Anal. Chem. 1998, 70, 3329-3332
Extraction of Aldicarb and Its Metabolites from Excreta and Gastrointestinal Tissue Frances D. Harper
The Department of Environmental Toxicology, Clemson University, Pendleton, South Carolina 29670 Carol P. Weisskopf
Washington State University, Richland, Richland, Washington 99352 George P. Cobb*
The Institute of Environmental and Human Health, Texas Tech University, Lubbock, Texas 79416
Carbamate insecticide screens often include aldicarb and its oxidative metabolites, aldicarb sulfoxide (ASX), and aldicarb sulfone (ASN). The rapid hydrolysis and thermal cleavage of the C-N bond within the carbamate functional group of these compounds produces nitrile transformation products. Nitriles are primary transformation products from aldicarb, its sulfoxide, or its sulfone. However, these nitriles are infrequently monitored. The method reported used acetonitrile/water extraction and HPLC postcolumn derivitization to determine aldicarb, ASX, and ASN from avian excreta and from gastrointestinal (GI) tissue. Recoveries of aldicarb, ASX and ASN from excreta were of 79% ( 5.4, 120% ( 7.7, and 93% ( 6.2, respectively. Recoveries from tissue were 70% ( 5.0, 80% ( 12.1, and 85% ( 6.7, respectively. The same extraction procedure and a GC-FPD analysis were used to determine nitrile metabolites from the same tissues. Aldicarb nitrile, ASX nitrile, and ASN nitrile recoveries from excreta were 42% ( 2.3, 65% ( 3.6, and 79% (3.3, respectively. Overall recoveries from tissue were 29% ( 3.4, 72% (8.3, and 83% (11.4, respectively. Since aldicarb, ASX, and ASN are normally detectable in organ tissues for 1-2 days following exposure, determining the presence of nitrile cleavage products provides an important forensic tool for evaluating aldicarb exposures. Analytical methods for determination of the carbamate insecticide aldicarb [2-methyl-2-(methylthio)propionaldehyde O-(methylcarbamoyl)oxime] and its oxidative transformation products, aldicarb sulfoxide [2-methyl-2-(methylsulfinyl)propionaldehyde O-(methylcarbamoyl)oxime] and aldicarb sulfone [2-methyl-2(methylsulfonyl)propionaldehyde O-(methylcarbamoyl)oxime], are relatively well established in abiotic matrixes.1 HPLC-MS methods to quantify these compounds and their nitrile cleavage products, aldicarb nitrile [2-methyl-2-(methylthio)propanenitrile], aldicarb sulfoxide nitrile [2-methyl-2-(methylsulfinyl)propionitrile], (1) USEPA. Method 531; EPA-600/4-85/054; United States Environmental Protection Agency: Washington, DC, 1985. S0003-2700(97)01268-7 CCC: $15.00 Published on Web 06/18/1998
© 1998 American Chemical Society
and aldicarb sulfone nitrile, [2-methyl-2-(methylsulfonyl)propionitrile], have been developed for water but for no other matrix.2 EPA method 531 may be used for a wide number of carbamates with a primary amine group,1 even though the postcolumn derivitization carbamates and their oxidative transformation products and the fluorescence quantum yield of the derivatives may be variable.2,3 The AOAC registered a difficult derivatization technique followed by packed-column gas chromatography (GC) for aldicarb and its transformation products. In this and other GC techniques, aldicarb is thermally labile and rapidly degrades on the injection port or on column. Traditionally, this process converts aldicarb to aldicarb nitrile when gas chromatography is used as the detection method.4 Since aldicarb nitrile (ANT) is a major hydrolysis product of aldicarb,5 its transformation on the gas chromatograph would cause concern. Significant transformation of aldicarb sulfoxide (ASX) and aldicarb sulfone (ASN) to nitriles during GC analyses poses similar analytical problems. ASX and ASN have been identified as transformation products that are indicative of aldicarb exposure.6-8 Therefore, aldicarb, ASX, and ASN are normally quantified during aldicarb exposure assessments. Unfortunately, these compounds are not stable in living or dead animals for more than 2 days. ANT formation has been documented in plant, insect,9,10 and soil studies.11 Nitriles have been identified as primary aldicarb metabolites in soils 28 (2) Miles, C. J.; Delfino, J. J. J. Chromatogr. 1984, 299, 275-280. (3) Miles C. J.; Moye, H. A. Anal. Chem. 1988, 60, 220-226. (4) Trehy, M. L.; Yost, R. A.; McCreary, J. J. Anal. Chem. 1984, 56;12811285. (5) Hicks, B. W.; Dorough, H. W.; Mehendale, H. M. J. Agric. Food Chem. 1972, 20, 151-156. (6) Cochrane, W. P.; Lanouette, M.; Trudeau, S. J. Chromatogr. 1982, 243 307-314. (7) Lian, D. X.; Yang, L.; Yun, W. X.; Hua, S.; Hu, C. J. Chromatogr. 1991, 542, 526-530. (8) Liu, C. H.; Mattern, G. C.; Yu, X.; Rosen, R. T.; Rosen, J. D. J. Agric. Food Chem. 1991, 39, 718-723. (9) Bull, D. L.; Linquist, D. A.; Coppedge, J. R. J. Agric. Food Chem. 1967, 15, 610-616. (10) Metcalf, R. L.; Fukuto, T. R.; Collins, C.; Borck, K.; Burk, J.; Reynolds, H. T.; Osman, M. F. J. Agric. Food Chem. 1966, 14, 579-584. (11) Lightfoot, E. N.; Thorn, P. S.; Jones, R. L.; Hansen, J. L.; Romine, R. R. Environ. Toxicol. Chem. 1987, 6; 377-394.
Analytical Chemistry, Vol. 70, No. 15, August 1, 1998 3329
days following treatment with aldicarb.12,13 Therefore, wildlife exposure to aldicarb could be more accurately assessed by determination of ANT, aldicarb sulfoxide nitrile (ASXNT), and aldicarb sulfone nitrile (ASNNT), along with the more traditionally measured aldicarb, ASX, and ASN. Such a procedure is essential given the instability of aldicarb, ASX, and ASN in animal tissues. Rapid degradation precludes forensic evaluation of many proported aldicarb exposures. Analysis of ANT, ASXNT, and ASNNT would extend the period in which aldicarb exposure could be determined in recovering, impaired, or dead subjects. Thus, we sought a method that allows analysis of aldicarb and its oxidative and hydrolytic transformation products in mammalian urine, avian excreta, and organ tissues from vertebrates.14 The extraction efficiencies of pertinent solvents and the stability of aldicarb and many of its metabolites in tissue were also examined. Solid-phase extraction (SPE) methods to extract aldicarb from water in the literature generally indicate fairly high detection limits (>1.3 µg/L) or low recoveries (
