Gas chromatographic determination of maleic hydrazide residues in potato tubers

A gas chromatographic (GC) method is described for the determination of maleic hydrazide residues in potato tubers by oxidation of maleic hydrazide with aqueous lead dioxide to 3,6-pyridazinedione in the presence of cyclopentadiene. The reaction product, a volatile Diels-Alder adduct, could be detected in potatoes at levels in excess of 0.05 ppm with an electron capture detector. Recoveries of maleic hydrazide (as the Diels-Alder adduct) from potatoes at fortification levels of 0.1 to 10 ppm averaged 91.7%.     

Simplified cleanup and liquid chromatographic ultraviolet determination of linuron and three metabolites in potatoes

A simple and efficient method is presented for the extraction, cleanup, and liquid chromatographic (LC) determination of linuron and 3 of its metabolites, 3-(3,4-dichlorophenyl)-1-methyl urea (DCPMU), 3-(3,4-dichlorophenyl) urea (DCPU), and 3,4-dichloroaniline (DCA), in potatoes. Samples are extracted with acetone, partitioned into dichloromethane-hexane (1 + 1), and cleaned up using disposable silica cartridges. LC determination is performed using a LiChrosorb NH2 5 microns column, with an isopropanol-isooctane gradient mobile phase and UV detection at 248 nm. Recoveries of linuron and 2 of the metabolites from untreated samples fortified at 0.02-2 micrograms/g ranged from 80 to 102%, while recoveries for the metabolite DCA ranged from 60 to 78%. The detection limit was 0.015 micrograms/g for linuron and each metabolite; the minimum quantitation level was 0.5 micrograms/g. The developed method was applied to potato samples from a field experiment.     

Simplified cleanup and gas chromatographic determination of organophosphorus pesticides in crops

A simple and efficient cleanup method for gas chromatographic determination of 23 organophosphorus pesticides in crops including onion is described. The sample was extracted with acetone. The extract was purified with coagulating solution, which contained ammonium chloride and phosphoric acid, and then filtered by suction. The filtrate was diluted with NaCl solution and reextracted with benzene. The organic layer was evaporated and injected into a gas chromatograph equipped with a flame photometric detector (FPD) and fused silica capillary columns (0.53 mm id) coated with silicone equivalent to OV-1701, OV-1, and SE-52. Onion extract, which contained FPD interferences, was cleaned up on a disposable silica cartridge. Recoveries of most organophosphorus pesticides from spiked crops: mandarin orange, tomato, spinach, sweet pepper, broccoli, lettuce, and onion at levels of 0.02-0.28 ppm, exceeded 80%, but the water-soluble pesticides dichlorvos and dimethoate gave poor recoveries in all crops; the nonpolar pesticides disulfoton, chlorpyrifos, fenthion, prothiophos, and leptophos were not recovered quantitatively in spinach, sweet pepper, broccoli, and lettuce. IBP, edifenphos, phosmet, and pyridaphenthion were not recovered from onion because of adsorption to the silica cartridge. The detection limits ranged from 1.25 to 17.5 ppb on a crop basis.     

High pressure liquid chromatographic determination of methomyl and oxamyl on vegetable crops

A reverse phase high pressure liquid chromatographic method is presented for the separation and determination of residues of the carbamates oxamyl and methomyl on vegetables. A liquid-liquid extraction and cleanup procedure is applied to the vegetable extract. Samples are eluted from a muBondapak C18 column and quantitated by ultraviolet absorbance at 240 nm. Recovery data for vegetable samples spiked at 2 ppm are presented.     

Ion-pair extraction cleanup for liquid chromatographic determination of bentazon in crops and soil

Bentazon was selectively extracted as an ion pair with tetrabutylammonium ion into dichloromethane. This technique was used to clean up crop and soil samples before determination of bentazon by reverse phase liquid chromatography and UV detection. Recoveries from potatoes, cucumbers, wheat grain, and clay soil were 77-103%, with a detection limit of 0.02 mg/kg.     

High-speed liquid chromatographic determination of o-phenylphenol residues in citrus products.

A method is presented for the quantitative analysis of o-phenylphenol residues in citrus oils, encapsulated flavors, and dried meal. The method utilizes high-speed liquid chromatography for the determination after specific sample preparations for each material. These preparations include hexane extraction of acidified basic extracts or steam distillation and extraction. The limit of the analysis is less than 1 ppm with an analysis time of less than 45 min.     

High-speed liquid chromatographic determination of biphenyl residues in citrus products.

A simple, direct, and rapid method is given for the analysis of citrus oils for the fungistat biphenyl by high-speed liquid chromatography. The method is extended to orange juice and various "dry flavors" by an extraction procedure. Analytical limits are less than 1 ppm without need for any cleanup or concentration steps.     

High pressure liquid chromatographic determination of naphthaleneacetic acid residues in apples.

An ion-suppression reverse phase high pressure liquid chromatographic method is described for determining naphthaleneacetic acid (NAA) residues in apples. Samples are extracted with acidic chloroform, filtered through pre-acidified Hy-Flo Supercel, and cleaned up by acid-base partitioning. The extract can be successfully chromatographed on either a muLiChrosorb NH2 or muBondapak C18 column and quantitated by using a variable wavelength ultraviolet detector set at 220 nm. The mobile phase is acetonitrile-water (20 + 80) buffered to pH 3.5 (MULiChrosorb column) or pH 5.2 (MUBondapak column) and flowing at 1.0--2.0 ml/min. Recoveries ranged from 86 to 98%. The minimum detectable amount was 0.5 ng, which easily permitted the quantitation of 0.01 ppm NAA in 50 g sample. A fluorometric detector was 4 times as sensitive, using an excitation wavelength of 220 mm and monitoring the emission at 340 nm. For this detector, the minimum detectable amount was 0.12 ng NAA.     

Simplified extraction and cleanup for multiresidue determination of pesticides in lanolin

In the proposed method, a light petroleum solution of lanolin (wool fat) is adsorbed on diatomaceous earth in an Extrelut column, and the pesticides are eluted with acetonitrile saturated with light petroleum. After evaporation to a small volume, the extract is subjected to solid-phase extraction (SPE) on a C-18 column. The acetonitrile eluate is evaporated to dryness and the residue is taken up in light petroleum. Organophosphorus pesticides are determined by temperature-programmed gas chromatography (GC) on a wide-bore column using a flame photometric detector in the phosphorus mode. Organochlorine pesticides are determined after miniaturized Florisil cleanup by classic GC on an OV-17/QF-1 packed column, using an electron capture detector. This procedure is more rapid and straightforward than the time-consuming AOAC extraction method, 29.014. Cleanup was better and the results obtained were comparable. Recoveries for 13 organochlorine and organophosphorus pesticides, frequently found in lanolin, ranged from 80 to 90%.     

Improved cleanup for gas chromatographic determination of propiconazole residues in soil, wheat grain, straw, and leaves

A simple and sensitive method is described for determination of propiconazole, a new type of broad-spectrum systemic fungicide, in soil, wheat grain, straw, and leaves. Pesticide residues in or on grain and green plant materials are extracted with methanol (or a mixture of methanol and water (4 + 1), for soil), partitioned into methylene chloride, and cleaned up on an alumina column for grain and soil or an activated charcoal column for green plant materials. The amount of residue is quantitatively measured by gas chromatography using an alkali flame ionization detector in the nitrogen-sensitive mode. Recoveries from soil, grain, and green plant materials fortified at 0.1-5 mg/kg are better than 80%. The practical detection limits of this method are 0.01 mg/kg in grain and soil and 0.02 mg/kg in green plant materials.     

Simplified multiresidue method for liquid chromatographic determination of N-methyl carbamate insecticides in fruits and vegetables

A simplified method is described for determining 7 N-methyl carbamates (aldicarb, carbaryl, carbofuran, methiocarb, methomyl, oxamyl, and propoxur) and 3 related metabolites (aldicarb sulfoxide, aldicarb sulfone, and 3-hydroxy carbofuran) in fruits and vegetables. Residues are extracted from crops with methanol; coextractives are then separated by gel permeation chromatography (GPC) or GPC with on-line Nuchar-Celite cleanup for crops with high chlorophyll and/or carotene content (e.g., cabbage and broccoli). Carbamates are separated on a reverse-phase liquid chromatography column, using a methanol-water gradient mobile phase. Separation is followed by postcolumn hydrolysis to yield methylamine, and the formation of a fluorophore with o-phthalaldehyde and 2-mercaptoethanol prior to fluorescence detection. Recovery data were obtained by fortifying 5 different crops (apples, broccoli, cabbages, cauliflower, and potatoes) at 0.05 and 0.5 ppm. Recoveries averaged 93% at both fortification levels except for the very polar aldicarb sulfoxide for which recoveries averaged around 52% at both levels. The coefficient of variation of the method at both levels is less than 5% and the limit of detection, defined at 5 times baseline noise, varies between 5 and 10 ppb, depending on the compound.     

Use of the Mycosep multifunctional cleanup column for liquid chromatographic determination of aflatoxins in agricultural products.

A liquid chromatographic (LC) technique has been developed that uses the Mycosep multifunctional cleanup (MFC) column. MFC columns provide a rapid 1-step extract purification. They are designed to retain particular groups of compounds that may create interferences in analytical methods. At the same time, MFC columns allow compounds of interest to pass through. In the method presented, test samples are extracted in a blender with acetonitrile-water (9 + 1). A portion of the extract is forced through an MFC column designed especially for analysis of numerous mycotoxins. Analytical interferences are retained, while aflatoxins pass through the column. Aflatoxins B1 and G1 are converted to their hemiacetals by heating a mixture of purified extract and water-trifluoroacetic acid-acetic acid (7 + 2 + 1) at 65 degrees C for 8.5 min. An aliquot of this mixture is analyzed by isocratic LC with acetonitrile-water mobile phase and fluorescence detection. A detection limit of less than 0.5 ng/g for aflatoxin B1 was obtained. Average recoveries greater than 95% total aflatoxins (B1, B2, G1, and G2) and coefficients of variation of less than 3% were obtained. The method was successfully applied to the following commodities: corn, almonds, pista-chios, walnuts, peanuts, Brazil nuts, milo, rice, cottonseed, corn meal, corn gluten meal, fig paste, and mixed feeds.     

Improved cleanup and derivatization for gas chromatographic determination of monosodium glutamate in foods

A gas chromatographic procedure is described for determining monosodium glutamate (MSG) in several types of food. A sample is extracted with acetone-water (1 + 1). Acetone is evaporated and an aliquot of the extract is buffered with 1M NH4OH-1M NH4Cl pH 9 solution, and chromatographed directly on a column of QAE Sephadex A-25 that has been pretreated with the same buffer. MSG is eluted with 0.1N HCl, and a portion of the eluate is evaporated to dryness and reacted with dimethylformamide(DMF)-dimethylacetal to form the glutamic acid derivative, which is injected into a gas chromatograph and measured by flame ionization detection. Recoveries of MSG from sample fortified at 5-500 mg ranged from 92.8 to 100%.     

Liquid chromatographic determination of cephapirin residues in milk

A liquid chromatographic (LC) method was developed for quantitative determination of cephapirin residues in milk that also resolved cephapirin from ampicillin, cloxacillin, and penicillin G. Diluted milk was passed through a C18 cartridge on which the cephapirin was adsorbed; then, interfering material was removed by washing with water and methylene chloride and cephapirin residues were eluted with methanol-acetonitrile (25 + 75). After drying, residues were dissolved in the mobile phase for injection. The LC system had an ultrasphere-ODS column with RP-18 Spheri-10 guard column and a UV detector with a 254 nm filter. The mobile phase was 85% sodium acetate (0.01M) and 15% methanol-acetonitrile (25 + 75) with a flow rate of 1 mL/min. Sensitivity was 20 ppb or less with a recovery of 61-80% in the range studied. Other beta-lactam antibiotics tested did not interfere with detection of cephapirin. Analysis of 30 samples of commercial homogenized milk obtained for a survey of antibiotics in consumer milk in Canada revealed no detectable cephapirin residues.     

High-performance liquid chromatographic determination of the glycoalkaloids alpha-solanine and alpha-chaconine in 12 commercial varieties of Mexican potato

The glycoalkaloid content in 12 commercial varieties of Mexican potatoes was measured by HPLC in both the peel and the flesh of the potato. The principal glycoalkaloids alpha-solanine and alpha-chaconine were present in higher concentration in the peel than in the flesh of all varieties. The main alkaloid in the peel of the potatoes was alpha-chaconine and comprised about 65-71% of the total glycoalkaloids. The high concentration of alpha-chaconine in peel, which is more toxic than alpha-solanine, gives more protection to the tuber against predators. The total alkaloids in the peel of Alpha, Juanita, Michoacan, Norte?a, Rosita, and Tollocan varieties were higher than the limit recommended for food safety. However, the peel represents less than 10% of the total tuber in most of the varieties. The total alkaloids contained in the peel of Atzimba, Lopez, Marciana, Montsama, Murca, and Puebla was lower than the limits recommended for food safety. The glycoalkaloid content in the boiled peeled potatoes was less than 9 mg/100 g but in Alpha, Montsama, and Puebla varieties, both glycoalkaloids were absent. According to the results, the consumption of the 12 commercial varieties of Mexican potatoes does not represent any danger to human health.     

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.