Rapid Screening Procedure for Pesticides and Polychlorinated Biphenyls in Fish: Collaborative Study

A simplified rapid method is presented to determine organochlorine pesticides and polychlorinated biphenyls in fish. Samples are mixed with sodium sulfate and blended with petroleum ether. A portion of the blend is placed on a miniaturized Florisil column and compounds are eluted with mixtures containing 6 and 15% ethyl ether in petroleum ether. Gas-liquid chromatography with electron capture detection comparable to the official methods (29.018) is used for determination of residues. Each of 7 collaborators reported results in duplicate for 10 samples containing one or more of the following compounds: p,p’-DDD,p,p’-DDE, p,p’-DDT, dieldrin, heptachlor epoxide, Aroclor 1254, and Aroclor 1260. Recoveries ranged from 79.3 to 100.7%. The coefficients of variation between laboratories ranged from 6.3 to 20.6%. This method allows up to 80% reduction in reagents and up to 50% reduction in analytical time, and requires less laboratory space than current official methods. The method has been adopted official first action.

Multiresidue Gas Chromatographic Method for Determining Synthetic Pyrethroid Pesticides in Agricultural Products: Collaborative Study

Fourteen laboratories from 6 countries and regions participated in an international collaborative study to evaluate a multiresidue gas chromatographic (GC) method for determining 8 synthetic pyrethroid pesticides in grains, fruits, and vegetables. The study design was based on Youden’s matched-pairs principle for collaborative tests of analytical methods. Each laboratory analyzed 12 collaborative samples of wheat, oranges, and tomatoes as blind samples. Wheat samples were extracted with acetonitrile–water (2 + 1), while orange and tomato samples were extracted with acetone. Residues were partitioned into hexane, evaporated to dryness with a rotary evaporator, and then dissolved in hexane. The hexane extract was partitioned with acetonitrile and cleaned up on a 5% water-deactivated Florisil column with 6% ethyl ether in hexane as eluant. Residue concentrations were determined by GC with electron capture detection with split-less injection by comparison with single-point calibration standards. The appropriate standard concentration was determined by screening sample extracts before analysis. The multiresidue method was tested over the concentration range of 0.0951.909 mg/kg depending on the 8 different of pesticides and agricultural products analyzed in the collaborative study. Statistical analysis of data from 13 laboratories showed weighted average recoveries for 8 pyrethroids in wheat, oranges, and tomatoes at 0.105–1.909,0.095–1.909, and 0.105–0.954 mg/kg, respectively, ranging from 91.8 to 100.2%, from 88.1 to 100.6%, and from 88.2 to 101.5%, respectively. Reproducibility relative standard deviation values ranged from 6.46 to 17.74%, from 5.94 to 18.13%, and from 5.59 to 10.48%, respectively. Repeatability relative standard deviation values ranged from 6.34 to 10.84%, from 5.19 to 11.72%, and from 3.20 to 8.09%, respectively. The multiresidue GC method for determining synthetic pyrethroid pesticides in agricultural products has been adopted first action by AOAC INTERNATIONAL.

Multiresidue method for the chromatographic determination of triazine herbicides and their metabolites in raw agricultural products

A method is described for the determination of 19 triazine herbicides and 4 metabolites in 6 agricultural products that represent diverse matrixes. In addition, a modification of this method to determine the more water-soluble metabolite, desethyldesisopropylatrazine, is described. In both these procedures, residues are extracted with methanol, and the product coextractives are removed using solvent partition and cation-exchange solid-phase extraction chromatography. A nitrogen phosphorus detector and DB-17 megabore column are used for the temperature-programmed chromatographic determination of samples fortified at 0.02-1.0 ppm levels. Average recoveries ranged from 81.1 to 106.2% for the parent herbicides and from 59.6 to 87.5% for the metabolites on all crops. An average recovery of 101.1% was obtained for desethyldesisopropylatrazine.

Gas Chromatographic Method for Ethylene Dibromide in Grains and Grain-Based Products: Collaborative Study

Nine laboratories analyzed samples of whole grain, intermediate, and ready-to-eat products for ethylene dibromide (EDB) residues. Supplied samples of wheat, rice, and flour contained both fortified and incurred EDB; corn bread mix, baby cereal, and bread contained only fortified EDB. The whole grains and intermediates were analyzed by the same basic procedural steps as in the official method for multifumigants: They were extracted by soaking in acetone-water (5 + 1). The baby cereal and bread were analyzed by a modification of the Rains and Holder hexane co-distillation procedure. EDB was determined by electron capture gas chromatography operated with an SP-1000 column. All products contained 3 different levels of EDB and were analyzed as blind duplicates. Overall mean recoveries ranged from 85.2% for 69.6 ppb to 105.0% for 4.35 ppb, both in baby cereal. Interlaboratory relative standard deviations ranged from 5.7% for 869 ppb in wheat to 20.2% for 69.6 ppb in baby cereal, both fortified. Mean levels of incurred EDB in wheat, rice, and flour were 926.7, 982.0, and 49.9 ppb, respectively; corresponding relative standard deviations were 9.9, 7.7, and 13.1%. The method was adopted official first action.