Sodium 2,3-dimercapto-1-propane sulfonate (
DMPS) has been used to treat acute
arsenic poisoning. Presumably
DMPS functions by chelating some
arsenic species to increase the excretion of
arsenic from the body. However, the excreted complex of
DMPS with
arsenic has not been detected. Here we describe a
DMPS complex with
monomethylarsonous acid (
MMA(III)), a key trivalent
arsenic in the
arsenic methylation process, and show the presence of the
DMPS-
MMA(III) complex in human urine after the administration of
DMPS. The
DMPS-
MMA(III) complex was characterized using electrospray tandem mass spectrometry and determined by using HPLC separation with hydride generation atomic fluorescence detection (HGAFD). The
DMPS-
MMA(III) complex did not form a volatile hydride with
borohydride treatment. On-line digestion with 0.1 M
sodium hydroxide following HPLC separation decomposed the
DMPS-
MMA(III) complex and allowed for the subsequent quantification by hydride generation atomic fluorescence.
Arsenite (As(III)),
arsenate (As(V)),
monomethylarsonic acid (MMA(V)),
dimethylarsinic acid (DMA(V)),
MMA(III), and
DMPS-
MMA(III) complex were analyzed in urine samples from human subjects collected after the ingestion of 300 mg of
DMPS. The administration of
DMPS resulted in a decrease of the DMA(V) concentration and an increase of the MMA(V) concentration excreted in the urine, confirming the previous results. The finding of the
DMPS-
MMA(III) complex in human urine after
DMPS treatment provides an explanation for the inhibition of
arsenic methylation by
DMPS. Because
MMA(III) is the substrate for the biomethylation of
arsenic from MMA(V) to DMA(V), the formation of
DMPS-
MMA(III) complex would reduce the availability of
MMA(III) for the subsequent biomethylation.