Review of in vitro test systems using DNA damage and repair for screening of chemical carcinogens.

Chemical carcinogens are mechanistically classified as genotoxic which interact directly with DNA, and epigenetic which cause chronic tissue injury, hormonal imbalance, and promotional effects. This review evaluates in vitro tests for their contribution to a battery for identifying genotoxic chemical carcinogens. In addition to bacterial mutagenic assays, nonspecific DNA damage/repair tests are recommended for screening chemicals, in particular the hepatocyte primary culture/DNA repair test.     

Colorimetric determination of poly(N-vinyl-2-pyrrolidone) in contact lens solutions.

A rapid colorimetric method is presented for the quantitative determination of poly(N-vinyl-2-pyrrolidone) in contact lens solutions. The method is simple, requires no sample pretreatment, and uses only a small volume of sample. The procedure is based on the measurement of the net absorbance of a poly(N-vinyl-2-pyrrolidone)- Congo red complex at 545 nm. An accuracy of greater than +/- 4% was obtained for the concetnration ranges usually found in contact lens solutions with a minimum detection level of 10 ppm. The method is useful as a screening procedure for solutions of unknown composition and as a quality assurance procedure for routine determinations.     

Spectrophotometric analysis of binary mixtures of sulfonamides.

Different methods for analyzing binary mixtures by using 2 wavelengths are reviewed. The absorbance ratio calculated at 2 wavelengths, not including the isoabsorptive point, was a quadratic function of relative concentration. The curve-fitting process using orthogonal polynomials was applied to obtain the quadratic equation. An absorbance ratio can be used as a rapid purity index for sulfacetamide sodium in the presence of sulfanilamide. Sulfacetamide sodium has been determined in eye drop preparations.     

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.     

Analysis of foods for iodine: interlaboratory study

An accurate, reproducible method for less than or equal to 1 ppm iodine in foods is required for nutritional labeling. In order to ascertain the current status of iodine analysis in foods, 7 samples, representing different food classes, were analyzed by 8 laboratories. Six laboratories used their modifications of the Ce-As-I catalytic method preceded by alkaline dry ashing. Two laboratories used neutron activation analysis (NAA), with differing radiochemical separations. The study showed wide discrepancy in analytical results. Mean relative standard deviation for all laboratories was 77.9% between laboratories; 19.1% within-laboratories. Laboratories using NAA had only slightly better precision than did laboratories using the chemical method. The lowest level reported on the entire group of samples ranged among laboratories from 0.0089 to 0.65 ppm. Figures reported by a laboratory are, in general, consistently high or consistently low. The only differences in methodology which may possibly correlate with level of iodine obtained are the use of NAA technique and use of manual, rather than automated, colorimetry.     

Extraction, cleanup, and quantitative determination of aflatoxins B1 ANd M1 in beef liver

A method for the determination of aflatoxin B1 in eggs was applicable for aflatoxin B1 in liver, but ineffective for aflatoxin M1 in liver because of poor recovery of added aflatoxin and interferences in thin layer chromatography. The method was modified by the addition of citric acid to the extracting solvent and ammonium sulfate to the extract solution for removing protein. The elution system for silica gel column cleanup was also changed by substituting methanol for acetone, and adding a step for confirmation of aflatoxin M1 identity. The method has been used successfully for survey and research on aflatoxin residues in animal tissues.