Minicolumn chromatography for the detection of sterigmatocystin in agricultural commodities

A simple method for detecting sterigmatocystin in agricultural commodities by minicolumn chromatography was developed. Clean-up as well as semi-quantitative estimation could be done on the same column. The method is suitable for the analysis of samples of rice, wheat, maize and sorghum contaminated with sterigmatocystin and could be used as an effective preliminary screening technique in public health laboratories.

Determination of sterigmatocystin in barley by acetylation and liquid chromatography

The estimation of sterigmatocystin by fluorescence liquid chromatographic analysis of the acetate derivative has eliminated the background interference normally encountered in analysis of underivatized sterigmatocystin in barley. Barley samples are extracted with acetonitrile-water; the extract is then washed with hexane, transferred to chloroform, and eluted from a silica gel column with cyclohexane-ethyl acetate. The extract is heated with pyridine and acetic anhydride for 3 h to give a stable derivative. Reverse-phase liquid chromatography, using a methanol-water mobile phase gradient and fluorescence detection, is the method of determination. Recoveries from barley samples spiked with 20, 110, 190, and 765 micrograms sterigmatocystin/kg were 31, 69, 75, and 96%, with coefficients of variation between 2.8 and 5.4%. Sterigmatocystin is confirmed by comparing retention times in underivatized extracts of samples and standards, using methanol-water (3 + 2) mobile phase and ultraviolet detection.

Chromatographic and spectroscopic properties of hemiacetals of aflatoxin and sterigmatocystin metabolites

Improved fluorescence detection of aflatoxin B1 by chromatographic analysis is accomplished by conversion to the corresponding hemiacetal, aflatoxin B2a. Because the metabolites aflatoxin M1, aflatoxin P1, aflatoxin Q1, sterigmatocystin, and O-methylsterigmatocystin have the same molecular conversion site, we investigated the chromatographic and spectroscopic properties of hemiacetals of these compounds to assist in confirming aflatoxins and sterigmatocystins in human urine. Nuclear magnetic resonance and infrared absorbance were used to confirm the hemiacetal structure for aflatoxin B1 and sterigmatocystin. The ultraviolet absorbance, fluorescence, and chromatographic properties of the metabolites were investigated. Using these data, we optimized the detection and solvent conditions for high-performance liquid chromatography. We determined that, of the conditions studied, maximum sensitivity and resolution for the native aflatoxins were achieved with a mobile phase of methanol, tetrahydrofuran, and water, a C8 column in series with a C18 column, and fluorescence detection with 365 nm excitation and 430 nm emission wavelengths for aflatoxins B1 and M1 and with 500 nm emission wavelength for aflatoxins P1 and Q1. For the analysis of the hemiacetals, a mobile phase of methanol, acetonitrile, and water provided better chromatography and fluorescence detection. Sterigmatocystin and O-methylsterigmatocystin were readily converted to the hemiacetal forms, which, like the aflatoxins, were more polar and, therefore, earlier eluting by reversed-phase HPLC (methanol, acetonitrile, and water, 236 nm absorbance). These data are important to maximize the sensitivity and confidence for detecting the mycotoxin metabolites in biological specimens.

Thin-layer chromatographic determination of sterigmatocystin in cheese: interlaboratory study

A collaborative study of a method for the determination of sterigmatocystin in cheese was conducted by 10 laboratories. The study included control samples and samples spiked at levels of 5, 10, and 25 ppb, in coded blind pairs. Recoveries were 60.0, 90.7, and 59.3%, outliers excluded, for the respective levels. The mean reproducibilities, outliers excluded, were 81.97, 17.13, and 52.77%, respectively. Mean repeatabilities, outliers excluded, were 77.66, 17.13, and 46.40%, respectively. Results of this collaborative study indicate that the method, modified as described in this report, is applicable to the determination of sterigmatocystin in cheese at low levels (5-50 ppb) for the purpose of surveys. With regard to the difficulty with thin-layer chromatography in this study, it is recommended that a more satisfactory determinative step be developed. Recommendation for official first action status is deferred.

An investigation of new commercial samples of methyl green and pyronin Y

New commercial samples of Methyl Green (Gurr Certistain), Pyronine G (Gurr Certistain) and Pyronin Y (Polysciences) have been investigated using spectrophotometry, thin layer chromatography and nuclear magnetic resonance, in addition to standardized simultaneous and sequential staining methods using purified Ethyl Green and pure Pyronin Y as reference dyes. The Methyl Green was found to be Ethyl Green contaminated with Crystal Violet. It did not have any advantages compared with Ethyl Green supplied by American dye companies. The Pyronine G sample was Pyronin Y with a high dye content that gave good staining results when used with purified Ethyl Green. Pyronin Y from Polysciences was found to be essentially pure Pyronin Y.

C. I. acid red 52: a new stain for cells of granulocytic origin

Using the xanthene dye C.I. acid red 52 (C.I. 45100) as a single agent stain applied to coverslip preparations of blood and bone marrow, primary and secondary granules in cells of neutrophilic origin stained brilliant pink. In eosinophils, granules stained dark red. In leukemic myeloblasts that also stained with Sudan black B and demonstrated myeloperoxidase and specific esterase activity, a few bright red staining granules were visualized with acid red 52. In some leukemic promyelocytes, Auer rods stained bright red. In leukemic lymphoblasts, no red granules were seen. Of a wide variety of dyes tested so far, acid red 52 is the most sensitive stain for primary and secondary granules of granulocytes in blood and bone marrow.

High-performance liquid chromatographic quantitation of rhodamines 123 and 110 from tissues and cultured cells

Rhodamine 123 is a fluorescent vital dye which has potential for therapeutic use in cancer treatment. The dye concentrates in mitochondria of normal and neoplastic cells but accumulates in and is toxic to neoplastic cells. When dye-treated cells are irradiated with blue laser light at 514 nm, mitochondrial injury or cell death results. Rhodamine concentration in cultured cells and tumor tissue was quantitated to correlate cell or tumor death with drug dose. A reversed-phase separation of rhodamine 123 was accomplished using a gradient of 0.05 M phosphate buffer pH 2.85 (mobile phase A) and acetonitrile (mobile phase B), 10-80% B in 15 min with a DuPont Golden Series C8 column. Effluent was monitored with a fluorescence detector at 295 nm excitation and 520 nm emission. Stock rhodamine 123 contained approximately 6-8% of rhodamine 110, the parent compound, which eluted at 9.8 min whereas rhodamine 123 eluted at 11.7 min. Structural verification of both compounds by field desorption mass spectrometry was performed. This is the first report of the chemical separation and quantitation of rhodamine 123 from cultured tumor cells or tumor tissue.

Enzyme-linked immunosorbent assay for secalonic acid D

A competitive enzyme-linked immunosorbent assay was developed for the xanthone dimer secalonic acid D. The immunogen and enzyme marker were prepared by direct reaction of secalonic acid D with bovine serum albumin and horseradish peroxidase, respectively. The resultant conjugates were characterized by UV/VIS spectra and thin layer chromatography. The hapten:protein ratios in the conjugates were estimated by difference UV/VIS spectra and by fluorescent techniques. Immunization procedures were conducted utilizing New Zealand rabbits over a period of 12 weeks. The competitive enzyme-linked immunosorbent assay on microtiter plates showed that secalonic acid D was detectable within a range of 250-25 000 ng/assay.

Thin layer chromatographic determination of sterigmatocystin in cheese

A one-dimensional thin layer chromatographic method has been developed for determining sterigmatocystin in cheese. Cheese is extracted with acetonitrile-4% KCl (85 + 15). A simplified liquid-liquid partition cleanup is used, and the sample extract is passed through a cupric carbonate column for final purification. Sterigmatocystin is visualized by spraying the plate with aluminum chloride. The fluorescence of the spot is enhanced 10-fold by additional plate spraying with a silicone-ether mixture, enabling sterigmatocystin detection and quantitation at 2 and 5 micrograms/kg, respectively. Average recoveries were 88.3 and 86.4% at the 10 and 25 micrograms/kg levels, respectively.

Sterigmatocystin in dairy cattle feed contaminated with Aspergillus versicolor

Sterigmatocystin (7.75 micrograms/g of feed) and a high-propagule-density of Aspergillus versicolor were detected in feed associated with acute clinical symptoms of bloody diarrhea and death in dairy cattle. Nine isolates of A. versicolor from the feed produced 13 to 89 micrograms of sterigmatocystin per g on cracked corn and lower amounts in liquid culture. This is the first report of sterigmatocystin in dairy cattle feed in the United States.

[Use of a colorimetric method employing rhodamine 6G for determining the free fatty acid content in biological membranes]

An improved modification of the Anderson-Chakrabarty method for demonstration of free fatty acids in the membranes of enterocytes, erythrocytes and mitochondrial fractions is described. The method includes the use of rhodamine 6G as a stain.

Mycotoxins in grain dust: method for analysis of aflatoxins, ochratoxin A, zearalenone, vomitoxin, and secalonic acid D

A multimycotoxin method is presented to quantitate aflatoxins, ochratoxin A, zearalenone, secalonic acid D, and vomitoxin in grain dust. Dust spiked with these mycotoxins was extracted sequentially with methylene chloride followed by acetonitrile-water (86 + 14). Vomitoxin was recovered in the latter extract and all other mycotoxins were recovered in the methylene chloride. Aflatoxins and ochratoxin were quantitated by fluorescence measurement on silica thin layer chromatographic plates. The other mycotoxins were quantitated after cleanup by reverse phase liquid chromatography and ultraviolet detection. Recoveries from dust spiked in the parts per billion (ng/g) range were approximately 80% (SD = 15-29%) for all mycotoxins. Minimum detectable amounts ranged from less than 0.5 ng/g for aflatoxins to 20 ng/g for zearalenone.

Two sites of intracellular localization of rhodaminyl-phalloidin in hepatocytes

The uptake of a fluorescent phallotoxin (tetramethylrhodaminyl-phalloidin) into rat hepatocytes has been studied. The experiments were performed in vitro, using freshly isolated hepatocyte suspensions or monolayers of hepatocytes cultured for up to 5 days, as well as in vivo, by investigating cryostat sections of a liver from an animal injected with the labelled toxin. In vitro, in freshly isolated hepatocytes, a staining of actin was observed. On the contrary, if the hepatocytes were cultured, only fluorescent endocytotic vesicles were found accumulated around the nucleus, and remaining in the cells unchanged for several days. In vivo, both fluorescent patterns were observed, often in one and the same cell. The endocytotic vesicles of rhodaminylphalloidin looked very similar to those obtained with fluoresceinyl-concanavalin A. navalin A. We conclude that in all systems the fluorescent phallotoxin enters the hepatocytes by endocytosis. However, in the freshly isolated cells the endocytotic vesicles apparently undergo some kind of processing with release of the toxin and subsequent staining of cellular actin, while in cultured hepatocytes the endocytotic vesicles persist unprocessed.

Spectrophotometric characteristics and assay of pure pyronin Y

The spectrophotometric characteristics of analytically pure pyronin Y have been investigated. Addition of metal ions (Fe3+, Zn2+, and Mg2+) and of dextrin were shown not to influence the absorption characteristics. The composition of the solvent strongly influenced the value of the extinction coefficient. Aqueous ethanolic solutions with a content of about 50% ethanol gave higher epsilon-values than those found for more concentrated ethanol solutions. The difference can be explained by the existence of a solvent-solute complex in the less concentrated ethanol solutions. A new spectrophotometric assay is proposed using the epsilon-value 11.7 X 10(4) lmol-1 cm-1 found in aqueous ethanol (52%) as standard.

[Study of the presence of sterigmatocystin in Czechoslovak grain]

Owing to its carcinogenic, hepatotoxic, nephrotoxic and dermatotoxic action, sterigmatocystine belongs to risky substances. Grains should be therefore examined for its content. A detailed description of a simple method for a current examination of grains for sterigmatocystine content is given and the method is recommended. Seventy-four samples were examined (24 samples of wheat, 19 samples of barley, 16 samples of maize, 10 samples of oats and 5 samples of rye) coming from the South Moravian, West Slovakian and East Slovakian regions from the 1980 and 1981 harvests. Only two barley samples and two maize samples were found to be positive: the maize samples contained about 50 micrograms and the samples of barley 200 and 400 micrograms of sterigmatocystine per 1 kg. One sample of wheat had a trace amount of the substance.

Attogram detection limit for aqueous dye samples by laser-induced fluorescence

A modified flow cytometer has been used to detect attogram quantities of aqueous rhodamine 6G by laser-induced fluorescence analysis. A detection limit of 28 attograms (35,000 molecules) was obtained, nearly two orders of magnitude better than earlier measurements. The detection limit in concentration units was 1.4 x 10(-13) mole per liter. During the 1-second measurement period, the total volume sampled was 0.42 microliter. On average, only half a rhodamine 6G molecule was present in the 6-picoliter probed volume.

[Study of cheeses for the presence of sterigmatocystin]

Sixty-six samples of hard cheeses (Edam Block, Edam Cake, Svĕtlan, Moravian Block, Emmenthal), taken from retail shops, were examined by the chromatographic method using thin silica-gel layer. Three samples were positive. It was demonstrated by semiquantitative examination that two samples of Edam Cake contained 7.5 and 17.5 micrograms of sterigmatocystine in kg and one sample of Moravian Block contained 7.5 micrograms/kg. The described method is very simple and is recommended to be used by food-control institutions for the practical examination of cheese for the presence of sterigmatocystine.

High-performance liquid chromatographic analysis of the mycotoxin secalonic acid D and its application to biological fluids

Secalonic acid D (SAD) is an acutely toxic, teratogenic and possibly mutagenic fungal metabolite produced in corn by Penicillium oxalicum. Using ultraviolet absorbance at 340 nm as a means of detection, SAD was resolved as a sharp peak by reversed-phase high-performance liquid chromatography (HPLC) on a small particle (10 mu m) mu Bondapak C18 column in 4 min by an acetonitrile--water--glacial acetic acid-tetrahydrofuran (5:3:0.5:0.5 for solvent system A and 4:3:0.5:0.5 for solvent system B) elution solvent system. The flow-rates for the two solvent systems (A and B) were 1.5 and 1.7 ml/min; column operating pressures of 1500 and 1800 p.s.i., respectively, resulted. The relationship between peak height or peak area and the quantity of SAD injected was linear over a range of 1--50 ng. Detection was very sensitive with lower limits of detection of 0.6 and 0.7 ng of SAD in solvent systems A and B, respectively. Retention times, peak heights and peak areas were highly reproducible in both solvent systems. Detection of SAD in spiked (0.2--10 mu g/ml) urine and bile samples injected without cleanup onto the HPLC column and quantitative extraction of SAD by ethyl acetate from spiked, acidified plasma samples (0.1--5 mu g/ml) followed by HPLC analysis were obtained. Solvent system B gave better resolution of SAD from the interfering substances in bile and urine than solvent system A. However, sensitivity was slightly greater in solvent system A.

Thin layer chromatographic method for analysis and chemical confirmation of sterigmatocystin in cheese

A semi-quantitative method is described for the analysis of sterigmatocystin in cheese. The method is based on extraction of cheese with MeOH--4% KCl (9 + 1), followed by Florisil and polyamide column cleanup and 2-dimensional thin layer chromatography (TLC). Visualization of sterigmatocystin on the TLC plates is enhanced by an AlCl3 spray reagent. The identity of sterigmatocystin is confirmed by a 2-dimensional TLC test based on reaction with trifluoroacetic acid (TFA) on the plate after first development. The reaction product formed is visualized by spraying with AlCl3. The method allows detection and confirmation of sterigmatocystin in cheese at concentrations as low as 5 micrograms/kg. The method has been applied to cheese samples ripening in warehouses and naturally molded with Aspergillus versicolor.