Mercuric chloride toxicity in mammals can be overcome by co-administration of sodium selenite. We report a study of the mutual detoxification product in rabbit plasma, and of a Hg-Se-S-containing species synthesized by addition of equimolar mercuric chloride and sodium selenite to aqueous, buffered glutathione. Chromatographic purification of this Hg-Se-S species and subsequent structural analysis by Se and Hg extended X-ray absorption fine structure (EXAFS) spectroscopy revealed the presence of four-coordinate Se and Hg entities separated by 2.61 A. Hg and Se near-edge X-ray absorption spectroscopy of erythrocytes, plasma, and bile of rabbits that had been injected with solutions of sodium selenite and mercuric chloride showed that Hg and Se in plasma samples exhibited X-ray absorption spectra that were essentially identical to those of the synthetic Hg-Se-S species. Thus, the molecular detoxification product of sodium selenite and mercuric chloride in rabbits exhibits similarities to the synthetic Hg-Se-S species. The underlying molecular mechanism for the formation of the Hg-Se-S species is discussed.

A simple diagnostic test for the detection of bovine spongiform encephalopathy (BSE), based on a commercially available time-resolved fluorescence immunoassay (DELFIA) for the measurement of the normal and disease-associated isoforms of prion protein (PrP), is described. The isoforms are sequentially extracted from homogenized bovine brain tissue using two concentrations of guanidine hydrochloride. This procedure initially extracts a soluble isoform and subsequently a less soluble disease-associated aggregated isoform. Following quantification of the two fractions, the percentage of the insoluble prion becomes a measurable parameter, independent of protein concentration, clearly identifying normal from infected animals displaying clinical signs of BSE. The mean percentages of insoluble PrP in brain tissue from 60 BSE-confirmed-positive cattle and 100 cattle that had never been exposed to the disease were 52.6% (SD = 22.8) and 3.9% (SD = 1.5), respectively. The assay is sensitive, with a detection limit of less than 50 pg PrP, and is robust and precise (CVs < 10%) over the appropriate working range.

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) 2 AsSe]À 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 sulfurdonor 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) 2 AsSe] À . Hence, we identify [(GS) 2 AsSe] À 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.

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In order to confirm the solution structure of [(GS) 2 AsSe] À (GS = glutathione), we have investigated the retention behaviour of a [(GS) 2 AsSe] À /oxidized glutathione (GSSG) mixture on a Sephadex G-25 (SF) column with Tris buffers (0.1 mol dm À3 , pH 8.0) containing various surfactants at concentrations above the critical micellar concentration (CMC): hexadecyltrimethlammonium bromide (HDTAB; 30, 40 and 50 mmol dm À3 ); dodecyltrimethylammonium bromide (DDTAB; 50 mmol dm À3 ); and sodium lauryl sulfate (SLS; 50 mmol dm À3 ). An inductively coupled plasma atomic emission spectrometer (ICP AES) provided simultaneous on-line detection of arsenic, selenium and sulfur in the column effluent. The chromatographic retention behaviour was used to investigate the association of both compounds with the positively charged micelles (HDTAB and DDTAB mobile phases). The relative strength of association with the micelles provided insight into the effective negative charge on [(GS) 2 AsSe] À and GSSG. The chromatograms obtained with 50 mmol dm À3 HDTAB indicated that two glutathione molecules are associated with the elution of an arsenic-selenium compound. Combined, these chromatographic data strongly support the spectroscopically derived solution structure of [(GS) 2 AsSe] À .

In order to separate the potential arsenite metabolites methylarsonous acid and dimethylarsinous acid from arsenite, arsenate, methylarsonic acid and dimethylarsinic acid, the pH‐dependent retention behaviour of all six arsenic compounds was studied on a Hamilton PRP‐X100 anion‐exchange column with 30 mM phosphate buffers (pH 5, 6, 7, 8 and 9) containing 20% (v/v) methanol as mobile phase and employing an inductively coupled plasma atomic emission spectrometer (ICP–AES) as the arsenic‐specific detector. Baseline separation of dimethylarsinic acid, methylarsonous acid, methylarsonic acid, arsenate and dimethylarsinous acid was achieved with a 30 mmol dm−3 phosphate buffer (pH 5)–methanol mixture (80:20, v/v) in 25 min. Arsenite is not baseline‐separated from dimethylarsinic acid under these conditions. Copyright © 1999 John Wiley & Sons, Ltd.

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Experiments were carried out to explore the effect of an electric field upon atomic species introduced into a flame. The study involves components from a conventional flame atomic absorption apparatus with 10 × 10-cm parallel plate electrodes as the cathode and the 5-cm slot burner head as the anode. A marked decrease in the emission and absorption of many atomic species was observed, and quantification of the effect was carried out. The effect has been interpreted as a disturbance of the equilibrium, Me ≈ Me+ + e−. Relative decreases in absorption and emission were found to be functions of applied voltage and analyte concentration at low voltages, and constant for high voltages (≍ −2000 V). Temporal behavior of the effect has been investigated by observation of the speed of restoration of the emission signal from Na (589.16 nm), Sr (460.86 nm), and Sr+ (407.89 nm) after rapid elimination of the electric field. The effects were also studied as a function of viewing position in the flame for optimization of the position and comparison of the temporal behavior with the speed of the flame gases.