Gas chromatographic determination of incurred dimetridazole residues in swine tissues

A gas chromatographic method for determination of 2-hydroxymethyl-1-methyl-5-nitroimidazole (DMZOH), the hydroxy metabolite of dimetridazole, in swime muscle has been developed. The method uses cleanup steps similar to those of an earlier polarographic method. The present method is capable of quantitating levels as low as 2 ppb and detecting less than 1 ppb. Recoveries from 30 control tissues spiked at 1, 2, or 4 ppb averaged 80.4%. Performance of the method in incurred tissue was documented and limited data on the depletion of the metabolite in muscle were generated. The muscle of swine given 150 ppm dimetridazole in feed for 14 days contained less than 1 ppb DMZOH at 12 h withdrawal time.     

Liquid chromatographic determination of chlortetracycline hydrochloride in ruminant and poultry/swine feeds.

A liquid chromatographic (LC) method is described for the determination of chlortetracycline hydrochloride (CTC) in poultry/swine and ruminant feeds in the 10-100 ppm range and in premix. CTC is extracted from ground feed/premix with acidified acetone, and the extract is filtered through a Millex-HV filter or disposable C18 column. The filtrate is partitioned with methylene chloride when additional cleanup is necessary. A Nova-Pak C18 column is used for LC separation with determination at 370 nm. The average recovery of CTC from premix was 95% with a standard deviation (SD) of 1.70 and a coefficient of variation (CV) of 1.79%. The overall average recovery from feeds was 77% with an SD of 3.18 and a CV of 4.10%.     

Rapid liquid chromatographic determination of dimetridazole and ipronidazole in swine feed

A simple and rapid method is described for the determination of dimetridazole (DMZ) and ipronidazole (IPR) in swine feeds at various levels (0.11-110 ppm). The drugs are released from feed by prewetting with a buffer, followed by extraction with either methanol or methylene chloride, depending on the drug level; if necessary, an acid-base cleanup is used before the liquid chromatographic analysis. The analytes are separated on a C18 column and monitored at 320 nm for detection and quantitation. Recoveries of DMZ from several feed formulations averaged 108% at the 92.8 ppm level with a standard deviation (SD) of 4.00% and a coefficient of variation (CV) of 3.70%, 101% at the 11.2 ppm level with an SD of 11.9% and a CV of 11.8%, and 100% at the 0.112 ppm level with an SD of 9.27% and a CV of 9.25%. Recoveries of IPR averaged 77.1% at the 12.9 ppm level with an SD of 1.75% and a CV of 2.27%; IPR recoveries averaged 35.2% at the 0.129 ppm level with an SD of 3.39% and a CV of 9.63%.     

Simplified cleanup and liquid chromatographic determination of oxamyl residues in potato tubers

A simple and efficient method is presented for the extraction, cleanup, and liquid chromatographic (LC) determination of oxamyl residues in potato tubers. Samples are extracted with methanol, partitioned into dichloromethane, and cleaned up using Sep-Pak Florisil cartridges. LC determination is performed using a Zorbax PSM 60 size exclusion column with an acetonitrile-water (1 + 9) mobile phase and UV detection at 254 nm. Recovery of oxamyl from spiked control tubers averaged 94.1 and 85.9% at fortification levels of 0.4 and 0.08 micrograms oxamyl/g tuber, respectively. The minimum detectable concentration of oxamyl by this method is 0.01 micrograms/g.     

Gas chromatographic determination of pentachlorophenol in gelatin: collaborative study

Eleven collaborators participated in this study of a gas chromatographic method for the determination of pentachlorophenol (PCP) in gelatin. Following acid hydrolysis of a 2 g sample, PCP is extracted with hexane and partitioned into KOH solution. After reacidification, PCP is again extracted with hexane for determination by electron capture gas chromatography on a 1% SP-1240DA column. Three duplicate practice samples (0.0, 0.5, and 1.5 ppm) and 5 blind duplicate collaborative samples (0.0, 0.02, 0.1, 0.5, and 2.0 ppm) were analyzed by each collaborator. Mean recoveries of PCP in the collaborative samples ranged from 88% at the 0.02 ppm fortification level to 102% at the 0.1 ppm level; the overall mean recovery was 96%. Interlaboratory coefficients of variation ranged from 16.4% for the 0.1 ppm fortification level to 22.9% for the 0.5 ppm level; the overall interlaboratory coefficient of variation was 19.5%. The method has been adopted official first action.     

Thin layer chromatographic determination of citrinin.

A thin layer chromatographic (TLC) method is described for the determination of citrinin in feeds. Citrinin is extracted from feed with methanol and water, the mixture is made alkaline with 10% sodium carbonate, and the aqueous solution is filtered and extracted with chloroform to remove most of the interfering materials. The aqueous layer is acidified with 2N HCl and extracted with chloroform. The chloroform extract is concentrated and spotted on a thin layer chromatographic (TLC) plate which is developed in chloroform-acetone-ethanol-water (60 + 40 + 10 + 1). The citrinin is viewed under ultraviolet light after TLC. Either visual or fluorodensitometric quantitation is used. Recoveries of citrinin from various feed samples spiked at levels of 2.0--5 micrograms/g were 75--92%. The proposed method can detect 0.5 micrograms/g feed, including corn, silage, ready mixed feeds, and feed pellets.     

Determination of ochratoxin A in animal feed and cereal grains by liquid chromatography with fluorescence detection

A liquid chromatographic (LC) method is described for determination of ochratoxin A in animal feeds and cereal grains. Samples are initially extracted with chloroform-ethanol (8 + 2) and 5% acetic acid in water. Extracts are purified using a silica gel cartridge followed by a cyano cartridge. The samples are evaporated, diluted to a known volume, and analyzed using a 10 cm column of 3 micron C18 and a fluorescence detector. The method was applied to a variety of animal feeds and cereal grains at levels of 1.0-0.005 ppm added ochratoxin A. The overall recovery was 90.6% +/- 3.6.     

Determination of polybrominated biphenyl residues in dry animal feeds.

A new procedure is described for the determination of polybrominated biphenyls (PBBs) in dry animal feeds and developmental results are discussed. Finely ground feed is packed into a chromatographic column containing Celite and then eluted with methylene chloride. The concentrated extract is cleaned up by elution with petroleum ether through Florisil before gas-liquid chromatographic quantitation. Chromatograms thus obtained were essentially free of the interfering peaks encountered when using AOAC methods for pesticide residues in dry products. Results of feed analyses by the proposed procedure averaged 30% higher than those obtained by AOAC procedures. Recoveries of PBBs from samples fortified at levels of 0.04 to 0.4 ppm ranged from 90 to 104%, with an average of 98%.     

Determination of N-nitrosodimethylamine levels in some Canadian 2,4-D amine formulations

Levels of N-nitrosodimethylamine (NDMA) were determined in 112 samples of 2,4-dichlorophenoxyacetic acid, (2,4-D), formulated as the dimethylamine salt, collected over a 2 year period from products on the Canadian market. A sample aliquot is partitioned with dichloromethane, and the co-extracted dimethylamine is removed by cleanup on a silica gel column. The eluates containing NDMA are concentrated, an internal standard of N-nitrosodipropylamine is added, and nitrosamine levels are determined using a gas chromatograph interfaced with a thermal energy analyzer. Recoveries of NDMA and N-nitrosodiethylamine spiked into samples were 103 +/- 16 and 96.3 +/- 9.8%, respectively. Of the 112 samples analyzed, 92 were below 1 part per million (ppm) relative to the amount of 2,4-D in the samples, 16 were between 1 and 5 ppm, and 4 were greater than 5 ppm. The gas chromatographic column used is compared to a conventional packing material for volatile nitrosamine analysis. Formation of NDMA during cleanup and analysis was shown not to occur.     

Spectrofluorometric determination of BAY Vp 2674 residues in poultry tissues

A spectrofluorometric (SPF) method is described for determination of residues of BAY Vp 2674 in chicken and turkey tissues. The drug is extracted from tissues with dichloromethane-methanol. The organic extract is concentrated to near dryness and cleaned up by a series of partitionings with n-hexane, then dichloromethane against pH 2 buffer and dichloromethane against pH 12 buffer. The drug is partitioned into dichloromethane from pH 7 buffer and concentrated to dryness. The residue is dissolved in pH 3.5 buffer for SPF analysis at 282 nm (excitation) and 445 nm (emission). Recoveries of BAY Vp 2674 added to chicken and turkey tissues at levels of 0.05, 0.1, and 0.2 ppm range from 86 to 92% with a coefficient of variation of 3.4-10.1%. Detection limit is 0.02 ppm. A liquid chromatographic confirmatory procedure is also described, with ultraviolet and fluorescence detection.     

High performance liquid chromatographic determination of nine phenolic antioxidants in oils, lards, and shortenings

A simple, rapid technique is described for the determination of 2- and 3-tert-butyl-4-hydroxyanisole (BHA), tert-butylhydroquinone (TBHQ), 3,5-di-tert-butyl-4-hydroxytoluene (BHT), 2,6-di-tert-butyl-4-hydroxymethylphenol (Ionox-100), 2,4,5-trihydroxybutyrophenone (THBP), propyl gallate (PG), octyl gallate (OG), dodecyl gallate (DG), and nordihydroguaiaretic acid (NDGA) in vegetable oils, lards, and shortenings. The antioxidants are partitioned from hexane-oil into acetonitrile, concentrated under vacuum, and determined by reverse phase, gradient elution, high performance liquid chromatography with detection at 280 nm. The mobile phase is water-acetonitrile with 5% acetic acid. With this system, only Ionox-100 and OG are not resolved. Recoveries from soya-sunflower seed oil spiked at 16 and 100 ppm and from lard at 32 ppm for 8 of the 9 antioxidants ranged from 96 to 103%, 100 to 102%, and 98 to 102%, respectively. The recoveries of BHT, due to incomplete extraction, were 84, 85, and 87%, respectively.     

Determination of ivermectin in medicated swine feeds at the 2 ppm concentration level

An analytical method has been developed that is applicable to the determination of Ivermectin in medicated feeds at the 2 ppm concentration level. It is based upon liquid chromatographic analysis with a reverse-phase column and ultraviolet detection. After the drug is extracted from the feed into methanol, an analytical sample is prepared by the consecutive use of column chromatography on alumina and solid-phase extraction on Sep-Pak C18 and silica cartridges. This procedure has been applied to the concentration range 0.50-3.0 ppm of Ivermectin in feed with an accuracy of +/- 2% mean relative error and a precision of +/- 2% relative standard deviation at the 2 ppm concentration level.     

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.     

Liquid chromatographic determination of tetracycline residues in animal feeds

A liquid chromatographic method for the multiresidue determination of tetracyclines (TCs) in feeds is described. The levels of quantitation were 10 ppm each for tetracycline-HCl (TC), oxytetracycline (OTC), and chlortetracycline-HCl (CTC); the detection limit was 40 ppb for each. The calibration curves were linear between 2.5 and 100 ppm. The procedure involved double extraction with pH 2.0 and pH 4.5 McIlvain buffers, cleanup on a Sephadex LH-20 column, separation on a Nova-Pak C18 column, and detection at 370 nm. Recoveries of 10 micrograms/g of each TC in multiresidue feed samples ranged from 55.8 to 75.5% for OTC, 71.6 to 100% for TC, and 22.4 to 60.6% for CTC. The identities of the TCs were confirmed by thin layer chromatography.     

High-performance liquid chromatographic determination of strychnine in grain baits.l.

A simple and rapid high-performance liquid chromatographic procedure is described for the determination of strychnine. Grain baits containing strychnine alkaloid are ground, mixed, and extracted by shaking with chloroform. Without further cleanup, extract filtrates are injected directly into a liquid chromatograph. Chromatography is complete within 7 min and peak heights are used for quantitation. Separations were made on a 30 cm times 4 mm id stainless steel column packed with mu Porasil (8-12 mum silica). The eluting solvent was methanol-chloroform (10+90) at a flow rate of 2.0 ml/min. Recovery of spiked samples ranged from 91.5 to 95.2%. Confirmation of strychnine from a commercial sample was made by high resolution mass spectrometry with mass agreement to 1.2 ppm.     

Determination of methylene chloride, ethylene dichloride, and trichloroethylene as solvent residues in spice oleoresins, using vacuum distillation and electron capture gas chromatography.

A quantitative gas chromatographic (GC) method is described for the determination of residual methylene chloride, ethylene dichloride, and trichloroethylene in spice oleoresins. The proposed method involves vacuum distillation in a closed system with toluene as a carrier solvent. Quantitation by electron capture GC on Porapak Q is facilitated by water extraction and by the addition of trans-1,2-dichloroethylene as an internal standard. Recoveries from oleoresins spiked at 30, 15, and 6 ppm ranged from 93 to 102%. To assess the possibility of interference from spice volatiles, the procedure was applied to 17 different spice oleoresins from 3 different manufacturers. No interferences were found, but methylene chloride levels up to 83 ppm and ethylene dichloride levels up to 23 ppm were detected. Trichloroethylene was not detected in any of the oleoresins.     

High-speed liquid chromatographic determination of monensin, narasin, and salinomycin in feeds, using post-column derivatization

A high-speed liquid chromatographic (LC) method using post-column derivatization is described for the determination of monensin, narasin, and salinomycin in a variety of animal feeds. The ionophores are extracted with hexane-ethyl acetate (90 + 10). A portion of the sample is evaporated, diluted to a known volume, and analyzed using a 6 cm 3 microns C18 column and an absorbance detector after post-column reaction with vanillin. The method has been applied to poultry and swine feeds with levels of 3-100 ppm added antibiotic. A comparison was also carried out with medicated poultry feed and beef feed lot supplement samples previously analyzed by 2 separate bioassay methods for monensin and salinomycin, respectively. Recoveries for the LC method ranged from 92.1 to 103% with an average recovery of 98.1% and a coefficient of variation of 3.65%.     

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.     

Gas-liquid chromatographic determination of pentachlorophenol in milk

A gas-liquid chromatographic (GLC) method developed by other workers for determining pentachlorophenol (PCP) in water has been adapted for determining PCP in raw and homogenized milk. PCP is extracted from milk with benzene and from the benzene into a potassium carbonate solution. Acetic anhydride is added to the aqueous solution to form PCP acetate, which is extracted into hexane and then determined by electron capture GLC. Duplicate determinations of PCP in milk fortified at levels of 0.02, 0.2, and 2.0 ppm gave respective average recoveries of 80.0, 87.2, and 85.0%. PCP levels as low as 0.005 ppm can be detected in 20 g milk.     

High pressure liquid chromatographic determination of polynuclear aromatic hydrocarbons in oysters.

A high pressure liquid chromatographic (HPLC) procedure is described for determining 13 polynuclear aromatic hydrocarbon (PNA) compounds in oysters at the 2 ppb level. These compounds are extracted from shellfish with acetonitrile and partitioned into petroleum ether; the petroleum ether is removed and the residue is saponified. The aromatic compounds are isolated by passing the saponifeid residue through silica gel and further purified and fractionated by muStyragel gel permeation chromatography. The in-ividual PNAs are then quantitatively determined by using a reverse phase HPLC column coupled to fluorescence, spectrophotometric, and 254 nm absorbance detectors in series. Recoveries from spiked samples generally were greater than 80%.