ARTICLES. Federal Center for Animal Health (VNIIZZh), Yur evets, Vladimir, Russia b

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1 ISSN , Journal of Analytical Chemistry, 013, Vol. 68, No. 10, pp Pleiades Publishing, Ltd., 013. Original Russian Text V.G. Amelin, D.K. Lavrukhin, A.V. Tret yakov, 013, published in Zhurnal Analiticheskoi Khimii, 013, Vol. 68, No. 10, pp ARTICLES Combination of the Quick, Easy, Cheap, Effective, Rugged, and Safe (QuEChERS) Method and Dispersive Liquid Liquid Microextraction in the Identification and Determination of Pesticides from Various Classes in Food Products by Gas Liquid Chromatography V. G. Amelin a, b, D. K. Lavrukhin a, b, and A. V. Tret yakov b a Federal Center for Animal Health (VNIIZZh), Yur evets, Vladimir, Russia b Vladimir State University, ul. Gor kogo 87, Vladimir, Russia Received December, 011; in final form, December 5, 01 Abstract A procedure for the identification (104 substances) and determination (40 substances) of the active components of combined pesticides from different classes in water, vegetables, fruits, and meat by gas chromatography with mass-spectrometric and electron-capture detectors was proposed. The pesticides were extracted from the samples of vegetables, fruits, and meat with acetonitrile using the QuEChERS method. The extracts were preconcentrated by a factor of and additionally purified by dispersive liquid liquid microextraction. The pesticides were extracted from water by dispersive liquid liquid microextraction with hexane (degree of concentration was higher than 100). The limits of detection by the time-of-flight detector equaled mg/kg for solid samples and 1 μg/l for aqueous solutions. The limits of quantitation for pesticides were 1 mg/kg for solid samples and 0.05 μg/l for solutions. The analysis time was 1 h, and the RSD of the results did not exceed 18%. Keywords: pesticides; gas liquid chromatography; electron-capture detector; time-of-flight mass-spectrometric detector; water, vegetable, fruit, and meat analysis; QuEChERS method; dispersive liquid liquid microextraction DOI: 1134/S Along with the use of individual pesticides, the mixtures of pesticides from different classes are commonly used in the agriculture. Combined preparations, such as Eforia (λ-cyhalothrin and thiamethoxam), Engeo 47 SC, Borey (imidacloprid and λ-cyhalothrin), Nurell-D (chlorpyrifos and cypermethrin), Dospekh 3 (tebuconazole and imazalil), Titul duo (tebuconazole and propiconazole), Alto (cyproconazole and propiconazole), and Lyufoks (lufenuron and fenoxycarb), are well known [1, ]. Chromatography mass spectrometry [3 5], HPLC [6 9], voltammetry [10], enzyme immunoassay [11, 1], capillary electrophoresis [13 17], and gas chromatography [18, 19] are used for the monitoring of pesticide residues in food, agricultural products, and environmental samples. Procedures for the determination of individual pesticides or pesticides of the same class were proposed in the cited publications; however, the mutual effects of pesticides occurring in combination were not studied. The main problem in the determination of pesticides consists in their extraction from the test material, the removal of coextracted compounds (fats, waxes, lipids, etc.) from the extract, and the preconcentration of the extract because almost all chromatographic methods are insufficiently sensitive. The Quick, Easy, Cheap, Effective, Rugged, and Safe (QuEChERS) method was proposed for the safe and rapid extraction of pesticides (primarily for fruits, vegetables, cereals, and honey) [0]. In this method, the extract is not preconcentrated; therefore, it is not applied to the determination of pesticides in products with low maximum permissible levels (MPLs). Chromatography mass spectrometry is a technique used for the subsequent analysis. However, the insufficient cleaning of the extract restricts the application of this sample preparation method to other chromatographic techniques. A unique preconcentration method dispersive liquid liquid microextraction (DLLME) was proposed in 006 for the determination of pesticides in 91

2 COMBINATION OF THE QUICK, EASY, CHEAP, EFFECTIVE, RUGGED, AND SAFE 913 water, juices, fruits, and tea [1 3]. This method makes it possible to reach high degrees of preconcentration and extraction of target components; however, it has limited applications to solid test materials. In this work, we evaluated the possibility of combining sample preparation according to the QuEChERS method and extract preconcentration (refining) by DLLME for the identification and determination of pesticides from different classes that simultaneously occurred in water, vegetables, fruits, meat, and other food products using gas liquid chromatography with mass-spectrometric and electron-capture detectors. EXPERIMENTAL Instrumentation. Chromatography mass-spectrometric analysis was carried out on a Micromass GCT Premier ТМ ToF MS system (Waters, Great Britain), which included an Agilent 6890N gas chromatograph, a time-of-flight mass-spectrometric detector with a resolution of 9300 for hexachlorobenzene (m/z ), and a data processing system based on an of IBM PC-AT personal computer. Separation was performed on a quartz capillary column 30 m in length with an inside diameter of 0.3 mm (DB-5ms stationary phase film thickness of 0.5 µm). The column temperature was С (heating rate, 15 K/min), and the injector temperature was 40 С. Helium was a carrier gas; the carrier-gas inlet pressure and flow rate were MPa and 1 ml/min, respectively. A 1-µL sample was injected into the chromatograph in the splitless mode using a CTC CombiPal autosampler. The mass spectra were measured using 70-eV electron ionization; the rate of scanning was 0.09 s, the range of scanning was m/z, and the determination error was 0.65 mda. A Clarus-600 gas chromatograph with an electroncapture detector (ECD) (Perkin-Elmer, the United States) was used. Separation was performed on an Rtx-Pesticides quartz capillary column (Merck, Germany) 30 m in length with an inside diameter of 0.3 mm (stationary phase film thickness of 0.5 µm). The column temperature was С (heating rate, 15 K/min), the injector temperature was 40 С, and the detector temperature was 300 С. Nitrogen was a carrier gas, and its flow rate was ml/min. A 1-µL sample was injected into the chromatograph in the splitless mode using an autosampler. Reagents. The following standard reference samples of individual pesticides ( % purity) were used: simazine (GSO ), atrazine (GSO ), linuron (GSO ), malathion (IPO 460), chlorpyrifos (GSO ), bentazon (IPO 050), imidacloprid (IPO 97), acetamiprid (No. C , Dr. Ehrenstorfer), metsulfuron methyl (GSO ), propiconazole (IPO 581), tebuconazole (GSO ), thiabendazole (RM, No ), thiamethoxam (RM, No. 3794), propazin (GSO ), promethrine (GSO ), desmetryn (GSO ), terbutylazine (SOP 0-05), terbutryn (SOP 1-05), metribuzin (GSO ), metazachlor (IPO 471), metolachlor (SOP 39-06), bensulfuron methyl (SOP 60-06), sulfometuron methyl (SOP 55-06), tribenuron methyl (GSO ), diuron (GSO ), fluometuron (GSO ), chlorbromuron (SOP 4-05), amidosulfuron (SOP 31-06), chlortoluron (GSO ), metoxuron (SOP 16-05), triasulfuron (SOP 46-06), penkonazole (GSO ), flutriafol (SOP 41-06), cyproconazole (GSO ), triticonazole (SOP 67-06), triadimefon (GSO ), epoxiconazole (GSO ), diniconazole (GSO ), diphenoconazole (GSO ), imazalil (SOP 40-06), prochloraz (GSO ), thiabendazole (GSO ), carbofuran (GSO ), fenoxycarb (SOP -05), carbosulfan (SOP 4-06), dimethoate (IPO 146), fozalon (GSO ), parathion methyl (MSO ), pirimiphos-methyl (No , Dr. Ehrenstorfer), diazinon (IPO 18), hymexazol (SOP 13-05), vinclozolin (SOP 5-05), and carbaryl (GSO ). Pesticide mixture Nos. 34, 36, 40, 44, 51, 118, 18, 19, 3, and 35 (Dr. Ehrenstorfer) were also used. Solutions with a concentration of 100 µg/ml were prepared by the dissolution of the corresponding weighed portions in hexane or acetonitrile. Working solutions were prepared by diluting the stock solutions with acetonitrile or hexane the day they were used. Acetonitrile, hexane for chromatography, tetrachloromethane, bromobenzene, and dichloromethane (Merck, Germany); chemically pure MgSO 4 ; chemically pure NaCl; chemically pure sodium citrate tribasic dihydrate; chemically pure sodium citrate dibasic sesquihydrate; and the sorbents Bondesil-PSA and С 18 (Varian, the United States) were used. Sample preparation. The extraction of pesticides from solid samples and the purification of extracts were accomplished using the QuEChERS method. A ground sample of 10 g was placed in a 50-mL centrifuge tube, and 10.0 ml of acetonitrile was added; the tube was stoppered, and the contents were vigorously stirred for 1 min. Then, 4.0 g of anhydrous MgSO 4, 1.0 g of NaCl, 1.0 g of sodium citrate tribasic dihydrate, and 0.5 g of sodium citrate dibasic sesquihydrate were introduced. After the introduction of the salts, the contents were stirred for 1 min and centrifuged at 3000 rpm for 5 min; an 8-mL portion of the upper part JOURNAL OF ANALYTICAL CHEMISTRY Vol. 68 No

3 914 AMELIN et al α-hcch β-hcch γ-hcch, 4-DDE 4, 4-DDE Fig. 1. Mass chromatograms of substances with the same fragment masses. of the extract was taken and transferred to a 15-mL centrifuge tube, which contained a mixture of MgSO 4 (0.5 g) and the Bondesil-PSA sorbent (0.5 g) for vegetables and fruits or the С 18 sorbent (0.5 g) for meat. The tube was vigorously stirred for 30 s and centrifuged at 3000 rpm for 5 min. In the first version, 4 ml of the extract was taken and evaporated to dryness on a rotary evaporator at a temperature of 40 С. The dry residue was dissolved in 0.4 ml of hexane, and the solution was chromatographed. In the second version, 4 ml of the extract was placed in a centrifuge tube and diluted with water to 10 ml; 1 ml of acetone containing 100 µl of hexane or chloroform was introduced using a syringe. The resulting emulsion was centrifuged at 3000 rpm for 5 min. The upper layer of hexane (80 ± 3 µl) or chloroform (40 ± 1 µl) was taken, placed in a microvial, and chromatographed. Pesticides were extracted from water using DLLME by the addition of 1 ml of ethanol containing 100 µl of hexane (50 µl of chloroform) to 10 ml of water. The resulting emulsion was centrifuged at 3000 rpm for 5 min. The upper layer of hexane (80 ± trans-nonachlor Endosulfan Pyrene Chlordane m/z Fig.. Mass spectrum of pyrene, α-chlordane, α-endosulfan, and trans-nonachlor at a retention time of min. JOURNAL OF ANALYTICAL CHEMISTRY Vol. 68 No

4 COMBINATION OF THE QUICK, EASY, CHEAP, EFFECTIVE, RUGGED, AND SAFE 915 Table 1. Pesticides identified by gas chromatography mass spectrometry (time-of-flight mass-spectrometric detector) Pesticide t R, min Characteristic ions, m/z ion ion 1 ion JOURNAL OF ANALYTICAL CHEMISTRY Vol. 68 No Recovery*, % Chemical class Chlortoluron (79) Phenylureas Dichlorvos (87) OPP** Carbofuran phenol (94) Carbaminates Metribuzin (75) sym-triazines Carbaryl (85) Carbaminates Nifos (89) OCP Propachlor (9) OCP*** DNOC (86),6-Dinitro-o-cresol,4-D methyl ester (93) Arylhydroxyalkyl carboxylic Dicamba (77) Benzoic acid derivatives Trifluralin (88) Dinitroanilines,4-D ethyl ester (90) Arylhydroxyalkyl carboxylic α-hcch (90) OCP Hexachlorobenzene (98) OCP,4-D isopropyl ester (83) Arylhydroxyalkyl carboxylic Dimethoate (88) OPP Carbofuran (70) Carbaminates Simazine (76) sym-triazines Atrazine (76) sym-triazines Propazine (73) sym-triazines β-hcch (88) OCP Clomazone (70) Isoxyzolidinones Dimethipin (69) Pentachloronitrobenzene (93) OCP γ-hcch (93) OCP Terbuthylazine (73) Triazines Diazinon (70) OPP,4-D propyl ester (70) Arylhydroxyalkyl carboxylic Chlorothalonil (80) OCP,4-D isobutyl ester (80) Arylhydroxyalkyl carboxylic Vinclozolin (89) Dinitroanilines Desmatryn (77) sym-triazines Dimethenamid (69) Amides Metribuzin (77) sym-triazines,4-d butyl ester (80) Arylhydroxyalkyl carboxylic Metalaxyl (81) Alanine derivatives Carbaryl (85) Carbaminates Prometryn (78) sym-triazines Heptachlor (90) OCP Terbutryn (74) sym-triazines Pirimiphos-methyl (87) OPP Ethofumesate (86) Benzofurans Linuron (77) Phenylureas Malathion (90) OPP Dichlofluanid (70) Sulfinamides Chlorpyrifos (98) OPP Triadimefon (70) OPP Aldrin (90) OCP Chlorthal-dimethyl (76) OCP Bentazone (90) Thiadiazines

5 916 AMELIN et al. Table 1. (Contd.) t R, min Characteristic ions, m/z Recovery*, % Pesticide ion ion 1 ion Chemical class Pendimethalin (78) Phenylamines Metazachlor (75) Phenylamines Penconazole (79) Triazoles Isophen (70) OPP Heptachlor epoxide (89) OCP Procymidone (73) Dicarboxylic acid imides Triadimenol (76) Triazoles Captan (97) Phthalimines γ-chlordane (98) OCP Fluometuron (71) Phenylureas,4-DDE (85) OCP α-chlordane (93) OCP α-endosulfan (86) OCP trans-nonachlor (85) OCP Imazalil (77) Imidazoles Oxadiazon (75) Oxadiazones Oxyfluorfen (73) Diphenyl ethers 4,4-DDE (93) OCP Buprofezin (97) Thiadiazines,4-D ethylhexyl ester (88) Arylhydroxyalkyl carboxylic,4-ddd (78) OCP Dieldrin (90) OCP Nitrofen (77) Phenyl ethers Endrin (88) OCP β-endosulfan (89) OCP Fluazinam (80) Pyrimidine amines 4,4-DDD (93) OCP,4-DDT (90) OCP Propiconazole (77) Triazoles Propiconazole (81) Triazoles 4,4-DDT (90) OCP,4-Methoxychlor (80) OCP Dichlorofop-methyl (87) Arylhydroxyphenoxy propionates Bifenthrin (99) Pyrethroids Fenoxycarb (88) Carbaminates Bromopropylate (78) Benzylates 4,4-Methoxychlor (80) OCP Phosalone (79) OPP Amitraz (70) Amidines γ-cyhalothrin (106) Pyrethroids Mirex (96) OCP Fenoxaprop-P-ethyl (80) OPP cis-permethrin (87) Pyrethroids trans-permethrin (87) Pyrethroids Pyridaben (70) Pyridazinones Prochloraz (75) Azoles β-cyfluthrin (103) Pyrethroids α-cypermethrin (89) Pyrethroids β- Cypermethrin (89) Pyrethroids Fluvalinate (91) Pyrethroids Esfenvalerate (103) Pyrethroids Difenoconazole (88) Triazoles Difenoconazole (88) Triazoles Deltamethrin (99) Pyrethroids Notes: * The recovery of pesticides (0.05 mg/l or mg/kg) from 10 ml of water using DLLME with hexane and (in parentheses) from 10 ml of an aqueous solution containing 4 ml of an acetonitrile extract from grapes using the QuEChERS method. ** OPP refers to organophosphorus pesticides. *** OCP refers to organochlorine pesticides. JOURNAL OF ANALYTICAL CHEMISTRY Vol. 68 No

6 COMBINATION OF THE QUICK, EASY, CHEAP, EFFECTIVE, RUGGED, AND SAFE 917 Table. Pesticide recovery with the use of DLLME (matrix: water of a meat extract obtained in accordance with the QuEChERS method) Recovery, % Pesticide chloroform (50 40 μl) hexane ( μl) dichloromethane (00 30 μl) bromobenzene (30 0 μl) tetrachloromethane (50 40 μl) Chlorpyrifos 98 ± ± 3 65 ± 4 30 ± 6 63 ± 4 Bifenthrin 99 ± 110 ± 8 66 ± 5 54 ± 7 58 ± 5 λ-cyhalothrin 87 ± 3 9 ± 5 56 ± 4 65 ± 4 65 ± 4 Cypermethrin 97 ± 3 99 ± 4 58 ± 5 30 ± 3 37 ± 6 Fluvalinate 105 ± 1 88 ± 67 ± 8 7 ± 45 ± 7 Note: Extractant added and the resulting phase volumes, respectively. (а) (b) Fig. 3. Chromatograms of extracts from grape prepared by the QuEChERS method (a) with extract evaporation in accordance with the first version and (b) in combination with DLLME (extractant: hexane). JOURNAL OF ANALYTICAL CHEMISTRY Vol. 68 No

7 918 AMELIN et al. (а) (b) (c) Fig. 4. Chromatograms of microextracts from grape prepared with the use of (a) hexane, (b) chloroform, (c) bromobenzene, (d) dichloromethane, (e) tetrachloromethane, and (f) a standard mixture: (1) chlorpyrifos, () bifenthrin, (3) λ-cyhalothrin, (4)cypermethrin, and (5) fluvalinate. JOURNAL OF ANALYTICAL CHEMISTRY Vol. 68 No

8 COMBINATION OF THE QUICK, EASY, CHEAP, EFFECTIVE, RUGGED, AND SAFE 919 (d) (e) (f) Fig. 4. Contd. JOURNAL OF ANALYTICAL CHEMISTRY Vol. 68 No

9 90 AMELIN et al. Table 3. Pesticides determined by GC-ECD, calibration equations, and analytical ranges Pesticide t R, min Analytical range, mg/l Calibration equation R Linuron Y = 167x 37x Dichlorvos Y = 558x + 674x Chlorbromuron Y = x 47x Hexachlorobenzene Y = x α-hcch Y = 54694x Propachlor Y = 1x + 64x γ-hcch Y = 5465x β-hcch Y = 38550x Diazinon Y = 153x 73x Heptachlor Y = 51993x Dimethoate Y = 41895x Aldrin Y = 6516x Chlorothalonil Y = 16914x Chlorpyrifos Y = 1953x 333x Vinclozolin Y = 736x 518x Malathion Y = 13057x Dichlofluanid Y = 19x 689x ,4-DDE Y = 57781x Triadimefon Y = ( )x + ( )x ,4-DDE Y = x Penconazole Y = 9188x + 3x Thiamethoxam Y = 1x + 83x Captan Y = 538x + 135x ,4-DDD Y = 48790x Dieldrin Y = 575x ,4-DDT Y = 15813x Endrin Y = 4961x ,4-DDD Y = 5983x Imazalil Y = 39685x β-endosulfan Y = 55853x ,4-DDT Y = 9366x Propiconazole Y = 10197x Propiconazole Y = 18701x Bifenthrin Y = 58x + 15x Chloridazon Y = 39073x Phosalone Y = 35x + 364x γ-cyhalothrin Y = 8403x Cypermethrin Y = 7880x Esfenvalerate Y = 47x + 48x Fluvalinate Y = 1654x JOURNAL OF ANALYTICAL CHEMISTRY Vol. 68 No

10 COMBINATION OF THE QUICK, EASY, CHEAP, EFFECTIVE, RUGGED, AND SAFE 91 Table 4. Results of the analysis of food products (n = 3; P = 0.95) Test material Pesticide detectedl Found, mg/kg s r MPL*, mg/kg Banana Triadimefon Imazalil ± ± Canned corn Vinclozolin Triadimefon Thiamethoxam ± ± ± Peach Chlorpyrifos Vinclozolin Triadimefon Penconazole Thiamethoxam ± ± ± ± ± Strawberry Chlorbromuron Chlorpyrifos Thiamethoxam Vinclozolin Triadimefon Penconazole ± ± ± ± ± ± Not allowed Not allowed Cabbage Chlorpyrifos 0.81 ± Natural water Hexachlorobenzene α-hcch,4-ddt 4,4-DDE Atrazin ± * Maximum permissible levels of pesticide residues in the fresh food products of plant origin regulated by Russian legislation in accordance with GN (with addenda 1 9). JOURNAL OF ANALYTICAL CHEMISTRY Vol. 68 No

11 9 AMELIN et al. Table 5. Pesticide recoveries and the results of the determination of pesticides in meat (n = 3; P = 0.95). The recovery was determined upon the addition of 0.05 mg/kg of pesticide Pesticide found, mg/kg Meat beef pork chicken recovery, % found, mg/kg recovery, % found, mg/kg recovery, % Linuron Dichlorvos Chlorbromuron Propachlor Diazinon Chlorothalonil Chlorpyrifos 0.01 ± ± ± Vinclozolin Malathion Dichlofluanid Triadimefon 0. ± ± ± Penconazole Thiamethoxam Captan Imazalil Diniconazole Propiconazole Bifenthrin Chloridazon Phosalone λ-cyhalothrin Fluvalinate α-cypermethrin β-cypermethrin 0.53 ± ± Esfenvalerate *Not detected. µl or 40 ± 1 µl of chloroform) was taken, placed in a microvial, and chromatographed. RESULTS AND DISCUSSION Identification of pesticides. Polar pesticides are well separated on a capillary column with the stationary phase DB-5ms and determined using a time-of-flight mass-spectrometric detector. The isomers of synthetic pyrethroids, propiconazole, diphenoconazole, carbaryl, HCCH, DDE, and DDT have the same masses of characteristic ions but different retention times (Table 1, Fig. 1). Figure shows the mass-spectra of α-chlordane, α-endosulfan and trans-nonachlor, which form a single peak (15.58 min) in the total ion current chromatogram. The use of the ChromaLynx ТМ software makes it possible to identify these compounds in the selective ion monitoring mode. The limits of detection were mg/l for 104 pesticides; therefore, for the identification of pesticides with consideration for their MPLs in the analyzed materials, the extracts from solid test materials obtained according to the QuEChERS method were preconcentrated by a factor of 50, and water was preconcentrated by a factor of with the use of DLLME. As an example, Table 1 summarizes the recoveries of pesticides from water and the extracts from grapes; these values are higher than 70%. Optimization of DLLME conditions. Chloroform, dichloromethane, tetrachloromethane, bromoben- JOURNAL OF ANALYTICAL CHEMISTRY Vol. 68 No

12 COMBINATION OF THE QUICK, EASY, CHEAP, EFFECTIVE, RUGGED, AND SAFE 93 zene, and hexane were used as extractants for DLLME, and ethanol, acetone, and methanol were used as dispersants. Hexane and chloroform dissolved in ethanol were the best systems because cleaner extracts were obtained with their use, and the degree of pesticide extraction was higher than 80% (Table and Figs. 3, 4). In this case, chlorpyrifos and synthetic pyrethroids were chosen as model pesticides because they are commonly used. Determination of pesticides by GC-ECD. The majority of pesticides contain chlorine, chlorine and fluorine, chlorine and bromine, or sulfur atoms as constituents; therefore, an ECD, which is more sensitive, was used for quantitative analysis. All of the pyrethroids other than deltamethrin and bifenthrin are the mixtures of isomers, and they appear in chromatograms as two (cyhalothrin, cyfluthrin, permethrin), three (esfenvalerate) and four (cypermethrin) peaks. The limits of detection of pesticides (signal/noise ratio = 3) were 0.05 mg/kg; therefore, a preconcentration factor of 10 is sufficient for their determination in vegetables, fruits, and meat (Table 3). We developed a procedure for the quantitative determination of 40 pesticides in water, vegetables, fruits, and meat in the concentration range of µg/kg or µg/l for water (Tables 4, 5). We found that the concentrations of pesticide residues were higher than the MPLs of imazalil, triadimefon, thiamethoxam, penconazole, and vinclozolin in vegetables and fruits and of chlorpyrifos, cypermethrin, and triadimefon in beef and chicken meat. The duration of analysis was 1 h, and the relative standard deviation of the results of analysis was no higher than 18%. REFERENCES 1. Mel nikov, N.N., Novozhilov, P.K., Belan, S.R., and Pylova, T.N., Spravochnik po pestitsidam (Handbook of Pesticides), Moscow: Khimiya, Mel nikov, N.N., Pestitsidy. Khimiya, tekhnologiya i primenenie (Pesticides: Chemistry, Technology, and Use), Moscow: Khimiya, Navalon, A., Gonzalez Casado, A., El-Khattabi, R., and Vilchez, J.L., Analyst, 1997, vol. 1, p Petrova, T.M., Smirnova, I.M., and Volgarev, S.A., Agrokhimiya, 006, no. 4, p Barinova, E.S., Brodskii, E.S., Koverzanova, E.V., and Usachev, S.V., Zh. Anal. Khim., 1995, vol. 50, no. 3, p Koverzanova, E.V., Barinova, E.S., and Brodskii, E.S., J. Anal. Chem., 1996, vol. 51, no. 4, p Guand-Guo, Y. and Rai, S.K., J. Environ. Sci. Health, Part B: Pestic., Food Contam., Agric. Wastes, 004, vol. 39, p Mandich, A.I., Lazich, S.D., Okresh, S.N., and Gaal, F.F., Zh. Anal. Khim., 005, vol. 60, no. 1, p Rancan, M., Sabatini, A.G., Achilli, G., and Galletti, G.C., Anal. Chim. Acta, 006, vol. 555, p Navalon, A., El-Khattabi, R., and Gonzalez Casado, A., Microchim. Acta, 1999, vol. 130, p Wanatabe, S., Ito, S., Kamata, Y., Omoda, N., Yamazaki, T., Munakata, H., Kaneko, T., and Yuasa, Y., Anal. Chim. Acta, 001, vol. 47, p Eiki, W., Heesoo, E., Koji, B., Tomohito, A., Yasuo, I., Shozo, E., and Masako, U., Anal. Chim. Acta, 004, vol. 51, p Carretero, A., Cruces-Blanco, C.,Perez Duran, S., and Fernandez Gutierrez, A., J. Chromatogr., A, 003, vol. 1003, p Dinelli, G., Bonetti, A., Catizone, P., and Galletti, G.C., J. Chromatogr., B, 1994, vol. 656, p Hinsman, P., Arce, L., Rios, A., and Valcarcel, M., J. Chromatogr., A, 000, vol. 866, p Bolygo, E. and Atreya, N.C., Fresenius J. Anal. Chem., 1991, vol. 339, p Ibrahim, W., Aini, W., Monjurul, AlamS.M., and Sulaiman, A., J. Teknologi, C 003, vol. 38, p Niewiadowska, A., Kiljanek, T., Semeniuk, S., and Zmudzki, J., Bull. Vet. Inst. Pulawy, 010, vol. 54, p You, J., Weston, D.P., and Lydy, M.J., Arch. Environ. Contam. Toxicol., 004, vol. 47, p Anastassiades, M., Stajnbaher, D., and Schenck, F.J., J. AOAC Int., 003, vol. 86, no., p Zang, X.H., Wu, Q.H., Zhang, M.Y., Xi, G.H., and Wang, Z., Chin. J. Anal. Chem., 009, vol. 37, p Asensio Ramos, M., Ravelo Perez, L.M., Gonzalez Curbelo, M.A., and Hemandez Borges, J., J. Chromatogr., A, 011, vol. 118, p Krylov, V.A., Krylov, A.V., Mosyagin, P.V., and Matkivskaya, Yu.O., J. Anal. Chem., 011, vol. 66, no. 4, p Translated by V. Makhlyarchuk JOURNAL OF ANALYTICAL CHEMISTRY Vol. 68 No