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 dimethyl-arsinous acid (DMA(III)) and trimethylarsine oxide (TMAO), in the presence of a large excess of DMAV. Success was achieved by using improved ion-exchange chromatographic separation combined with hydride generation atomic fluorescence detection. Micromolar concentrations of DMAIII were detected in urine of rats fed with a diet supplemented with either 100 mug/g of DMA(V) or a mixture of 100 mug/g of DMA(V) and 5600 mug/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 muM TMAO, whereas urine from rats fed with the diet supplemented with both DMA(V) and DMPS contained only 2.8 +/- 1.4 muM TMAO. Solutions containing mixtures of 100 mug/L DMA(V) or TMAO and 5600 mug/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.