Chris Le and colleagues have developed a technique that allows them to detect two previously unobserved intermediates in arsenic metabolism (Anal. Chem. 2000, 72, 5172–5177). These intermediate species are known to be highly toxic, more so than inorganic arsenic, and their presence calls into question the nullifying effects associated with arsenic methylation.

The toxic intermediates, which were isolated and spectroscopically identified from the urine samples, were monomethylarsonous acid (MMA^III) and dimethylarsinous acid (DMA^III). The separation method combined HPLC with hydride-generation atomic-fluorescence detection. The species were separated with ion-pair chromatography and then immediately converted to their respective hydride derivatives, each of which was in the gas phase. The gaseous hydrides were then isolated from the solution of byproducts and detected by atomic fluorescence. This gas–liquid separation allowed for high sensitivity because it eliminated sample matrix interference.

The sensitivity and efficiency of the new technique should have major effects on the studies of trends in arsenic levels in populations. The group plans to perform further analyses on the MMA^III and DMA^III found in urine samples. In particular, it will probe the stability of the intermediates to determine how accurately the concentrations that were measured for these species reflect the levels that are produced in the body.