Identification and determination of arsenic and phosphorus species in environmental and biological samples

Abstract

The surface of indium phosphide single crystals exposed to synthetic lung fluid (Gamble solution) has been investigated. An oxygen depth profile, obtained by employing the 3.035 MeV resonance in the elastic scattering of alpha particles from 16O, detected oxygen at maximum concentrations of 24% in a layer approximately 1000 A thick. O:In and O:P ratios were found to increase with prolonged exposure time as determined by XPS, although binding energies and peak fwhm's remained relatively constant. The surface concentration of indium was found to be decreased in this 1000 A layer. Indium was detected in the Gamble solution, confirming that indium was leached from the InP surface. The similarity of P:In ratios at all lengths of exposure suggests that phosphorus was also leached by the Gamble solution. An efficient method for determining arsenic species As III, As V, methylarsonic acid and dimethylarsinic acid in groundwater samples has been developed. Ion exchange chromatography using a tandem SCX/SAX column was used to separate the four species which were analyzed using hydride generation atomic absorption spectroscopy (IEX/HGAAS). The method produced excellent separation, and off-column arsenic fraction total concentrations were generally within 10% of measured total arsenic concentrations. IEX/HGAAS was used to speciate arsenic in groundwater samples collected from a suspected arsenic contamination site at an industrial facility in Missouri. Results of the speciation analysis provided evidence to substantiate the presence of high naturally-occurring arsenic in groundwater at the site. Trivalent arsenic was the predominant species detected. The occurrence of trivalent arsenic was consistent with the reducing conditions of the alluvial aquifer and the high iron oxide concentrations detected in soil at the site. Though sensitive, the traditional IEX/HGAAS method for speciating arsenic is tedious and time-consuming. Analysis of a single sample can require as much as eight hours. A microscale SPE/PIXE analysis method was investigated. This method allows for preconcentration of arsenic species by extraction onto an SPE column containing ion exchange resin. Because PIXE is not species-sensitive, the arsenic-containing resin was analyzed directly, thereby eliminating digestion and reduction requirements imposed by the HGAAS method. Preliminary results gave excellent retention for As V and DMA over the concentration range analyzed. As III and MMA were not significantly retained on the SAX resin under any of the extraction conditions tested.