Determination of chlorinated pesticide residues in foods. II. Potassium permanganate oxidation for cleanup of some vegetable extracts.

A potassium permanganate-dilute sulfuric acid KMnO4/dilute H2SO4 oxidation procedure was developed to supplement Florisil cleanup of some vegetable extracts. Following sample preparation and Florisil cleanup, a reaction mixture of the n-hexane eluate from the Florisil cleanup, 4% KMnO4, and 40% H2SO4 (1 + 1 + 1) was shaken in a test tube 2 min at room temperature and then centrifuged. The n-hexane phase was washed with 2 mL 0.1N NaOH and analyzed by GLC. Twelve chlorinated pesticides were completely recovered in the n-hexane phase. Aldrin was not recovered because its extreme instability caused it to decompose even in neutral solutions. Chlorinated pesticide residues in onion, garlic, carrot, and radish root were easily analyzed by the application of this oxidation procedure.     

Determination of chlorinated pesticide residues in foods. I. Rapid screening method for chlorinated pesticides in milk.

A rapid analytical method for determining chlorinated pesticide residues in milk was developed. Thirteen pesticides were almost completely extracted. Ten mL samples of fortified milk were extracted 3 times with 20 mL portions of n-hexane as follows: (A) in the absence of water-soluble solvent; in the presence of (B) 1 mL acetonitrile; (C) 3 mL acetonitrile; (D) 5 mL acetonitrile; (E) 5 mL ethanol; (F) 5 mL acetonitrile and 1 mL ethanol. System F produced the highest pesticide recoveries but the lowest fat extraction, thus eliminating the necessity for liquid-liquid partitioning and minimizing Florisil column cleanup. Pesticide recoveries throughout the procedure were 94--103%. It was noticed, however, that the fat in high fat-containing raw milk is more readily extracted than that in commercial milk.     

Automated sample cleanup for pesticide multiresidue analysis. Part II--Design and evaluation of column chromatography module

An automated, continuous flow system is described for Florisil column chromatography of pesticide residues from food extracts. Evaluation of the system using 5 common organochlorine and organophosphorus pesticides in 2 crop matrices demonstrates essentially no difference in recovery or precision between automated and currently used manual analyses. The automated procedure uses only 20% of the solvents and adsorbents used in the manual procedure and is 3 times faster.     

Determination of phytosterols in butter samples by using capillary column gas chromatography

A positive bias in the gas chromatographic (GC) analysis of butter for beta-sitosterol was discovered when attempting to confirm values by gas chromatography/mass spectrometry (GC/MS). The source of the problem was traced to an interfering material that was not effectively separated by packed column GC. Because capillary columns are known to provide superior separation, they were substituted for packed columns in the assay, and instrument parameters were modified accordingly. A compound with a similar retention time, identified by GC/MS as lanosterol, was separated from beta-sitosterol by the capillary column. The capillary column technique was applied to over 300 butter samples. The results indicate that the method can accurately quantitate beta-sitosterol in butter with no known interferences. The limit of detection for this method is 1 mg/100 g. Recoveries at a level of 3 mg/100 g averaged 98% with a coefficient of variation of 3.45%.     

Determination of organochlorine and organophosphorus pesticide residues in eggs using a solid phase extraction cleanup

A multiresidue solid phase extraction (SPE) method for the isolation and subsequent gas chromatographic determination of nonpolar organochlorine and polar organophosphorus pesticide residues in eggs is described. The method uses an acetonitrile extraction followed by an SPE cleanup using graphitized carbon black and aminopropyl SPE columns. Organophosphorus pesticides are determined by gas chromatography with flame photometric detection. After further cleanup of the extract using Florisil SPE columns, organochlorine pesticides are determined by gas chromatography with electron capture detection. Studies were performed using eggs containing both fortified and incurred pesticide residues. The average recoveries were 86-108% for 8 fortified organochlorine pesticide residues and 61-149% for 28 fortified organophosphorus pesticide residues.     

Evaluation of an automated gel permeation cleanup and evaporation systems for determining pesticide residues in fatty samples

The AutoVap 600 system, used in conjunction with an automated gel permeation chromatography (GPC) instrument, automatically collects and evaporates the effluent from the GPC column, dissolves the residue in a fixed volume of desired solvent, and quantitatively transfers it to a sealed vial. This system was evaluated and found to automate efficiently the cleanup of butterfat for pesticide residue analysis. Quantitative recoveries were obtained for each of 4 pesticides fortified in butterfat and cleaned up through the system and for 12 pesticide standards in the absence of sample matrix collected through the system. After loading, the system operates unattended and will automatically prepare up to 23 individual fat samples for determination by gas chromatography without additional cleanup.     

Automated sample cleanup for pesticide multiresidue analysis. III. Evaluation of complete system for screening subtolerance residues in vegetables

An automated continuous flow sample cleanup system intended for rapid screening of foods for pesticide residues in fresh and processed vegetables has been developed. Recovery and precision data for 8 pesticides in each of 3 crops are compared for the automated and manual procedures. Average recovery for samples fortified with pesticides between 0.026 and 0.277 ppm was 98% for the automated system and 92% for the manual procedure. Average coefficient of variation was 6.6% for the automated system and 4.2% for the manual procedure. In another evaluation, the automated system gave an average recovery of 95% for 12 pesticides commonly found in imported foods; the manual procedure gave an average recovery of 91%. Thus, the results obtained so far indicate that the automated system for sample cleanup gives results comparable to those obtained by manual procedures.     

Gas chromatographic determination of electron capture sensitive volatile industrial chemical residues in foods, using AOAC pesticide multiresidue extraction and cleanup procedures

Electron capture (EC) gas chromatographic (GC) parameters have been developed for determining some of the more volatile industrial chemicals that can be determined by the AOAC multiresidue method for organochlorine and organophosphorus pesticides with modified GC operating conditions. Retention times relative to pentachlorobenzene are reported for 143 industrial chemicals, pesticides, and related compounds on OV-101 GC columns at 130 degrees C. Also reported for most of the compounds are recoveries from fortified samples carried through the AOAC extraction and cleanup procedures for fatty and/or nonfatty foods, Florisil elution characteristics, and GC relative retention times on mixed OV-101 + OV-210 columns at 130 degrees C. Our laboratory has used the modified EC/GC parameters with the AOAC multiresidue extraction/cleanup procedures to determine many volatile halogenated industrial chemical contaminants in foods, chiefly in samples of fresh-water fish. Other modifications of the AOAC method are described to improve the tentative identification and quantitative measurement of these volatile residues.     

Simultaneous determination of neonicotinoid insecticides in agricultural samples by solid-phase extraction cleanup and liquid chromatography equipped with diode-array detection

Effective sample pretreatment procedures based on solid-phase extraction (SPE) for multiresidue determination of seven neonicotinoid insecticides in agricultural products were investigated. After extraction with acetone and concentration, the insecticides in aqueous sample extracts were transferred into organic solvent phases with a Chem Elut SPE cartridge. Finally, the eluate from the cartridge was cleaned up with a SPE cartridge packed with graphitized carbon black and aminopropyl silica gel, which showed a higher cleanup efficiency than the classical silica gel SPE cartridge. Seven insecticides were separated on a reversed-phase C18 column and a gradient system of methanol and phosphate solution based on high-performance liquid chromatography. The established multiresidue determination has been applied to several artificially spiked agricultural samples, with the result that the average recoveries were excellent, with the exception of nitenpyram. The limit of detection of the method ranged from 0.01 to 0.03 mg/kg for the insecticides.     

Evaluation of supercritical fluid extraction/aminopropyl solid-phase "in-line" cleanup for analysis of pesticide residues in rice

Supercritical fluid extraction (SFE) and the use of aminopropyl solid-phase material for "in-line" cleanup was evaluated for residue analysis of 22 GC-amenable pesticides in wild- and white-rice samples with a fat content of 1.9 and 0.4%, respectively. After optimizing the extraction conditions on glass beads as inert material and evaluating the fat amount extracted from rice by SFE, the use of Florisil, Celite, Extrelut, Hydromatrix, and an aminopropyl material as fat-retention materials for SFE "in-line" cleanup was assessed, aminopropyl being the most suitable material for this cleanup of fat. Pesticide mean recoveries obtained from rice samples, at fortification levels around 0.5 mg/kg, by means of the SFE/in-line cleanup method finally proposed (15-mL CO2 volume, 50 degrees C temperature, 200 atm pressure, 200 muL of methanol static modifier, and a 1-cm layer of aminopropyl at the bottom of the extraction vessel), ranged between 74 and 98%, except for captafol and dimethoate for which mean recoveries lower than 21% were determined.     

Determination of 49 organophosphorus pesticide residues and their metabolites in fish, egg, and milk by dual gas chromatography-dual pulse flame photometric detection with gel permeation chromatography cleanup

A new method for the quantitative determination of 49 kinds of organophosphorus pesticide residues and their metabolites in fish, egg, and milk by dual gas chromatography-dual pulse flame photometric detection was developed. Homogenized samples were extracted with acetone and methylene chloride (1 + 1, v/v), and then the extracts were cleaned up by gel permeation chromatography (GPC). The response of each organophosphorus pesticide showed a good linearity with its concentration; the linearity correlation was not less than 0.99. The detection limits (S/N = 3) of pesticides were in the range of 0.001-0.025 mg kg?1. The recovery experiments were performed by blank sample spiked at low, medium, and high fortification levels. The recoveries for fish, egg, and milk were 50.9-142.2, 53.3-137.2, and 50.3-139.4% with relative standard deviations (RSD, n = 6) of 2.3-24.9, 4.3-26.7, and 2.8-32.2%, respectively. The method was applied to detect organophosphorus pesticides in samples collected from the market, and satisfactory results were obtained. This quantitative method was highly sensitive and exact and could be applied to the accurate determination of organophosphorus contaminants in fish, egg, and milk.     

Analysis of pesticide residues in fruit and vegetables after cleanup with solid-phase extraction using ENV+ (Polystyrene-divinylbenzene) cartridges.

A rapid and simple cleanup procedure for the existing multimethod using solid-phase extraction columns to measure pesticide concentrations in fruit and vegetables is presented. After extraction with ethyl acetate, the sample is passed through ENV+, polystyrene-divinylbenzene extraction column, and eluted with ethyl acetate and injected on to capillary GC columns connected to various detectors. The extraction column has the capacity to retain a broad range of pesticides and is widely used in environmental water samples. In this paper, the sample is extracted in an organic solvent. In contrast to what could be expected, it has been found that the column has the capacity to retain pesticides when used as the normal phase.     

Levels and incidences of pesticide residues in various foods and animal feeds analyzed by the Luke multiresidue methodology for fiscal years 1982-1986

During a 5 year period from 1982 to 1986, the FDA Los Angeles District Laboratory analyzed 19,851 samples of domestic and imported food and feed commodities for pesticide residues. A single, rapid, multiresidue method was used. The resultant data have been compiled showing the commodities sampled and the identity and range of levels of pesticide residues detected, including an indication of those residue findings that did not comply with U.S. federal tolerance levels. The residue data presented should not be viewed as being representative of the U.S. food supply; rather, the results are indicative of a surveillance- and compliance-oriented sampling of various food shipments collected by the Los Angeles District.     

Determination of Mirex in human blood serum containing polychlorinated biphenyls by using packed column gas chromatography.

An analytical method has been developed that uses electron capture/gas-liquid chromatography to determine Mirex in serum containing polychlorinated biphenyls (PCBs) (Aroclor 1260). With this method, 0.2 ppb Mirex can be determined in 4 mL serum that also contains 10 ppb PCBs. The method provides approximately 70% recovery of Mirex at 1.0 and 3.5 ppb. The coefficients of variation are 4.5 and 4.6% at 1.0 and 3.5 ppb, respectively. In a cooperative study with the Ohio Department of Health, the Centers for Disease Control used this method to determine the extent of exposure of Salem, OH, residents to Mirex. Confirmation of Mirex was obtained by using high resolution gas chromatography and high resolution mass spectrometry.     

Multiresidue method for the analysis of pesticide residues in fruits and vegetables by accelerated solvent extraction and capillary gas chromatography

An analytical procedure using accelerated solvent extraction and capillary gas chromatography with electron capture and flame photometric detections was developed to simultaneously determine residues of different pesticides in fruits and vegetables. Single laboratory validation of the method was carried out for 28 compounds selected from eight pesticide classes, in blank and fortified samples of fresh pear, cantaloupe, white potato, and cabbage. The method had to meet specific established validation criteria for regulatory purposes applicable to our laboratory. At each of the two fortification levels studied, 24 of the 28 pesticides gave recoveries of more than 70% with a coefficient of variation of less than 10%. With respect to existing procedures, the method showed acceptable limits of detection (from 0.0019 to 0.14 microg/g depending on the pesticide and matrix) while minimizing environmental concerns, time, and labor.     

Analysis of pesticide residues by chemical derivatization. II. N-methylcarbamates in natural water and soils.

A method for the quantitative determination of several N-methylcarbamates in natural waters and the applicability of the derivative to soil samples using a previously published extraction procedure are described. After extraction of the carbamates from the substrate, the carbamates are hydrolyzed in a 10% methanol-potassium hydroxide solution to form the phenolic hydrolysis products, which are isolated and derivatized with pentafluorobenzyl (PFB) bromide to produce the PFB ether derivatives. The PFB derivatives are cleaned up and fractionated on a silica gel microcolumn and determined by electron capture gas-liquid chromatography (GLC). Eight organophosphate pesticides and 2 phthalate acid esters that hydrolyze to phenols or phthalic acid were evaluated as potential interferences and were found not to interfere with any of the carbamates tested. Quantitative determinations of 0.1 mug carbofuran and 3-ketocarbofuran and 0.5 mug carbaryl, metmercapturon, and Mobam in a 1 L water sample are possible. Propoxur was not determined at levels less than 1 mug/L due to the short GLC retention time of the derivative and interferences from the reagents at the lower levels.