Rapid quantitative thin layer chromatographic screening procedure for sulfathiazole residues in honey

A procedure is presented for the quantitative determination of sulfathiazole residues in honey. Induced fluorescence of sulfathiazole is measured by fluorescent scanning densitometry; sulfaquinoxaline is added as an internal standard for quantitation. Recovery is greater than 98% and results are linear over the range 0.05-0.60 mg/kg. The detection limit, CL (k = 3), is 0.02. The procedure allows a single analyst to process 50-60 samples/day.     

Quantitative thin layer chromatographic multi-sulfonamide screening procedure: collaborative study

A thin layer chromatographic procedure suitable for detection of multiple sulfonamides at 0.1 ppm was studied in an interlaboratory collaborative study. Sulfamethazine, sulfadimethoxine, and sulfaquinoxaline were variously analyzed in liver and muscle tissues from swine, turkey, and duck. The average recovery for all drugs across all tissues was 95%. The corresponding repeatability and reproducibility were 7.7% and 10.5%, respectively.     

Simultaneous extraction and fractionation and thin layer chromatographic determination of 14 mycotoxins in grains.

A simple, systematic analytical method for multiple mycotoxins was developed for detecting 14 mycotoxins; aflatoxins B1, B2, G1, and G2, sterigmatocystin, T-2 toxin, diacetoxyscirpenol, neosolaniol, fusarenon X, zearalenone, ochratoxin A, citrinin, luteoskyrin, and rugulosin. These mycotoxins were extracted with 20% H2SO4-4% KCl-acetonitrile (2 + 20 + 178), defatted with isooctane, and transferred to chloroform. The chloroform extract was cleaned up by silica gel column chromatography; the first 10 toxins were eluted with chloroform-methanol (97 + 3) and the remaining 4 toxins with benzene-acetone-acetic acid (75 + 20 + 5). Each fraction was analyzed by thin layer chromatography for the final determination. The method has been applied to polished rice, rough rice, corn, wheat, and peanuts as an analytical screening procedure. The detection limits in these commodities ranged from 10.00 to 800.0 microgram/kg, depending on the mycotoxin, but all limits were superior to those obtained for the individual mycotoxins by using other methods.     

Detection of twelve mycotoxins in mixed animal feedstuffs, using a novel membrane cleanup procedure.

A multimycotoxin thin layer chromatographic screening method is described which is applicable to most animal feedstuffs. Interference from nonspecific lipid, pigment, and other components of simple and mixed feeds is reduced to a minimum by using a membrane cleanup step. Aflatoxins B1, B2, G1, and G2, citrinin, diacetoxyscirpenol, ochratoxin A, patulin, penitrem A, sterigmatocystin, T-2 toxin, and zearalenone may be reliably detected. The sensitivity of the method is generally low for mixed feeds but even so aflatoxin B1 can be detected at a level of 3 ppb and ochratoxin A at 80 ppb. While the basic method is less sensitive for sterigmatocystin (330 ppb), patulin (600 ppb), zearalenone (1000 ppb), and the trichothecenes (1000-4000 ppb), it may be adapted so as to reduce the above detection limits when the presence of these toxins is suspected. Lower levels may be detected in extracts of simple feeds.     

Formation of aflatoxin derivatives on thin layer chromatographic plates.

Rapid confirmation of the presence of aflatoxins B-1 and G-1 in foods is provided by reaction with trifluoroacetic acid at the origin of a thin layer chromatographic plate. The procedure has been used successfully with various nuts, grains, coffee and cocoa beans, and other foods.     

Spectrofluorometric determination and thin layer chromatographic identification of tyramine in wine.

A method is described for determining tyramine in wine by sand column extraction in an alkaline medium with anhydrous sodium sulfate. Tyramine is identified and quantitated by spectrofluorometry after the final extract is reacted with alpha-nitroso-beta-naphthol; identity is confirmed by thin layer chromatography. The average recovery was 98.93%. The method is applied to samples of 3 different wines obtained throughout the vinification process. Tyramine, which was not present in the must, appears in considerable quantities 15 days after the vinification process has begun.     

Derivatization procedure for identification of aflatoxin M1 on a thin layer chromatogram.

A commodity extract containing presumptive aflatoxin M1 is placed on an origin spot of a thin layer chromatographic plate and overspotted with trifluoroacetic acid. The mixture is held in the dark 30 min at ambient temperature and then 30 min at 55 degrees C. The plate is developed with CHCL3-acetone-2-propanol (85+10+7). The Rf values of reacted and unreacted aflatoxin M1 are compared with authentic M1 similarly treated for identification. The lowest concentration that has been identified is 0.1 mug/kg.     

Simultaneous thin layer chromatographic determination of aflatoxin B1 and ochratoxin A in black olives

A screening method has been developed for simultaneous determination of aflatoxin B1 and ochratoxin A in black olives. The technique includes extraction of both mycotoxins with aqueous methanol, cleanup using lead acetate, defatting with hexane, partitioning in chloroform, and thin layer chromatography. Detection limits are 5-7 micrograms aflatoxin B1 and 20 micrograms ochratoxin A/kg.     

Neutral cleanup procedure for 2,3,7,8-tetrachlorodibenzo-p-dioxin residues in bovine fat and milk.

A neutral cleanup method for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in milk and animal tissue was developed involving solvent extraction and liquid adsorption chromatography on magnesia-Celite 545, alumina, and Florisil. Cleaned up extracts were subjected to dual-ion analysis in a direct probe high resolution mass spectrometer, interfaced to a multi-channel analyzer for signal averaging. Calibration experiments were carried out with bovine milk and beef fat samples containing added TCDD. The 37CI isotopic isomer of TCDD was added as an internal standard. The response was linear for concentrations in the ppt range, with recoveries about 80%. Milk from a cow fed TCDD was cleaned up by the neutral procedure or, alternatively, a base-acid extraction procedure. The TCDD recoveries for both procedures were essentially the same. Recoveries of TCDD from liver samples of a rat given 14C-TCDD intraperitoneally, subjected to neutral cleanup and radioactive counting, were about 70%.     

Rapid thin layer chromatographic method for determining aflatoxin B1, ochratoxin A, and zearalenone in corn

A multimycotoxin thin layer chromatographic method is described for the analysis of corn. Aflatoxins are extracted from the samples with acetonitrile-water, and sodium bicarbonate is added to separate the acidic ochratoxin from zearalenone and aflatoxin B1. After chloroform extraction, 1N NaOH is added to separate zearalenone and aflatoxin B1. The separated mycotoxins are spotted on TLC plates, which are then examined under ultraviolet light. The following recoveries (%) were obtained for corn samples: aflatoxin B1 71, ochratoxin A 87, and zearalenone 85. The limits of detection for the respective mycotoxins were 2, 40, and 200 ppb.     

Rapid thin layer chromatographic determination of aflatoxin M1 in powdered milk

A method has been developed for the detection of aflatoxin M1 in milk. The toxin is extracted with chloroform, the extract is evaporated, and the residue is partitioned between carbon tetrachloride and an aqueous saline-methanol solution. The toxin is once again extracted with chloroform from the methanol solution and analyzed by thin layer chromatography. The limit of detection of M1 in powdered milk is 0.5 microgram/kg; recoveries of added M1 are about 83%. The limit of detection can be improved to 0.3 microgram/kg if the plate is sprayed with an aqueous solution of H2SO4 after development.     

Improved spray reagent for thin layer chromatographic method for detecting uric acid: collaborative study

A collaborative study was conducted to validate the substitution of an improved single spray in the official AOAC thin layer chromatographic method for identifying uric acid (UA) from bird and insect excreta. The proposed reagent, which is a dilute aqueous solution of ferric chloride and potassium ferricyanide, requires neither a heating step nor a pH indicator. Its preparation time, specificity, and sensitivity to low levels (5-50 ng) of UA were compared with those of the official sprays. The improved spray took 1/5 as long to prepare as the official sprays. Neither the proposed spray nor the official sprays gave false positive reactions with compounds similar to UA. For bird and insect excreta samples, at the 95% confidence limits, the false negative rate was between 0 and 9.7% for the proposed spray and between 0.7 and 18.7% for the official sprays. Sensitivity results showed that the proportion positive for the proposed spray was significantly higher (P less than 0.05) than for the official sprays at the 15 ng UA level. The proposed changes have been adopted official first action.     

Sensitive thin layer chromatographic detection of high fructose corn sirup and other adulterants in honey.

A highly sensitive procedure has been developed to detect the undeclared addition of high fructose corn sirup (HFCS) to honey. Carbohydrates must be separated first to achieve the requisite degree of sensitivity; charcoal-Celite chromatography was used to isolate a fraction containing oligo- and polysaccharides. The fraction was then concentrated and examined by thin layer chromatography on silica gel. Pure honeys yielded only 1 or 2 blue-grey or blue-brown spots at Rf values greater than 0.35; a series of spots or blue streaks extending from the origin characterized adulterated samples. The method detects HFCS and conventional honey adulterants at levels as low as 10% or less of the total mixture. In addition, the procedure detects the presence in honey of all starch-derived sugar sirups tested thus far, regardless of the plant source.     

Zinc chloride-diphenylamine reagent for thin layer chromatographic detection of some organophosphorus and carbamate insecticides

Zinc chloride-diphenylamine reagent, whose use has been reported for the detection of organochlorine insecticides by thin layer chromatography, was further studied for its ability to detect the organophosphorus insecticides phorate, phosphamidon, DDVP, and phosalone and the carbamate insecticide carbaryl and aldicarb. These insecticides give intense blue-green spots with this reagent. The procedure can be applied to the detection of the insecticides in biological materials and thus has a potential use in forensic toxicology.     

A convenient wet digestion procedure for multielement analysis of plant materials

Abstract

For the determination of total element contents in plant material by atomic spectrometry after wet digestion, both dissolution and oxidation of the matrix are necessary. This was achieved by a sequential digestion procedure using first hydrogen fluoride (HF) for dissolution of silicate, followed by oxidation with nitric acid (HNO₃) and hydrogen peroxide (H₂O₂). The final solution is 0.2M HNO₃, and contains only traces of HF. Application of the method for the determination of aluminium (Al), boron (B), calcium (Ca), cadmium (Cd), copper (Cu), iron (Fe), potassium (K), magnesium (Mg), manganese (Mn), sodium (Na), phosphorus (P), lead (Pb), sulfur (S), and zinc (Zn) in various materials showed good agreement with certified reference materials.     

Thin layer chromatographic screening method for sulfadiazine residues in calf tissues, plasma, and urine

Because of the lack of specificity of the Bratton-Marshall procedure for assaying sulfonamides, a sensitive, specific tissue residue assay for sulfadiazine (SDZ) was developed. The methodology has been extended to provide a highly sensitive screen for sulfonamide residues, which employs 2-dimensional thin layer chromatography in conjunction with fluorescamine derivatization. The procedure described, which has been developed for SDZ in calf tissues, involves direct ethyl acetate extraction of tissue homogenates. Following evaporation of the organic phase, a portion of the residue is spotted on a 20 X 20 cm silica gel 60 plate, which is then developed in 2 dimensions with solvent systems devised to separate SDZ from endogenous substances as well as from 12 other sulfonamides that might be present in calf tissues. The presence of SDZ at a concentration of 0.1 ppm or its absence is easily demonstrated in calf kidney, liver, muscle, plasma, and urine. The basic method can be modified for a particular sulfonamide in a target tissue and can be used as a quantitative assay for sulfonamide residues.     

Rapid thin layer chromatographic determination of zearalenone in corn, sorghum, and wheat

A rapid method is described for determining zearalenone in corn, sorghum, and wheat. The mycotoxin is extracted with a mixture of acetonitrile and 4% KCl in HCl. The extract is cleaned up with isooctane, evaporated, and redissolved in chloroform. Zearalenone is separated by thin layer chromatography; identity is confirmed with various developing solvents and spray reagents. Zearalenone is then quantitated by the limit detection method. The minimum detectable concentration is 140-160 micrograms/kg when aluminum chloride solution is used as spray reagent, and 85-110 micrograms/kg when Fast Violet B salt is used as spray reagent.