Analysis of permethrin isomers in composite diet samples by molecularly imprinted solid-phase extraction and isotope dilution gas chromatography-ion trap mass spectrometry.

Determination of an individual's aggregate dietary ingestion of pesticides entails analysis of a difficult sample matrix. Permethrin-specific molecularly imprinted polymer (MIP) solid-phase extraction cartridges were developed for use as a sample preparation technique for a composite food matrix. Vortexing with acetonitrile and centrifugation were found to provide optimal extraction of the permethrin isomers from the composite foods. The acetonitrile (with 1% acetic acid) was mostly evaporated and the analytes reconstituted in 90:10 water/acetonitrile in preparation for molecularly imprinted solid-phase extraction. Permethrin elution was accomplished with acetonitrile and sample extracts were analyzed by isotope dilution gas chromatography-ion trap mass spectrometry. Quantitation of product ions provided definitive identification of the pesticide isomers. The final method parameters were tested with fortified composite food samples of varying fat content (1%, 5%, and 10%) and recoveries ranged from 99.3% to 126%. Vegetable samples with incurred pesticide levels were also analyzed with the given method and recoveries were acceptable (81.0-95.7%). Method detection limits were demonstrated in the low ppb range. Finally, the applicability of the MIP stationary phase to extract other pyrethroids, specifically cyfluthrin and cypermethrin, was also investigated.

Development of an analytical scheme for the determination of pyrethroid pesticides in composite diet samples.

Analysis of an individual's total daily food intake may be used to determine aggregate dietary ingestion of given compounds. However, the resulting composite sample represents a complex mixture, and measurement of such can often prove to be difficult. In this work, an analytical scheme was developed for the determination of 12 select pyrethroid pesticides in dietary samples. In the first phase of the study, several cleanup steps were investigated for their effectiveness in removing interferences in samples with a range of fat content (1-10%). Food samples were homogenized in the laboratory, and preparatory techniques were evaluated through recoveries from fortified samples. The selected final procedure consisted of a lyophilization step prior to sample extraction. A sequential 2-fold cleanup procedure of the extract included diatomaceous earth for removal of lipid components followed with a combination of deactivated alumina and C(18) for the simultaneous removal of polar and nonpolar interferences. Recoveries from fortified composite diet samples (10 microg kg(-1)) ranged from 50.2 to 147%. In the second phase of this work, three instrumental techniques [gas chromatography-microelectron capture detection (GC-microECD), GC-quadrupole mass spectrometry (GC-quadrupole-MS), and GC-ion trap-MS/MS] were compared for greatest sensitivity. GC-quadrupole-MS operated in selective ion monitoring (SIM) mode proved to be most sensitive, yielding method detection limits of approximately 1 microg kg(-1). The developed extraction/instrumental scheme was applied to samples collected in an exposure measurement field study. The samples were fortified and analyte recoveries were acceptable (75.9-125%); however, compounds coextracted from the food matrix prevented quantitation of four of the pyrethroid analytes in two of the samples considered.

Surface-to-food pesticide transfer as a function of moisture and fat content.

Transfer of pesticides from household surfaces to foods may result in excess dietary exposure in children (i.e., beyond that inherent in foods due to agricultural application). In this study, transfer was evaluated as a function of the moisture and fat content of various foods. Surfaces chosen for investigation were those commonly found in homes and included Formica, ceramic tile, plastic, carpet, and upholstery fabric. Each surface type was sprayed with an aqueous emulsion of organophosphates, fipronil, and synthetic pyrethroids. In the first phase of the study, multiple foods (apples, watermelon, wheat crackers, graham crackers, white bread, flour tortillas, bologna, fat-free bologna, sugar cookies, ham, Fruit Roll-ups, pancakes, and processed American cheese) were categorized with respect to moisture and fat content. All were evaluated for potential removal of applied pesticides from a Formica surface. In the second phase of the study, representative foods from each classification were investigated for their potential for pesticide transfer with an additional four surfaces: ceramic tile, plastic, upholstery, and carpet. Moisture content, not fat, was found to be a determining factor in most transfers. For nearly all surfaces, more efficient transfer occurred with increased hardness (Formica and ceramic tile). Comparatively, the polymer composition of the plastic delivered overall lower transfer efficiencies, presumably due to an attraction between it and the organic pesticides of interest.

Radioimmunoassay for Clostridium perfringens Enterotoxin and Its Use in Screening Isolates Implicated in Food-Poisoning Outbreaks.

Fourteen isolates of Clostridium perfringens obtained from food-poisoning outbreaks were screened for enterotoxigenicity using a radioimmunoassay (RIA) that detects 1.0 ng of enterotoxin/ml. Only four of the isolates produced enterotoxin in concentrations too low to be detected by counterimmunoelectrophoresis when grown in Duncan-Strong sporulation (D-S) medium. Substitution of raffinose for soluble starch or addition of theobromine to the medium stimulated enterotoxin production by three of the four enterotoxin-positive isolates. Raffinose and theobromine did not stimulate enterotoxin production by isolates that were enterotoxin-negative in D-S medium. Enterotoxin production by the RIA-positive strains correlated with the numbers of heat-resistant spores they produced. The RIA-negative isolates produced approximately the same numbers of spores/ml as the high enterotoxin producers, and more spores/ml than strain H8 produced under optimum conditions. Therefore, inability to sporulate is not the cause for failure of these isolates to produce enterotoxin. Rabbit ileal loop assays showed that the two isolates that were lowest enterotoxin producers in vitro were highly active in vivo.