718 Reprinted from JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY, 1991,39. Copyright@ 1991 by the American Chemical Society and reprinted by permission of the copyright owner. Multiresidue Determination of Nonvolatile and Thermally Labile -rX Pesticides in Fruits and Vegetables by Thermospray Liquid ~1 J Chromatography/Mass Spectrometry ,f''-f Meg.)" Chao-Hong Liu,t Gregory C. Mattern,: Xiaobing Yu,l Robert T. Rosen,n and Joseph D. Rosen• ,,,, Department of Food Science, Cook College, Rutgers University, New Brunswick, New Jersey 08903 A multiresidue method using high-performance liquid chromatographylthermospray IIDJJBS spectrometryI $elected ion monitoring (HPLCITSP IMSISIM) to determine 19 thermaHy labile 'fllld nonvolatile pesticides in frui and vegetables was evaluated. The pesticides were extracted from apples, beans, Jettuce, peppers, potatoes, and tomatoes with a slightly modified Luke multiresidue extraction procedure. Aldicarb, aldicarb sulfoxide, bufencarb, carboxin, chlorbromuron, diuron, linuron, methiocarb, meth­ omyl, metobromuron, monuron, neburon, oxamyl, propoxur, and thiodicarb were analyzed by mass spectrometry in the positive ion mode. Fenvalerate, folpet, iprodione, and oryzalin were analyzed in the negative ion mode. The limits of detection of the pesticides in the crops were in range 0.025-1 ppm. For those 14 pesticides with limits of detection of0.25 ppm and below, recovery studies were performed at the 0.5 ppm fortification level in each of the six crops. Recoveries were between 69 and 110%, except. for carboxin, which was recovered between 33 and 54%. Coefficients of variation were between 1.4 and 23.6%, with an average of 9.05 %. ' PROPERTY OF NERBY , NJ DEPT OF ENV. pA8T&Q. ~ .. INFORMATION RESOUflC! INTRODUCTION urea herbicides in fruits and vegetables by liquid chro­ matography with postcolumn photodegradation, chemical Several hundred pesticides are used in the United States derivatization, and spectrofluorometry was reported by on fruits and vegetables, and it is impossible to analyze Luchtefeld (1987). Both methods require cleanup steps for every registered pt\Sticide in a reasonable amount of including solvent partitioning and column chromatogra­ time. This is due, in part, to the myriad number ofseparate phy. analytical procedures that have been developed over the past several decades. The FDA official methods for the determination of car­ The Luke extraction procedure (Lukeetal.,1981;AOAC, boxin and oryzalin in crops are based on chemical de­ 1985), which can extract more than 230 pesticide residues rivatization followed by gas chromatography (FDA, 1985). (Luke et al., 1988) ranging from nonpolar pesticides (e.g., Carboxin is extracted from the crops by Soxhlet extraction DDT) to the highly polar ones (e.g., methamidofos), is the with methanol and partitioned into chloroform. Caustic procedure most widely used by the U.S. Food and Drug digestion after the evaporation of chloroform cleaves Administration (FDA). This method requires no cleanup aniline from carboxin, and the aniline is recovered by steam steps, relying for its specificity on a variety of specific GC distillation. Carboxin is then determined as aniline by detectors. Because ofthe._wide variety of pesticide classes, gas chromatography with a microcoulometric nitrogen several specific detectors would be required (each. one detector. Oryzalin, on the other hand, is extracted from requiring a separate GC determination) for a cop1plete. the crops by blending with methanol and derivatized to analysis. Mattern et al. (1990) have shown that it is a N ,N-dimethyl derivative with methyl iodide after possible to speed up these analyses by using chemical filtration. The N ,N-dimethyl derivative is purified by ionization GCIMS for detection and quantification. GC alumina column chromatography and finally determined systems, however, are not capable of determining thermally by electron capture gas chromatography. labile and nonvolatile pesticides, and the method of Mat­ High-performance liquid chromatography is very ef­ tern et al. is not applicable to such pesticides. fective in separating nonvolatile and thermally labile To analyze these pesticides, several more methods all compounds, but conventional detectors, such as ultraviolet different, have been developed. Krause (1985) develoi>ed absorption and flame ionization, are not sufficiently a liquid chromatographic multiresidue method using an selective to determine the target pesticides in complex in-line postcolumn fluorometric detector for the deter­ food matrices. A fluorescence detector could not be used mination of N-methylcarbamates in grapes and potatoes. in a multiresidue procedure because it would not detect A multiresidue method for the determination of phenyl- nonfluorescent pesticides. Bellar and Budde (1988) re­ ported the determination of nonvolatile organic com­ • Author to whom correspondence should be addressed. pounds in aqueous environmental samples using TSP LC I DEP t Present address: Department of Health, P.O. Box 91- MS. They concluded that among 52 pesticides and other 103, Taipei 10726, T-aiwan. compounds of environmental interest tested there were f Present address: Mobay Research Park, 177 45 S. Met­ 26 compounds for which precision, accuracy, and method TX calf Ave., Stilwell, KS 66085-9104. detection limits were adequate for environmental mon­ !571 §.~resent .address: Dep.artment of Applied Chemistry, itoring. .... BeiJmg Institute of Chemical Technology, Heping Street, In this study, an attempt was made to extend the work M8!S Beijing, People's Republic of China. of Bellar and Budde to the analysis of fruits and vegetables U~t1 U Permanent address: Center for Advanced Food Tech­ and to develop methodology that would combine the c.l nology, P.O. Box 231, Rutgers University, New Brunswick, analyses of phenylureas, carbamates, and several other NJ 08903. · pesticides into a single procedure. Determination of Pesticides in Produce J. Agric. Food Chern., Vol. 39, No. 4, 1991 719 EXPERIMENTAL PROCEDURES Table I. Ions Observed in the Positive Ion Mode Thermos pray LC/MS Spectra of Pesticides Tested Chemicals. Chlorbromuron, diuron, fenvalerate, folpet, ip­ pesticide MW base peak second ion rodione, linuron, methomyl, monuron, neburon, oryzalin, and oxamyl reference standards were purchased from Chern Service, aldicarb 190 157 208 (40)• Inc. (West Chester, PA). 2-Fluoro-9-fluorenone was purchased aldicarb sulfoxide 206 207 173 (24) from Aldrich Chemical Co. (Milwaukee, WI). Aldicarb, aldicarb bufencarb 221 222 sulfoxide, bufencarb, carboxin, methiocarb, metobromuron, carboxin 235 236 propoxur, and thiodicarb were supplied by the EPA (Research chlorbromuron 292 295 293 (75) Triangle Park, NC). Sodium chloride, ammonium acetate, diuron 232 233 235 (66) anhydrous sodium sulfate, and high-purity HPLC grade acetone, linuron 248 249 251 (66) 169 (13) acetonitrile, methanol, petroleum ether, and water were pur­ methiocarb 225 226 methomyl 162 163 chased from Fisher Scientific (Springfield, NJ). metobromuron 258 259 261 (98) Samples. The fruits and vegetables used for this study were monuron 198 199 collected from New Jersey supermarket distributors and various neburon 274 275 277 (66) farms in that state. The samples used for recovery and sensitivity oxamyl 2..19 163 • 237 (21) studies were previously determined to be free of the pesticides propoxur '209 210 227 (25) in this study by unspiked crops under the conditions specified thiodicarb 354 163 355 (54) below. • Percent abundance relative to base peak. Instrumentation Conditions. A Kratos Spectraflow 400 liquid chromatograph (Kratos, Ramsey, NJ) interfaced to a Vestee Model 201 thermospray LC/MS (Vestee Corp., Houston, TX) The sodium sulfate was washed with an additional50-mL portion and controlled by a Teknivent Vector/One data system of methylene chloride. A Snyder column was attached to the (Teknivent Corp., St. Louis, MO) on a Compac Deskpro 286 concentrator, and the solvent was evaporated to about 4 mL on personal computer was used. A 22 em X 4.6 mm i.d. Spheri-5 a steam bath. The appropriate internal standard stock solution reversed-phase C-18 HPLC column (Brownlee Labs, Santa Clara, (40 ILL) was added to the final concentrate, and the volume was CA) with a particle size of 51Lm was used. The mass spectrometer adjusted to 4 mL. was operated in either the positive ion or negative ion discharge Preparation of Calibration Curves. Individual solutions mode. The vaporizer tip temperature was held between 225 and of each pesticide at 250 ng/ ILL were prepared in methanol (except 235 °C, the scan time was 0.5 s, and the sweep width was 0.1 amu aldicarb sulfoxide in acetonitrile and folpet in acetone). A stock for both full-scan and selected ion monitoring (SIM) operations. solution of 50 ng/ ILL was prepared by mixing 1 mL from each For the determinations of aldicarb, bufencarb, carboxin, chlor­ individual solution and concentrating to 5 mL. The stock solution bromuron, diuron, linuron, methiocarb, methomyl, metobromu­ was serially diluted, and the appropriate amount of internal ron, monuron, neburon, propoxur, oxamyl, and thiodicarb the standard stock solution (1000 ng/ ~L) was added. The standard initial mobile phase composition was 20% acetonitrile, 65 <;;;, water, solutions then contained 1, 2, 5, 10, and 20 ng/ ILL of each pesticide and 15";, 0.013 M ammonium acetate solution. This was and 10 ng/ ILL of 2-fluoro-9-fluorenone internal standard. These programmed linearly to sor, acetonitrile, 5':'(; water, and 15<'(