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The metabolism of dimethylarsinic acid (DMA) a common pesticide and the main metabolite of inorganic arsenic in mammals, has been studied in mice, hamsters and man. Mice and hamsters were administered a single dose of 74As-DMA (40 mg As/kg body weight) orally, while a human subject ingested DMA corresponding to 0.1 mg As/kg body weight. Ion exchange chromatography, paper electrophoresis, thin layer chromatography as well as arsine generation--gas chromatography combined with atomic absorption spectrophotometry or mass spectrometry were used to characterize the arsenic metabolites in urine and feces collected over 48 hours after treatment. In mice and hamsters 3.5% and 6.4% of the dose, respectively, were excreted in urine in the form of trimethylarsine oxide (TMAO). No TMAO was found in feces. A DMA-complex was detected in urine and feces. It amounted to about 13% of the dose in mice and 15% in hamsters. About 80-85% of the dose was eliminated in urine and feces in the form of unmetabolized DMA. No demethylation of DMA to inorganic arsenic was observed. In man, about 4% of the dose was excreted in urine as TMAO and about 80% as DMA.

All retinol derivatives saturated at the terminal oxygen (methyl retinyl ether, retinol, retinyl acetate, and retinyl palmitate) tended to form anhydro retinol upon exposure to hot columns and metal tubing. A free radical-induced dehydration of this group of compounds is favored over the well known acid catalyzed reaction on the following grounds: Injection of NH3 or pyridine, which should neutralize acidic sites, did not decrease the dehydration. The relative rates of dehydration in acid media are retinol > methyl retinyl ether > retinyl acetate (3). During gas chromatography, the relative rates are essentially invertede.g., retinyl acetate > retinol > methyl retinyl ether. Hydroquinone, a free radical inhibitor, decreased dehydration in columns packed with glass beads.Further study of the mechanism by which /3-carotene and hydroquinone inhibit the dehydration reactions would be welcome and might lead to the introduction of other suitable protective agents for retinol and other unstable compounds.The dehydration reaction has been used in liquid medium as an assay procedure for free retinol (4). Similarly, the formation of anhydro retinol during gas chromatography could be used as an assay for retinol, its ethers, and its esters if the procedure were carried out under conditions conducive to dehydration-i.e., high column temperatures and long retention times. This assay might be particularly applicable to the natural esters of retinol, which cannot be chromatographed without destruction at this time.LITERATURE CITED(1) Commission on Nomenclature of Biological Chemistry, International Union of Pure and Applied Chemistry, J. Am.Chem. Soc. 82, 5575 (1960).

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