH)2.
ANALYTICAL CHEMISTRY, VOL. 47, NO. 14, DECEMBER 1975
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Table I. ReproducibilityD Base peak m / e 200, m m peak height
Injection No.
1 2 3
29 29 27
4 5
27 28 28 27 29 28 27 28
6 7 8 9
10 11 a Standard solution: 1 ng/pl atrazine. sample 10.
1 hr after injection of
Figure 1. Total ion monitor chromatogram (A) 100 ng GS 26571, (5) 100 ng terbuthylazine, (C)Mixture of GS 26571 and terbuthylazine 100 ng each. Glass column (1 m X 2 mm i.d.) packed with 2% neopentyl glycol succinate on Chromosorb G, 210 O C , range 50-250 amu
RESULTS
Verification of Linearity a n d Reproducibility. The linear dynamic range of our instrument was checked with standard solutions of atrazine over three orders of magnitude (100 pg to 100 ng) whereby the ions at mle 200 (base peak) and mle 215 (molecular ion) were monitored. The peak heights of both recorded traces were plotted vs. the amount injected. The slope and intercept of the regression line for the base peak, rnle 200, were calculated by a desk top computer. The coefficient of correlation was 0.9991, the slope 1.2, and the intercept 0.24 cm. From 11 replicate injections of 1 ng of atrazine, the relative standard deviation was calculated to be f3%. Injection of sample 11 was performed one hour after injection of sample 10 (Table I). Separation of Unresolved G a s Chromatographic Peaks by Mass Fragmentography. The selectivity of the mass fragmentographic detector was demonstrated by simultaneous determination of the following two triazines: terbuthylazine (4-tert-butylamino-2-chloro-6-ethylaminos -triazine) and GS 26571 (2-amino-4-tert-butylamino-6-me- Flgure 2. Mass fragmentogram of terbuthylazine and GS 26571 thoxy-s-triazine). The total ion monitor chromatogram (A) 10 ng GS 26571, (5) 10 ng terbuthylazine. (C)Mixture of GS 26571 and terbuthylazine 10 ng each. Glass column (1 m X 2 mm i.d.) packed with 2% (mass range 50-250 amu) resulted in the same retention neopentyl glycol succinate on Chromosorb G, 220 OC, isothermal. Recording: time for both triazine compounds (Figure 1).By monitortop trace, m/e 174 (terbuthylazine); bottom trace, m/e 183 (GS 26571) ing each channel of the Promim at the base ion of each triazine, the detection and quantitation was tried in one single aqueous ammonia. After centrifuging, the aqueous extract chromatographic run. was injected directly into the GLCIMS. The result of monitoring different base ions for the siThe determination of 2-methoxyethanol in olive prodmultaneous determination of the above mentioned triazucts failed with any specific GLC-detector normally used in ines terbuthylazine and GS 26571 is shown in Figure 2. residue analyses, as this compound does not contain hetero Chromatogram C clearly demonstrates that 10 ng each of atoms besides oxygen. Therefore use of the mass spectromthe two compounds can easily be determined although the eter as a GLC detector was mandatory. The molecular ion gas chromatographic retention times are identical. at mle 76 is weak. Therefore the base peak at mle 45 was Determination of Methoxyethanol i n Olive Oil a n d chosen for the mass fragmentographic detection of the Olive Cakes. Methoxyethanol originates from CGA 13586, compound. For verification purposes in case of high residue the active ingredient of Alsol, an olive abscission agent, levels, the molecular ion mle 76 was recorded on the second which was hydrolyzed according to the following formula: channel of the Promim. H20 Figure 3 shows the corresponding chromatogram, a stan(CH~OCHZCHZO)&~~-CHZCHZC~ dard injection of 2-methoxyethanol, a fortified sample, and an untreated sample of olive oil. As the concentration of 23 C H ~ O C H Z C H ~ O HSiOz,, HCl + CH2=CH2 methoxyethanol was low, no molecular peak was detectThe principle of the residue analytical method was as folable. However, the sensitivity of the rnle 45 trace was suffilows: Deep frozen olives were ground with Dry Ice, further ciently high and there was no interference from the olive homogenized, and centrifuged. The water which contained oil. the methoxyethanol was cleaned up on a Bio-Gel P-2 colDetermination of Bromofenoxim Residues i n Hops. Bromofenoxim is hydrolyzed in alkaline medium to 3,5umn (Bio-Rad Laboratories, Richmond, Calif.). The eluate from this column was directly injected into the gas chromadibromo-4-hydroxybenzoic acid. Residues of this comtograph-mass spectrometer. Olive oil was shaken with pound in hops were determined according to the following
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ANALYTICAL CHEMISTRY, VOL. 47, NO. 14, DECEMBER 1975
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R a w
g 0
L L
w
E e U
time
Figure 5. Gas chromatogram of sewage water
:ime
Figure 3. Mass fragmentogram of methoxyethanoi
(A) Mixture of prometryn (l), atrazine (2) and simazine (3), 100 ng each: (E) sewage water 12 5-mg aliquot. Couison electrolytic conductivity detector (nitrogen specific). Glass column (1 m X 3 mm i.d.) packed with a mixture of 2 % neopentyl glycol succinate and 2% free fatty acid phase 1.1 on Chromosorb G, 195 OC isothermal
dibromo-4-hydroxybenzoic acid methyl ester was impossible. The mass spectrum of 3,5-dibromo-4-hydroxybenzoic acid methyl ester showed the molecular peak at m / e 324 and the base peak at m / e 293, respectively. When these peaks were monitored for mass fragmentographic detection of the compound, a limit of detection of 0.05 ppm in hops extracts was reached as illustrated by the chromatogram in w Figure 4. C Q Examination of Apparent Atrazine Residues in Sewage Water. Water samples were cleaned up according to Ramsteiner et al. (6). An aliquot of sewage water was neutralized and extracted with dichloromethane. The extract was further cleaned up by passage through a alumina column. After concentration, atrazine was injected into a gas chromatograph equipped with a Coulson electrolytic conductivity detector and GLC/MS. Injection of a 12.5-mg sewage water aliquot into a gas chromatograph equipped with the nitrogen specific Coulson electrolytic conductivity detector showed a peak with the same retention time as atrazine (Figure 5B).From a standard injection (Figure 5 A ) , an apparent atrazine concentration of 5.5 ppm in the sewage sample was calculated. No atrazine was expected in this sample. The value found Flgure 4. Mass fragmentogram seemed extremely high and the sample was reinjected on (A) 1 ng 3,5dibromo-4-hydroxybenzoic acid methylester: (E)Treated hops the GLC with mass fragmentographic detection. No peak sample, 2-mg aliquot: (C) Check sample, 2-mg aliquot. Glass column (1 rn X showed up in the chromatogram at the retention time of 2 mm i.d.) packed with 2% SE 30 on Chromosorb G, 160 OC, isothermal. Reatrazine, indicating that there was less than 0.01 ppm of cording: top trace, m / e 293; bottom trace, m/e324 atrazine in the sewage water. The peak in the nitrogen specific chromatogram, therefore, was a nitrogen-containing analytical procedure: The hops were extracted with a mixinterference with the same retention time as atrazine. In ture of ethyl ether and formic acid. The extract was alkalithis case, an alternative solution of the problem would have nized with aqueous sodium hydroxide. The ether was evapbeen to look for a column which was able to separate atraorated and the aqueous solution refluxed to hydrolyze the zine and the interference. However, with the specific mass bromofenoxim. Neutral and basic interferences were then fragmentographic detector, the problem could be solved removed by extraction with dichloromethane. The basic solution was acidified and the 3,5-dibromo-4-hydroxybenzoic much easier and faster. acid extracted into dichloromethane. After methylation LITERATURE CITED with diazomethane, the extract was further cleaned up by (1) R. F. Skinner. W F Fies. and E. J. Bonelli. "Finniaan Vol 3. silica gel column chromatography. The solution was con- Soectra". . No. l(1973). centrated and injected into a gas chromatograph equipped (2) E. 0. Oswald, P. W. Albro, and J. D. McKinney, J. Chromatogr., 98, 449 with an EC-detector or into the GLC/MS. 119741 .. .,_ C. Fenselau, Appl. Spectrosc., 28, 305 (1974). The determination of 3,5-dibromo-4-hydroxybenzoic (3) ( 4 ) B. Karlhuber, K. Ramsteiner, W. D. Hormann, and W. Simon, J. Chromaacid, the hydrolysis product of bromofenoxim, in hops pretogr., 84, 387 (1973). (5) D. W. Kuehl, G. E. Glass, and F. A. Puglisi, Anal. Chem., 46, 804 (1974). sented a difficult problem. Standard samples of the ester (6) K. Ramsteiner, W. D. Hormann, and D. 0. Eberle, J. Assoc. Off. Anal. were well detected with high sensitivity by using an elecChem.. 57, 192 (1974). tron capture detector. If, however, hops samples had to be analyzed, the chromatogram showed that, even after the RECEIVEDfor review March 25, 1975. Accepted July 28, clean-up procedure described above, a quantitation of 3,s- 1975.
(A) 2 ng 2-methoxyethanol, (E)Spanish olive oil fortified with 1 ppm of active ingredient, (C) Control (untreated) olive oil, 5-mg aliquot injected. Glass column (1 m X 2 mm i.d.) packed with Porapak Q, 190 OC. isothermal. Recording: top trace, m / e 45; bottom trace, m l e 76
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ANALYTICAL CHEMISTRY, VOL. 47, NO. 14, DECEMBER 1975
