Identification of [(GS)₂AsSe]^- in rabbit bile by size-exclusion chromatography and simultaneous multielement-specific detection by inductively coupled plasma atomic emission spectroscopy

An arsenic-selenium metabolite that exhibited the same arsenic and selenium X-ray absorption nearedge spectra as the synthetic seleno-bis(S-glutathionyl) arsinium ion [(GS)₂AsSe]^- was recently detected in rabbit bile within 25 min after intravenous injection of rabbits with sodium selenite and sodium arsenite. X-ray absorption spectroscopy did not (and cannot) conclusively identify the sulfur-donor in the in vivo sample. After similar treatment of rabbits, we analyzed the collected bile samples by size-exclusion chromatography (SEC) using inductively coupled plasma atomic emission spectroscopy (ICP-AES) to monitor arsenic, selenium and sulfur simultaneously. The bulk of arsenic and selenium eluted in a single peak, the intensity of which was greatly increased upon spiking of the bile samples with synthethic [(GS)₂AsSe]^-. Hence, we identify [(GS)₂AsSe]^- as the major metabolite in bile after exposure of rabbits to selenite and arsenite. The reported SEC-ICP-AES method is the first chromatographic procedure to identify this biochemically important metabolite in biological fluids and is thus a true alternative to X-ray absorption spectroscopy, which is not available to many chemists.