Anal. Chem. 1984, 56, 1277-1281 Sebedio, J-L.; Ackman, R. G. J. Chromatogr. Scl. 1981, 19, 552-557. Harvey, H. R.; Patton, J. S. Anal. Biochem. 1981, 116, 312-316. Kaitaranta, J. K.; Nicoiaides, N. J. Chromatogr. 1981, 205, 329-347. Ranny, M.; Zbirovsky, M.; Blahova, M.; Ruzicka, V.; Truchlik, S. J. Chromatogr. 1982, 2 4 7 , 327-334. Peterson, B. J. Chromatogr. 1982, 242, 313-322. Foot, M.; Clandinin, M. T. J. Chromatogr. 1982, 241, 428-431. Innis, S. M.; Clandinin, M. T. J . Chromatogr. 1981, 205, 490-492. Christie, W. W.; Hunter, M. L. J. Chromatogr. 1979, 171, 517-518. Kramer, J. K. G.; Fouchard, R. C.; Farnworth, E. R. J. Chromatogr. 1980, 198, 279-285. Crane, R. T.; Goheen, S.C.; Larkin, E. C.; Rao, G. A. Lipids 1983, 18, 74-80. Farnworth, E. R.; Thompson, B. K.; Kramer J. K. G. J. Chromatogr. 1982, 240, 463-474. Paradis, M.; Ackman, R. G. J . Fish. Res. Board Can. 1977, 3 4 , 2156-2163. Lewis, R. W. Limnol. Oceanogr. 1989, 14, 35-40. Lee, R. F.; Nevenzel, J. C.; Paffenhofer, G.-A. Mar. Blol. 1971, 9 , 99-108. Velimirov, B. Mar. Ecol. 1982, 3 , 97-107. Oisen, C. R.; Cutshall, N. H.; Larsen, I . L. Mar. Chem. 1982, 1 1 , 501-533. Whittle, K. J.; Hardy, R.; Mackie, P. R.; McGiII, A. S.Philos. Trans. R . SOC.London, Ser. B 1982, 297, 193-218. Sullivan, K. F.; Atlas, E. L.; Giam, C.-S. Environ. Scl. Techno/. 1982, 16, 428-432. Simkiss, K. J. Mar. Biol. Assos. U . K . 1983, 6 3 , 1-7. Florence, T. M.; Lumsden, B. G.; Fardy, J. J. Anal. Chlm. Acta 1983, 151, 281-295.
(23) (24) (25) (26) (27) (28) (29) (30) (31) (32) (33) (34) (35) (36) (37) (38) (39) (40)
1277
Goutx, M.; Saliot, A. Mar. Chem. 1980, 8 , 299-318. Kennicutt, M. C.; Jeffrey, L. M. Mar. Chem. 1981, 10, 367-387. Kennicutt, M. C.; Jeffrey, L. M. Mar. Chem. 1981, 10, 389-407. Ehrhardt, M.; Bouchertall, F.; Hopf, H-P. Mar. Chem. 1982, 1 1 , 449-48 1. Parrish, C. C.; Organ, G.; Ackman, R. G., unpublished work. Forney, F. W.; Markovetz, A. J. J. Lipid Res. 1971, 12, 383-395. Rouser, 0.; Kritchevsky, G.; Simon, G.; Nelson, G. J. Lipids 1987, 2 , 37-40. Gagosian, R. B. Limnol. Oceanogr. 1978, 2 1 , 702-710. Dallas, M. S.J. J . Chromatogr. 1965, 17, 267-277. Parrish, C. C.; Ackman, R. G. Llplds 1983, 18, 563-565. Adams, G. M.; Sallee, T. L. J. Chromatogr. 1971, 5 4 , 136-140. Bromly, J. H.; Roga, P. J. Chromatogr. Sci. 1980, 18, 606-613. Phillips, F. C.; Erdahi, W. L.; Privett, 0. S.Lipids 1982, 17, 992-997. Banks, F. B. J. Chromatogr. 1983, 254, 247-255. Parrish, C. C.; Ackman, R. 0. Lipids, in press. Llebezeit, G.; Bolter, M.; Brown, I. F.; Dawson, R. Oceanol. Acta 1980, 3 , 357-382. Parrlsh, C. C.; Delmas, R. P.; Ackman, R. G., unpublished work. Hammon, E. W. J . Chromatogr. 1981, 203, 397-403.
RECEIVED for review December 7,1983. Accepted February 24,1984. This work was supported by grants from the Natural Sciences and Engineering Research Council of Canada to R. G. Ackman and to P. J. Wangersky. C. C. Parrish also acknowledges support by an Izaak Walton Killam Memorial Scholarship.
Chemical Class Separation of Organics in Shale Oil by Thin-Layer Chromatography Timothy G. Harvey, Trevor W. Matheson,* and Kerry C. Pratt CSIRO Division of Materials Science, Catalysis and Surface Science Laboratory, University of Melbourne, Parkville, 3052, Victoria, Australia
Thin-layer chromatography (TLC) has been applied to the chemlcal class fractlonatlon of shale oil. The chromatographic procedure gives rapld and reproducible separation of the oll Into 14 fractions, without requlrlng prlor extractlon of asphaltenes, aclds, or bases. The oll was adsorbed on slllcatoated TLC plates and eluted with n-pentane and n-pentane/dlethyl ether to separate the nonpolar and polar components, respectlvely. The prlnclpal compound types resolved Included n-alkanes, alkenes, mono-, hydro-, dl-, and polyaromatlcs, nltrlles and ketones, hydroxyl aromatlc hydrocarbons, and nitrogen heterocycles. Compound ldentlflcatlon was by GC/MS, supplemented by Infrared spectrometry. The method slgnlflcantly decreases the analysis time required for chemical class fractionation.
The search for alternative energy sources has led to intensified studies in the characterization of materials such as heavy petroleum fractions, coal liquids, shale oils, and tar sands. These materials are invariably complex and contain a large range of hydrocarbon types together with a high percentage of polar and nonpolar heteroatomic compounds. The analysis of these complex materials requires extensive fractionation before identification and quantitation of individual compounds or classes can be attempted. The basis of most separation schemes traditionally has been column chromatography. The extensively used (1-5) U.S. Bureau of Mines, American Petroleum Institute (USBM-API)
method (and a derivative, the SARA method) combines ionexchange and coordination-complex chromatography with alumina or combined silica-alumina columns to separate acidic, basic, and neutral nitrogen compounds, saturated hydrocarbons, and aromatic hydrocarbons. Classical chromatographic separations employing both single- and dualpacked silica, alumina, and silica/alumina columns have been applied to heavy petroleum fractions, shale oils, and coalderived material (6-14). However, the inherent problems of column chromatography, such as the length of time required, the large volumes of solvents used, and the general inefficiency of the separations, remain. The greater efficiency of high-performance liquid chromatography (HPLC) should decrease analysis time, allow separation of high boiling fractions, and give cleaner class separations by comparison with conventional liquid chromatography. Early studies showed that petroleum (15) and other feedstocks (16)could be rapidly separated into saturates, aromatics, and polars by using activated silica as the stationary phase. Selectivities were improved by the development of bonded phases (17,18), the application of switching techniques (19),and, recently by the introduction of high-resolution microcapillary columns (20). Despite the success enjoyed by HPLC in resolving compounds within a chemical class and model compound mixtures, these separations have not translated to complex oils. Overlap of classes, such as saturates/olefins, and aromatics (mono-, di-, and polyaromatics), remains a problem, usually requiring a second chromatographic run to obtain the desired fractionation.
0003-2700/84/0356-1277$01.50/00 1984 American Chemical Society
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The class fractionation of fuel oils by thin-layer chromatography (TLC) has not been extensively reported. Components of petroleum products have been identified by comparison with the Rf values of standard materials (21,22),while column chromatography followed by TLC has been used to separate and identify the polyaromatic hydrocarbons in shale oil (23). A comparison has been made between thin-layer chromatography and column chromatography as a technique €or separating the nonaromatic hydrocarbons, aromatic hydrocarbons, and polar compounds present in sedimentary material (24,25). The technique has been employed for the separation of coal liquids (26,27),and the fractionation of an Estonian shale oil into five classes, including olefins and neutral oxygen compounds (28). The use of TLC can circumvent many of the problems encountered in the separation techniques discussed earlier. In this paper we describe the application of TLC to the separation of a shale oil into 14 component classes.
EXPERIMENTAL SECTION Shale Oil. Shale oil (boiling range up to 400 "C) produced by the Lurgi-Ruhrgas retorting process from Rundle oil shale (Queensland, Australia) was supplied by Southern Pacific Petroleum, N.L. Analysis gives the following: C, 85.4%;H, 11.5%; N, 1.1%;0, 1.1%;ash, 0.2%. Reagents. 2,7-Dichlorofluorescein was obtained from BDH and methanol (AR grade) from May and Baker. Diethyl ether, dichloromethane, and n-pentane (Nanograde quality) were supplied by Mallinkrodt. All reagents were used as received. TLC Separations. Silica gel (Merck Kieselgel 60 G) was coated manually on 20 cm X 20 cm glass plates in a 0.75 mm layer and dried (110 "C for ll/zh) and the layer cleaned by elution with CH2C12. The top 2 cm of the silica layer, containing any organic impurities from the plate, was then removed. The plates were stored in the open air and used without further activation. Whole shale oil (-150 mg and -200 mg for nonpolar and polar separations, respectively) was applied undiluted to the TLC plate by use of a drawn out Pasteur pipet to give a line of sample -2 cm from the base of the plate. (Care is required since the silica layer is soft and easily damaged). Development with n-pentane (to elute the nonpolar compounds) or n-pentaneldiethy1 ether (5:l v/v) (to separate the polar components) usually took 20-25 min. Bands were visualized by spraying with a 2,7-dichlorofluorescein solution (29) (0.2% in MeOH) and irradiating with UV light. The dye was found to give best results with a development time of 10-15 min. During this time the plates were stored in a TLC developing tank saturated with pentane vapor to minimize evaporative losses. The separate bands, which appeared purple or blue under UV light were carefully scraped from the glass backing and the fractions recovered by washing the silica with CH2C12(2-3 mL) or, for polar bands, CH2C12-MeOH (1:l v/v; dried over MgSOI). In the latter case, the volume was reduced and the fractions were eluted through a short MgS04 column with CHzC12(occasionally with some MeOH). This eliminated any water and traces of the dye. Finally, all fractions were reduced in volume under a gentle stream of N2 GC-GC/MS. Preliminary gas chromatographic analyses were carried out on a Varian Model 3700 instrument using flame ionization detection. Gas chromatography/mass spectrometry analyses were carried out on a Hewlett-Packard 5995A machine equipped with either a 50 m X 0.2 mm i.d. silica SE-30 WCOT column or a 50 m x 0.22 mm i.d. silica BP-1 (bonded phase) WCOT column. Compound identifications were made by interpretation of the fragmentation patterns and by comparison with the EPA/NIH library (except where otherwise noted). Retention times were used to confirm assignments where standard compounds were available. Infrared Spectra. Infrared spectra were obtained from smears on NaCl plates, using a Pye-Unicam SPS-300 infrared spectrometer.
Table I. Chemical Class Separation of Shale Oil by TLC eluting solvent a
1O'Rf
82 76
major chemical class
P P P
n-alkanes branched and cyclic hydrocarbons 70 alkenes 60 P monoaroma tics 55-50 P hydroaromatics 44-36 P diaromatics 35-21 P polyaromatics 50 PE nitriles, methyl ketones 33 PE nitriles, ketones 27 PE phenols, indanols, naphthols 22 PE 16 PE cycIic unsaturated ketones 6 PE basic nitrogenous compounds 0 PE highly polar material a Key: P, n-pentane; PE, pentaneidiethyl ether. Tentative identification, (1)
A
&
J
4
(lv)
W
4n
.-
Y
! 3 I ' .
60
100
i1-alkene
150
200
\
i
250
280
TEMPERATURE (OC)
Figure 1. Gas chromatograms of selected fractions of shale oil: conditions were 25 m X 0.2 mm i.d. OV-101 vitreous silica WCOT column, temperature programmed from 40 (held 1 min) to 280 'C at 10 " C min-'; (m) dichloromethane solvent, (0)solvent impuiw; (i) whole shale oil, (ii) total n-alkane fraction with the carbon numbers of the homologous series marked, (iii) monoaromatic fraction with the carbon numbers marked for the n-alkyl side chains of the major substituted benzene series, (iv) polyaromatic fraction with the identified compounds (GCIMS) listed.
NMR. NMR spectra were obtained of CDCl, solutions, using a JEOL FX-100 FT-NMR spectrometer. RESULTS AND DISCUSSION The separation achieved and the chemical classes resolved in this work are presented in Table I. Some representative
ANALYTICAL CHEMISTRY, VOL. 56, NO. 8, JULY 1984
I
50
100
1279
I
200
150
250
TEMPERATURE (OC)
,oo ............................................................................. (11)
1
xg 226S~m-~
V
17 1Ocm-1
(Ill) L
J-
*
2400 288
Y
S65cm-’ 1850 1000 cm-1
850 cm-1
Figure 3. Partial infrared spectra of fractions showing (i) aliphatic C F N , (ii) C=O (1650-2400 cm-l), and (Hi) olefinic (850-1000 cm-’) regions. of isopropyl- and sec-butylbenzene served to identify the 2-phenylalkanes. The monoaromatics displayed characteristic base peaks at m/e 91, 92,105, 106, 119, or 120. The bulk of the hydroaromatics was made up of indanes and tetralins substituted with up to 12 and 11carbon atoms, respectively. Indane itself was identified (by its mass spectrum and retention time) and several indane homologues were easily assigned by their distinctive m/e 117 base peak. A number of tetralin homologues were also recognized by their characteristic mass spectral patterns, but the parent, tetralin, was not observed. Highly substituted compounds (with base peaks of m/e 131,145, and 159) were more difficult to assign as either indanes or tetralins. A series of monounsaturated long chain (up to 15 carbon atoms) monoaromatics was also present. These were probably l-phenyl-4-alkenes, which have been observed by other workers (9). The main constituents of the diaromatic fraction were 1and 2-substituted naphthalenes (with base peaks of m/e 141, 155, 156, 169, and 1701, most of which had from one to six carbon side chains. Significant quantities of both biphenyl and acenaphthene and their homologues (to six carbon substitution), as well as small amounts of indenes, were also found. The identification of 1-and 2-methylnaphthalene, biphenyl, and acenaphthene was confirmed by use of standards; homologues were assigned on the basis of fragmentation patterns. The polyaromatic fraction contained mainly tri- and tetraaromatics and their homologues (Figure 1). Unlike the mono- and diaromatic compounds, only short side chains (up to three carbon atoms) were detected as substituents on the polycyclic aromatic compounds. These compounds are easily distinguished by their simple mass spectra, which are normally dominated by strong M+ ions. The assignments of fluorene, phenanthrene, anthracene, fluoranthene, and pyrene were verified by coinjection of standards. The polar components present in the oil remained in the base line at this stage (Figure 4). Fractionation of this material was achieved by using n-pentaneldiethy1 ether ( 5 1 v/v) as eluant. The bulk of the fiist band of the polar compounds was made up of two major homologous series, aliphatic nitriles and methyl ketones, which ranged from C8to C30and C, to C31, respectively. These compounds have been detected previously in shale oil (9,28). Small quantities of phenyl ketones were also present. The two major series were identified mass spectrally and by the retention times of undecane- and dodecane-nitrile and 2-tridecanone. Further evidence was provided by an infrared spectrum of the fraction (Figure 3)
ANALYTICAL CHEMISTRY, VOL. 56, NO. 8, JULY 1984
1280
.
A
I
1.
i
1 1
B IC
li
J
60
100
150 TEMPERATURE P C )
200
2 50
Figure 4. Gas chromatograms of polar fractions: conditions as in Figure 2; (i) total polar fraction, (ii) total acid fraction after TLC of (I). which displayed bands a t 2255 cm-l (w, aliphatic C=N) and 1710 cm-l (s; C=O). The following band contained three short series of compounds, whose functionalities appeared to include nitriles and carbonyls. The structures of these compounds have not yet been elucidated. The next two fractions contained most of the acidic components of this shale oil. These included phenol and its homologues (with up to seven carbon atoms in side chains), indanols and their homologues (to two carbon atom substitution), and one and two carbon atom substituted naphthols. There was a distinct partitioning of phenol and methylphenols between these two bands on the basis of substituent shielding of the hydroxyl group. The effect of shielding on the strength of adsorption of phenols on silica has also been noted elsewhere (28). The acidic components were identified from mass spectral and retention data accumulated from earlier work and published elsewhere (33). The next (minor) band was composed mainly of cyclic unsaturated ketones (cyclopentenones, cyclohexenones) with substitution in positions ortho to the carbonyl group. These components were identified by mass spectra data. Small amounts of substituted pyridines and quinolines were also present. The final band to separate was composed almost completely of basic nitrogen-containing compounds. Pyridine and quinoline homologues (with up to six and three carbon atoms in side chains, respectively) make up the bulk of this band. The alkylpyridines and substituted quinolines displayed strong molecular ions (homologues of m / e 93 and 129, respectively) with little fragmentation, indicating short chain lengths. The identifications were reinforced by retention data from earlier work (33). The presence of 5,6,7,8-tetrahydroquinoline, quinoline and isoquinoline was confirmed by the retention times of standards. One quinoline benzologue ( m / e 179) was also detected. Minor components of this band included cyclopentenones and cyclohexenones substituted in positions remote from the carbonyl group. The material which remained on the base line was complex. Some small pyrroles and indoles were identified and spectroscopic studies (GC/MS and IR) indicated the presence of polyfunctional material. However this material amounted to less than 1% of the oil. The TLC method reported here requires no time-consuming prior extractions to remove asphaltenes or acids and bases. The short contact time of the sample with the support reduces the possibility of artifact formation (13) or irreversible absorption (14).The nonsequential nature of the fractionation allows one, or several, of the chemical classes to be separated
quickly and so this method is better suited than other fractionation schemes to monitor changes in an oil through an upgrading process. The compound types separated in this study, in particular the acids, and bases, compared favorably with those obtained from the same shale oil by more conventional fractionation schemes (9, 33). The method described has also been applied to a number of hydrotreated shale oils, a crude oil (from the Halibut field in the Bass Strait), and bituminous and brown coal liquids. Particular care was taken in this work to minimize the loss of light material from the oil fractions. Low boiling solvents were used throughout but the observation of losses during evaporation precluded taking the fractions, other than the polycyclic aromatics, to constant weight. The technique was semiquantitative under these conditions although quantitative fractionation of heavier material by TLC has been reported (25,27). Sufficient quantities were recovered of most fractions to enable detailed analysis by GC, GC/MS, IR and FT NMR. The fractions were reproducibly separated and removed from the TLC plate without cross-contamination. The cleanness of separation was monitored by GC; typical results are shown in Figures 1 and 2, with no evidence of alkene/alkane or alkene/monoaromatic overlap. Thin-layer chromatography has been shown to give rapid separation with high resolution of shale oil into its major chemical classes. The fractionation of this high boiling (up to 400 OC) shale oil (as well as other oils) demonstrates the applicability of the technique to the chemical class separation of a wide range of other high boiling material such as heavy petroleum fractions, coal liquids, and tar sands. Features of the thin-layer chromatographic technique are the minimal amounts of sample and of solvents required, the excellent separations, and the short analysis time.
ACKNOWLEDGMENT We thank Southern Pacific Petroleum N.L. for the gift of shale oil samples and T. V. Verheyen and M. Strachan for the coal liquids and crude oil samples. Registry No. Indane, 496-11-7; 1-methylnaphthalene,90-12-0; 2-methylnaphthalene, 91-57-6; biphenyl, 92-52-4;acenaphthene, 83-32-9;phenol, 10895-2; 5,6,7,&tetrahydroquinoline,10500-57-9; quinoline, 91-22-5; isoquinoline, 119-65-3. LITERATURE CITED Altgelt, K. H., Gouw, T. H., Ed., "Chromatography in Petroleum Analysis"; Dekker: New York, 1979; Chapters 9 and 10. Jewell, D. M.; Weber, J. H.; Bunger, J. W.; Plancher, H.; Latham, D. R. Anal. Chem. 1972, 4 4 , 1391. McKay, J. F.; Amend, P. J.; Harnsberger, P. M.; Cogswell, T. E.; Latham, D. R. Fuel 1981, 60, 14. Bunger, J. W.; Thomas, K. P.; Dorrence, S. M. Fuel 1979, 58, 183. Galya, L. G.; Suatoni, J. C. J . L l q . Chromatogr. 1980, 3 , 229. Shue, F. F.; Yen, T. F. Anal. Chem. 1981, 53, 2081. Hirsch, D. E.; Hopkins, R. L.; Coleman, H. J.; Cotton, F. 0.;Thompson, C. J. Anal. Chem. 1972, 4 4 , 915. Sawatzky, H.; George, A. E.; Smiley, G. T.; Montgomery, D. S. Fuel 1976, 55, 16. Regtop, R. A.; Crlsp, P. T.; Ellis, J. Fuel 1982, 67, 185. Schiller, J. E.; Mathiason, D. R. Anal. Chem. 1977, 4 9 , 1225. Whitehurst, D. D.; Butrlll, S. E., Jr.; Derbyshire, F. J.; Farcasiu. M.; Odoerfer, G. A.; Rudnick, L. R. Fuel 1982, 6 7 , 994. Farcasiu, M. Fuel 1977, 56, 9. Holmes, S. A,; Thompson, L. F. Oilshale Symp. Proc. 1981, 14, 235. Later, D. W.; Lee, M. L.; Bartle, K. D.; Kong, R. C.; Vassilaros, D. L. Anal. Chem. 1981, 53, 1612. Stevenson, R. J . Chromatogr. Scl. 1971, 9 , 257. Suatoni, J. C.; Swab, R . E. J . Chromatogr. Sci. 1976, 14, 535. Matsunaga, A,; Kusayanagi, S. Prepr. Pap.-Am. Chem. Soc., Div. Fuel Chem. 1981, 26,59. Miller, R. Anal. Chem. 1982, 5 4 , 1742. Alfredson, T. V. J . Chromatogr. 1981, 218, 715. Hlrata, Y.; Jinno, K. HRC CC J . High Resolut. Chromatogr. Chroma tagr. Commun. 1983, 6 , 196. Killer, F. C. A,; Amos, R. J . Inst. Pet. 1966, 52,315. Mathews, P. J. J . Appl. Chem. 1970, 20,87. Hurtubise, R. J.; Phillip, J. D. Anal. Chlm. Acta 1979, 710, 245. Gearing, J. N.; Gearing, P. J.; Lytle, T. F.; Lytle, J. S. Anal. Chem. 1978, 5 0 , 1833. Huc, A. Y.; Roucachd, J. G. Anal. Chem. 1981, 53, 914.
-
Anal. Chem. 1984, 56, 1281-1285 Artr, R. J.; Schweighardt, F. K. J . Ll9. Chromafogr. IS80, 3 , 1807. Selucky, M. L. Anal. Chem. 1983, 55, 141. Klesment, I. J. Chromafogr. 1974, 97, 705. Hettmann, E., Ed. “Chromatography: A Laboratory Handbook of ChromatOaraDhlC and ElectroDhoretic Methods”, 3rd ed.; Van NostrandReinthd! New York, 1975; p 179. (30) Strothers, J. B. “Carbon-13 Nmr Spectroscopy”; Academic press: New York, 1972; p 70. (31) Latter, S. R.; Solli, H.; Douglas, A. G.; DeLange, F.; DeLeeuw, J. W. Nature (London) 1979, 279, 405. (32) Bellamy, L. J. “The Infrared Spectra of Complex Molecules”, 3rd ed.;
(26) (27) (28) (29)
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Chapman and Hall: London, 1975; Vol. 1. (33) Ben, G. B.; Harvey, T. G.; Matheson, T. W.; Pran, K. C. Fuel 1983, 62, 1445.
RECEIVED for review July 11, 1983. Resubmitted December 12,1983. Accepted February 21,1984. This work was supported by the National Energy Research, Development and Demonstration Council of Australia.
Determination of Aldicarb, Aldicarb Oxime, and Aldicarb Nitrile in Water by Gas ChromatographyIMass Spectrometry Michael L. Trehy and Richard A. Yost* Department of Chemistry, University of Florida, Gainesville, Florida 32611 John J. McCreary Department of Environmental Engineering Science, University of Florida, Gainesville, Florida 32611
A technlque for the analysls of aldlcarb and two of Its degradation products is described, The use of a short caplilary column coupled to a mass spectrometer Is found to facllltate the analysis of the thermally labile carbamate pestlclde. Methane and lsobutane chemlcai ionization reagent gases are evaluated. The llmlts of detection for aldlcarb, aidlcarb oxime, and aldlcarb nltrlle are 0.3 ng, 1.2 ng, and 0.15 ng, respectively. Application of the technlque to the study of the fate of aldlcarb In anaeroblc groundwaters Is described. Aldicarb Is found to slowly hydrolyze to aidicarb oxime in sterile anaerobic groundwater at pH 8.2; in the presence of a hlgh concentrationof anaeroblc mlcroorganisms, however, aldlcarb rapidly degrades to aidicarb nltrlie.
Aldicarb is a carbamate pesticide manufactured by Union Carbide and sold under the trademark Temik. Analysis for aldicarb and its degradation byproducts is of concern since aldicarb is extensively used in agriculture and has been detected in groundwaters in agricultural areas (1). This report describes a GC/MS method to selectively detect aldicarb (I) (2-methyl-2-(methylthio)propanal0-[(methylamino)carbonyl]oxime), aldicarb nitrile (11) (2-methyl-2(methylthio)propanenitrile), and aldicarb oxime (111) (2methyl-2-(methylthio)propanaloxime). Aldicarb oxime and aldicarb nitrile are found to be the major byproducts of aldicarb formed in spiked anaerobic water samples.
c H3
H
I
I
CH,SCCH=NOCNCH,
I
I1
0
CH, 1
CH,
I
CH3SCCSN
I
CH,
I1
CH3
I
CH,SCCH=NOH
I
c H, 111
Methods which have been reported for the analysis of aldicarb include thin-layer chromatography (TLC) (2,3), liquid chromatography (LC) with various detectors (mass spectrometer (4), ultraviolet detector ( 5 ) )and postcolumn derivitization and fluorometric detection (6, 7)), and gas chromatography (GC) with various detectors (Hall detector (8), mass spectrometer (GC/MS) (9), flame ionization detector (2), and esterification and detection with an electron capture detector (10)). Only the LC and TLC methods avoid degra0003-2700/84/0356-1281$01.50/0
dation of aldicarb. Aldicarb is thermally labile and rapidly degrades in the injection port or on the column in all the GC methods reported. The thermal degradation product of aldicarb has been identified as aldicarb nitrile by matching the retention time with that of a synthesized standard on a Carbowax 20M packed column (2). Mass spectra obtained in this study for the thermal degradation of aldicarb observed on a 30-m Carbowax 20M capillary column are consistent with their identification. The use of short columns to facilitate faster analyses and to avoid thermal degradation has been reported (11,12). A 1-m SE-30 packed column has been used for the analysis of carbaryl residues in foods with some success (12). Here we show that this approach can minimize degradation of aldicarb, permitting the detection of aldicarb itself. A major drawback to the use of GC methods for the analysis of aldicarb is that aldicarb not only degrades during the GC analysis to aldicarb nitrile, but may also degrade chemically in the environment to aldicarb nitrile. Thus, if aldicarb nitrile is not removed prior to GC analysis by a Florisil separation (13), this environmental degradation product will give a positive interference for aldicarb. The formation of aldicarb nitrile from aldicarb in environmental samples has been suspected (14) although only the oxidized forms of the nitrile have been detected in aerobic systems. It has been found that from 3 to 12% of the aldicarb applied degrades to either 2-methyl-2-(methylsulfinyl)propanenitrile or 2-mesyl-2methylpropanenitrile in potatoes (10%) (15),soils (5%) (16)) sugar beets (5%) (141, and aqueous cultures of soil fungi (3 to 11% depending on type of soil fungus) (17).
EXPERIMENTAL SECTION Apparatus. A Finnigan gas chromatograph/triple-stage quadrupole mass spectrometer/data system was used in this study. Electron energies of 70 and 100 eV were used for electron ionization (EI)and chemical ionization (CI),respectively. The chemical ionization reagent gas was methane or isobutane at an ionizer pressure of 107 Pa. The mass spectrometer was tuned with FC43 (perfluorotributylamine). The E1 spectra for aldicarb and aldicarb oxime were similar to those in the NBS library. Nitrogen collision gas was introduced at 0.23 Pa and collision energies were 10-20 eV for collisionally activated dissociation (CAD) spectra. The continuous dynode electron multiplier was operated at 850-900 V with the conversion dynodes at &3000 V. The gain was set for A/V. Selected ion monitoring for the 0 1984 American Chemical Soclety
