Speciation of Dimethylarsinous Acid and Trimethylarsine Oxide in Urine from Rats Fed with Dimethylarsinic Acid and Dimercaptopropane Sulfonate

Speciation of arsenic in urine from rats treated with dimethylarsinic acid (DMA^V) alone or in combination with dimercaptopropane sulfonate (DMPS) were studied. Methods were developed for the determination of the methylarsenic metabolites, especially trace levels of dimethylarsinous acid (DMA^III) and trimethylarsine oxide (TMAO), in the presence of a large excess of DMA^V. Success was achieved by using improved ion-exchange chromatographic separation combined with hydride generation atomic fluorescence detection. Micromolar concentrations of DMA^III were detected in urine of rats fed with a diet supplemented with either 100 μg/g of DMA^V or a mixture of 100 μg/g of DMA^V and 5600 μg/g of DMPS. No significant difference in the DMA^III concentration was observed between the two groups; however, there was a significant difference in TMAO concentrations. Urine from rats fed with the diet supplemented with DMA^V alone contained 73 ± 30 μM TMAO, whereas urine from rats fed with the diet supplemented with both DMA ^V and DMPS contained only 2.8 ± 1.4 μM TMAO. Solutions containing mixtures of 100 μg/L DMA^V or TMAO and 5600 μg/L DMPS did not show reduction of DMA^V and TMAO. The significant decrease (p < 0.001) of the TMAO concentration in rats administered with both DMA^V and DMPS suggests that DMPS inhibits the biomethylation of arsenic.