GC/MIP/AED Method for Pesticide Residue Determination in Fruits and Vegetables

This research describes the results of a gas chromatography/microwave induced plasma/atomic emission detection (GC/MIP/AED) method performed on a Hewlett-Packard 5921A system for pesticide residue analysis in fruits and vegetables. Atotal of 6 experiments were conducted: (1) sensitivity and linearity studies for elements S, P, CI, and N by analyzing dursban; (2) a study of instrument response to CI concentration in pesticide molecules; (3) organochlorinated pesticide recoveries; (4) organophosphate pesticide recoveries; (5) carbamate pesticide recoveries; and (6) investigation of metallic pesticides with pllctran and vendex as standards. The rank according to sensitivity and linearity was found to be as follows: S-181>P-178>CI-479>N-174. Instrument response to the concentration of chlorine atoms in the pesticide molecule was linear, with a correlation coefficient of 0.89. Recoveries of organochlorinated pesticides were 91.7-109.3%, with the exception of citrus, whose recovery was affected by coeluting Interferences. Organophosphate recoveries were 73.2% or higher, except for the cygon oxygen analog, which degraded in the GC system under all circumstances. Carbamate recoveries were inconsistent quantitatively; however, the information generated from elements N and S were useful for qualitative confirmation of other methods, such as LC postcolumn derivatization analysis. Overall, the GC/MIP/AED method is powerful for qualitative confirmation in pesticide residue analysis. The instrument’s capability of acquiring multi-elements (CI and P) selectively and accurately is an alternative method for organochlorinated and organophosphate pesticide residue analyses. In addition, the GC/MIP/AED system is easy to use, simple to maintain, and its chromatograms can be interpreted by any chromatography analyst without much prior training.

Improved Method for Determination of Polynuclear Aromatic Hydrocarbons in Pharmacopoeial Paraffin and Mineral Oils

An improved method has been developed for quantitative determination of poiynuciear aromatic hydrocarbons (PAHs) in pharmacopoeial paraffin and medicinal white oil samples. This new method combines 2 liquid-liquid partition and adsorption chromatography procedures with a 2-step purification on Sephadex LH 20 and liquid chromatography with fluorometric determination. Selective elution of PAHs results in absence of background fluorescence. The minimum detectable level ranges from 0.2 ppt for benzofluoranthene isomers to 200 ppt for acenaphthene. Recoveries of PAHs added at 7 ppm varied from 92.1 to 111.4%. When a variety of medicinal white oil samples were analyzed by this improved method, 27 PAHs were identified, including 11 suspected carcinogens. Their identities were confirmed by capillary gas chromatography.

Separation of Clethodim Herbicide from Acid and Photodegradation Products by Liquid Chromatography

Clethodim, (E,E)-(±)-2-[1-[[(3-chloro-2-propenyl)oxy]lmino] propyl]-5[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one, is stable in acetonitrlie, but the Inclusion of water induced degradation in the dark. Addition of acetic acid to the mobile phase did not increase degradation; however, it did improve peak symmetry and liquid chromatographic (LC) separation, with the optimum resolution at 0.75% acetic acid. The extinction coefficient for clethodim at 254 nm did not change in acetonitrlie with addition of water or acetic acid. The LC detector responded linearly to clethodim in the 0.7-400 ppm range. Separate solvent gradient programs (40 min each) were developed for separation of acid degradation products (ADPs) and the photodegradation products (PDPs). The inclusion of cobalt or silver nitrate to the mobile phase did not improve separations. A minimum of 31 and 19 products formed during photolytic and hydrolytic degradation of clethodim, respectively. PDPs were more polar than ADPs. Reproducibility of this method was considered to be acceptable for separation of ADPs and PDPs of clethodim.

An Analytical Survey of Aflatoxins in Tissues from Swine Grown in Regions Reporting 1988 Aflatoxin-Contaminated Corn

A joint project was undertaken by the Food Safety and Inspection Service (FSIS) and the Agriculture Research Service branches of the U.S. Department of Agriculture to determine the presence of aflatoxins in the U.S. meat supply during a drought year. In 1988, high incidences of aflatoxins occurred in corn grown in regions of the Midwest, Southeast, and South. Six states were identified as having serious aflatoxin contamination in their corn crop: Virginia, North and South Carolina, Texas, Iowa, and Illinois. Swine liver and pillars of diaphragm (muscle) tissues were sampled by federal FSIS inspectors in plants located in these states. A worstcase sampling plan was conducted. Samples were taken in January 1989 from hogs fed corn soon after harvest and in April 1989 from hogs fed corn originally stored and then fed in the spring. A modification of the official AOAC method for the thin-layer chromatography (TLC) determination of aflatoxins in animal tissue was used to permit quantitation by LC with fluorescence detection. The official AOAC TLC confirmation of identity method was used to confirm all positive samples with B1 concentrations >0.04 ppb and M1 concentrations >0.1 ppb. Sixty samples in the January group and 100 samples in the April group were assayed. Concentrations of aflatoxins B1 and M1 in the first group of pig livers ranged from 0.04 to 0.06 ppb. The identity of aflatoxin Bi was confirmed in all positive samples. Aflatoxin M1 could not be confirmed in any of the positive liver samples because the method was insufficiently sensitive for this aflatoxin. No positive muscle samples were found. In the second set, 9 positive livers were determined with B1 concentrations from 0.01 to 0.24 ppb and M1 concentrations from 0.03 to 0.44 ppb. Two samples contained M1 only. None of the corresponding muscle samples contained aflatoxins. Of the 12 positive samples, 5 were from Iowa, 4 from South Carolina, 2 from North Carolina, and 1 from Illinois. Aflatoxins were not detected in any of the samples from Texas or Virginia. One sample from North Carolina contained more than 0.5 ppb total aflatoxins. Blind recovery studies were conducted by including an artificially contaminated liver sample for every 6 samples assayed, and 1 uncontaminated liver sample for every 18 samples. Recoveries of aflatoxins B1, d , and M1 were 71.8%, 73.2%, and 69.8% respectively.

Limited Survey of Residual Tetracyclines in Tissues Collected from Diseased Animals in Aichi Prefecture, Japan

Tissues were collected to survey the actual conditions of tetracycline antibiotics (TCs) residues in slaughtered animals that did not pass inspection at slaughterhouses in Aichi Prefecture, Japan, because of the presence of disease symptoms. Tissues were analyzed by liquid chromatography. Among 271 samples, 49 (18.1%) were positive for oxytetracycline (OTC), 5 (1.8%) for chlortetracycline (CTC), and 5 (1.8%) for doxycyclfne (DC), respectively. One sample (cattle kidney) was positive for both OTC and DC. However, tetracycline was not detected in any samples. Percentage frequencies of TCs residues were 29.1% (37/127) and 15.2% (22/144) for cattle and hogs, respectively. Kidney samples showed higher incidence of TCs residues and 1.5-7 times higher residual concentrations than liver and miscellaneous samples.

Separation and Determination of Diesel Contaminants in Various Fish Products by Capillary Gas Chromatography

A semiquantitative capillary column gas chromatographic method Is described for the determination of diesel fuel contamination in various canned seafood products. The diesel contaminants are separated from the fish sample by steam distillation, with little carry-over of interfering intrinsic materials such as fish oils. The diesel fuel is extracted from the condensate with n-hexane, and the extract is analyzed on an SPB-1 fused silica capillary column. The efficiency of recovery of diesel fuel added to canned seafood at levels of 40-400 ppt ranged from 72 to 102%. With the additional step of concentrating the hexane extract, the sensitivity of this procedure may be increased at least 10-fold. This procedure can detect the differences among diesel fuel grades No. 1,2, and 5, and variations within diesel grade No. 2, and thus may be useful in determining the type of petroleum contaminants present in various canned fish products.

Bacillus stearothermophilus Disk Assay for Determining Ampicillin Residues in Fish Muscle

The Bacillus stearothermophilus disk assay for penicillin in milk (AOAC official method) was adapted for the determination of ampicillin in fish muscle. The method was evaluated in 2 species of cultured fish: channel catfish and striped bass. Recoveries of ampicillin ranged from 99 to 104% when muscle specimens from both species were spiked at concentrations of 0.025-1.00 μg/g. The lower limit of determination (LOD) was 0.025 μg/g. The assay was applied to monitor the elimination of ampicillin from the muscle of striped bass after intravascular administration (dosage of 10 mg/kg body weight). The mean concentrations in the muscle declined from 1.160 μg/g at 2 h to 0.063 μg/g at 18 h. The half-life of ampicillin in the muscle was 3.6 h. Ampicillin concentrations were below LOD at 24 h. No inhibitory activity was observed in the muscle of control fish.

Supercritical Fluid Extraction/Enzyme Assay: A Novel Technique to Screen for Pesticide Residues in Meat Products

The novel combination of supercritical fluid extraction (SFE) with an enzyme assay system has been used to screen meat products to detect the presence of pesticides. Analytes are collected in water by expanding supercritical carbon dioxide to atmospheric pressure through a restrictor and into an aqueous phase. The solution is then tested for the presence of pesticide residues by enzyme assay. Two experimental approaches have been used. Alachlor-fortified lard and bovine liver were monitored by static SFE coupled with an enzyme immunoassay. SFE of carbofuran-fortified frankfurters was coupled with an enzyme assay based on cholinesterase inhibition. A major benefit of the SFE/enzyme assay technique over conventional screening techniques is that the analyst is not exposed to organic solvents.

Multipesticide Determination in Surface Water by Gas Chromatography/Chemical Ionization/Mass Spectrometry/Ion Trap Detection

An improved method for the determination of trace levels of pesticides in surface water has been developed and was used to analyze 20 target pesticides in New Jersey. Pesticides were extracted from 2 L water samples, using a mixture of XAD-2 and XAD-7 resins, and were determined by gas chromatography/chemical ionization mass spectrometry with ion trap detection. Average recoveries (performed in triplicate at the 1 ppb level, except for captan and chlorothalonil at 5 ppb) were between 75 and 113%, with an average coefficient of variation of 9%. Most of the pesticides (alachlor, atrazine, butylate, carbofuran, chlorpyrifos, diazinon, fonofos, isofenphos, metolachlor, metribuzin, parathion, and simazine) had limits of detection (LODs) of 0.005 ppb or lower, while some (carbaryl, cyanazine, fenamiphos, linuron, pendlmethalin, and terbufos) had LODs between 0.005 and 0.05 ppb. Captan and chlorothalonil had LODs of 1 ppb. Of 31 samples analyzed, 29 contained one or more of the following pesticides: alachlor, atrazine, carbaryl, chlorpyrifos, cyanazine, diazinon, isofenphos, linuron, metolachlor, and simazine in concentrations between trace (<0.025 ppb) and 5.48 ppb.