Gas chromatographic determination of deoxynivalenol in wheat

Modifications to a published method are described for the determination of deoxynivalenol (DON) in wheat by gas chromatography with electron capture quantitation of the heptafluorobutyrate derivative. In the modified method, DON is extracted by shaking the sample with methanol-water on a wrist-action shaker, followed by filtration through rapid flow paper. One concentration step is eliminated, and a hexane wash is incorporated to remove toluene from the silica gel column. Recoveries of DON from wheat samples spiked at 0.1, 0.5, and 1.0 ppm ranged from 77.3 to 86.3% and averaged 81.5%.     

Gas chromatographic method for determination of chlorpyrifos and its metabolite 3,5,6-trichloro-2-pyridinol (TCP) in dates.

A method is described for the determination of the insecticide chlorpyrifos and its metabolite TCP in green, unprocessed, and processed dates with the seeds incorporated. After extraction, chloropyrifos is cleaned up using Florisil and analyzed using a gas chromatography (GC) equipped with a nitrogen/phosphorus detector. TCP is derivatized using bis-(trimethylsilyl)-acetamide (BSA) to form the TCP-derivative and analyzed by a gas chromatograph equipped with a Hall electrolytic conductivity detector. Recoveries of chlorpyrifos from all fortified dates (0.05 and 0.1 ppm) ranged from 86 to 110% with an average of 94.5%. Recoveries of TCP from all fortified dates (0.1 and 0.2 ppm) ranged from 79 to 99% with an average of 86%. Limits of detection for chlorpyrifos and TCP in green, unprocessed, and processed dates were 0.02 and 0.05 ppm, respectively.     

Gas chromatographic determination of deoxynivalenol in wheat with electron capture detection: collaborative study

Ten laboratories participated in a collaborative study of a method for the determination of deoxynivalenol in wheat by gas chromatography with electron capture detection. Each laboratory analyzed 6 samples in duplicate. Each collaborator received samples spiked at the 100.3, 501.3, and 1002.6 ng/g levels; a control sample; and 2 naturally contaminated samples. The average recovery (outliers excluded) for the spiked samples was 92.2%. The mean repeatability and reproducibility, respectively, were 32.2 and 41.3% for the spiked samples and 30.9 and 47.6% for the naturally contaminated samples. The method was adopted official first action.     

Gas chromatographic screening method for T-2 toxin, diacetoxyscirpenol, deoxynivalenol, and related trichothecenes in feeds

A gas chromatographic method for screening trichothecene mycotoxins in feeds is described. Feed is extracted with acetonitrile-water, and the toxins are purified with charcoal-alumina-Celite, Florisil, and silica mini-columns. Deoxynivalenol (DON), nivalenol (NIV), diacetoxyscirpenol (DAS), T-2 toxin, and their fungal metabolites are hydrolyzed to their corresponding parent alcohols (DON, NIV, scirpentriol, or T-2 tetraol) by alkaline hydrolysis. After derivatization to their pentafluoropropionyl analogs, they are quantitated by capillary gas chromatography with electron capture detection. Identity can be confirmed and sensitivity can be increased by using negative chemical ionization mass spectrometry with no additional sample workup. Recoveries of DAS, DON, and T-2 toxin averaged, respectively, 80, 65, and 85% in corn; 84, 65, and 88% in soybeans; and 70, 57, and 96% in mixed feeds at concentrations ranging from 0.1 to 2.0 ppm. Recoveries of 15-monoacetoxyscirpenol (MAS), HT-2, NIV, and T-2 tetraol were 97, 97, 86, and 56%, respectively, in corn at a concentration of 0.25 ppm: A detection limit of 0.02 ppm in corn, soybeans, and mixed feeds, and 0.05 ppm in silages is estimated.     

Comparison of Carr-Price analysis and liquid chromatographic analysis for vitamin A in fortified milk

The determination of the vitamin A concentration in fortified milk was compared using Carr-Price analysis and liquid chromatography (LC). Carr-Price analysis required saponification of the sample with alcoholic potassium hydroxide, extraction with ether, and colorimetry with antimony trichloride in chloroform. LC analysis required hexane extraction of a 71% alcohol-sample solution and centrifugation at 2000 rpm. A 100 microL aliquot of the extract was analyzed on a LiChrosorb Si-60, 5 micron column, using an ethyl ether-hexane (2 + 98) mobile phase and detection at 313 nm. Each method was statistically evaluated for precision and sample-to-sample reproducibility. The LC extraction procedure was examined for efficiency. Each LC value was divided by the Carr-Price value obtained for the same sample; an average value of 0.975 with a coefficient of variation of 6.90% was obtained. It was concluded that the procedures were statistically equivalent.     

Nonaqueous reverse phase liquid chromatographic analysis for cholesterol in milk chocolate

A method using liquid chromatography was developed for the analysis of cholesterol in milk chocolate products. The method involves saponification of the sample with methanolic KOH followed by extraction with ether. Potentially interfering components are eliminated through the use of a silica Sep-Pak cleanup step before injection. The nonaqueous reverse phase LC system consists of a C18 column and an isopropanol-hexane mobile phase with direct detection at 205 nm. Recoveries of 1, 3, and 5 mg cholesterol added to 1 g sample of milk chocolate were 88.6, 102.8, and 110.1%, respectively. Studies conducted with [4-14C]-cholesterol were undertaken to further document the accuracy of the method.     

Gas chromatographic organic acid profiling analysis of brandies and whiskeys for pattern recognition analysis

An efficient gas chromatographic profiling and pattern recognition method is described for brandy and whiskey samples according to their organic acid contents. It involves solid-phase extraction of organic acids using Chromosorb P with subsequent conversion to stable tert-butyldimethylsilyl derivatives for the direct analysis by capillary column gas chromatography and gas chromatography-mass spectrometry. A total of 12 organic acids were reproducibly identified in liquor samples (1 mL). When the GC profiles were simplified to their retention index spectra, characteristic patterns were obtained for each liquor sample as well as for each group average. Stepwise discriminant analysis provided star symbols characteristic for each liquor sample and group average. As expected, canonical discriminant analysis correctly classified 23 liquor samples studied into two groups of either brandy or whiskey.     

Liquid chromatographic determination of aflatoxin M1 in milk

The official AOAC method for aflatoxin M1 in milk was modified by replacing cellulose column chromatography with cartridge chromatographic cleanup and replacing thin layer chromatographic (TLC) determination with liquid chromatographic (LC) quantitation to yield a new method for bovine and porcine milk. An acetone extract of milk is treated with lead acetate and defatted with hexane, and M1 is partitioned into chloroform as in the AOAC method. Chloroform is removed by evaporation under a stream of nitrogen at 50 degrees C. The residue is dissolved in chloroform, the vessel is rinsed with hexane, and the 2 solutions are applied in sequence to a hexane-activated silica Sep-Pak cartridge. Less polar impurities are removed with hexane-ethyl ether, and M1 is eluted with chloroform-methanol, and determined by C18 reverse phase LC using fluorescence detection. Recoveries of M1 added to bovine milk at 0.25, 0.50, and 1.0 ng/mL were 90.8, 93.4, and 94.1%, respectively. The limit of detection was less than 0.1 ng M1/mL for both bovine and porcine milk.     

Improved cleanup for liquid chromatographic analysis and fluorescence detection of aflatoxins M1 and M2 in fluid milk products

A rapid method is described for extraction and cleanup of raw and processed milk for determination of aflatoxins M1 and M2 by using a C18 Sep-Pak/silica gel cleanup column combination. Aflatoxins are separated by normal phase liquid chromatography and their concentrations are determined by fluorescence detection in a silica gel-packed flow cell. Recoveries ranged from 99 to 103% with coefficients of variation less than 2% for M1 levels of 0.117-1.17 ng/mL added to raw milk. Similar recoveries were obtained for M2. The coefficient of variation for analysis of 5 subsamples of naturally contaminated milk was less than 1%. Agreement with the official method is satisfactory. Each sample requires less than 25 mL solvent and 10 min actual handling time. Sample chromatograms show no interferences in the M1-M2 elution region and no late-eluting peaks, which permits spacing injections at 13-20 min intervals. Aflatoxin levels as low as 0.03 ppb may be determined by this procedure. Extracts have also been analyzed by thin layer chromatography.     

Liquid chromatographic determination of fluridone aquatic herbicide and its metabolite in fish and crayfish

A residue method is described for determination of the aquatic herbicide fluridone (1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4(1H)-pyridinone) and its metabolite (1-methyl-3-(4-hydroxyphenyl)-5-[3-(trifluoromethyl) phenyl]-4(1H)-pyridinone) in fish and crayfish tissues. Both compounds are extracted from tissues with methanol, and the extracts are subjected to acidic hydrolysis to release conjugated forms of fluridone and the metabolite. Sample extracts are purified by liquid-liquid partitioning and Florisil Sep-Pak column chromatography. Both compounds are separated and measured by reverse phase liquid chromatography with UV detection at 313 nm. In the absence of interfering peaks, the method has a detection limit of approximately 0.04 ppm of either compound. Overall, recoveries averaged 96% for fluridone and 78% for the metabolite for all tissue types combined.     

Rapid high pressure liquid chromatographic determination of aflatoxin M1 in milk and nonfat dry milk

A modification of the current revised AOAC method, 26.A10-26.A15, is described for the rapid analysis of aflatoxin M1 in milk and nonfat dry milk. The method incorporates chloroform extraction and eliminates the need for column chromatography by using liquid-liquid partition for sample extract cleanup. Quantitation is carried out by using fluorescence detection combined with high pressure liquid chromatography (HPLC) of aflatoxin M1 which has been converted to aflatoxin M2a with trifluoroacetic acid. The method has a detection limit of 0.014 micrograms/L (2 X signal/noise) for whole milk. For 6 samples of naturally contaminated nonfat dry and freeze-dried milk, the modified method gave an average result of 0.698 micrograms/L; the AOAC method gave an average result of 0.386 micrograms/L.     

Thin layer chromatographic determination of deoxynivalenol in processed grain products

The thin layer chromatographic (TLC) method of Trucksess et al. (J. Assoc. Off. Anal. Chem. (1984) 67, 40-43) was modified for the determination of deoxynivalenol (DON) in high-sugar breakfast cereals, corn syrup, and beer. Celite was added to the substrate before extraction with acetonitrile-water (84 + 16). After filtration through an alumina-charcoal-Celite (0.5 + 0.7 + 0.3) column, the filtrate was evaporated to dryness and redissolved in water, which was passed through an octylsilyl reverse phase column. DON was eluted with anhydrous ethyl ether. The residue remaining after the eluate was evaporated to dryness was dissolved in CHCl3-acetonitrile (4 + 1) and chromatographed on AlCl3-impregnated silica gel TLC plates. The blue fluorescent DON spot was quantitated fluorodensitometrically after the TLC plate was heated at 120 degrees C for 7 min. Recoveries of DON added to breakfast cereals at 100, 200, and 400 ng/g levels and to syrup and beer at 50, 100, and 200 ng/g levels averaged 86%. The limit of determination in these products was about 50 ng/g.     

Gas chromatographic analysis of total fatty acids in cider

This paper reports the composition of total fatty acids in an apple beverage, cider. Fatty acids are present in the free or esterified form and contribute to both the flavor and foam properties of cider. Fatty acids were separated and identified as methyl esters by GC-MS, and 12 of these were subsequently determined by GC-FID. The major fatty acids found in cider were caproic, caprylic, capric, and palmitic acid, the saturated acids predominating over the unsaturated ones. The proposed method was applied to 59 ciders from three consecutive harvests (1996, 1997, and 1998), which were made by 19 cider-makers from the region of Asturias (Spain). Linear discriminant analysis of fatty acids in these samples allowed selection of palmitoleic, pentadecanoic, linoleic, myristic, and linolenic acid as the most predictive variables to differentiate ciders made from apples grown in the Asturias region (1997 harvest) and ciders made from apples grown outside this region (1996 and 1998 harvests).     

Thin layer chromatographic method for determination of deoxynivalenol in wheat: collaborative study

A collaborative study of a rapid method for the determination of deoxynivalenol (DON) in winter wheat was successfully completed. The method involves sample extraction with acetonitrile-water (84 + 16), cleanup using a disposable column of charcoal, Celite, and alumina, and detection by thin layer chromatography after spraying with an aluminum chloride solution. Each of the 15 collaborators analyzed 12 samples, 2 of which were naturally contaminated, and 10 to which DON was added, in duplicate, at levels of 0, 50, 100, 300, and 1000 ng/g. Average recoveries of DON ranged from 78 to 96% with repeatabilities of 30-64% and reproducibilities of 33-87%. The results of the study show that false positives were not a problem and that all of the analysts could detect DON at the 300 ng/g level or higher. The method has been adopted official first action.     

Liquid chromatographic monitoring of the depletion of carbadox and its metabolite desoxycarbadox in swine tissues

A liquid chromatographic method was used to monitor a depletion study of carbadox (and its most important metabolite, desoxycarbadox) in young pigs fed carbadox-treated rations for 1 week. Carbadox was found in blood (20 ppb), blood serum (26 ppb), and muscle tissue 24 h after withdrawal from treated ration; residues were reduced to a trace (less than 2 ppb) in 48 h, and eliminated by 72 h. Desoxycarbadox, although not detected in blood, was found in muscle (17 ppb) 24 h after withdrawal; it was reduced to 9 ppb at 48 h and to a trace by 72 h. Although no carbadox was detected in liver 24 h after withdrawal, appreciable desoxycarbadox (125 ppb) was found in liver 24 h after withdrawal; it was reduced to 17 ppb at 48 h and to a trace by 72 h. Whereas only a trace of carbadox was found in kidney 24 h after withdrawal, 186 ppb desoxycarbadox was found in kidney at 24 h, 34 ppb at 48 h, and a trace at 72 h. No metabolite of carbadox other than desoxycarbadox was found in extracts of swine tissues during this medicated feed trial, and no metabolite was found in blood extracts by using the established methodology. The effect of tissue storage (aging) at -20 degrees C on levels of the drug and its metabolite was a modest alteration of residue levels. The inadvertent use of feed adulterated with furazolidone and initially medicated with chlortetracycline, sulfamethazine, and penicillin G, did not affect the uptake of carbadox in this depletion study or interfere with the analytical methodology.