Extraction and Cleanup of Soil Arsenical Residues for Analysis by High Pressure Liquid Chromatographic–Graphite Furnace Atomic Absorption

Abstract

Abstract An analytical procedure for the extraction and cleanup of arsenical residues from soil was developed to meet the specific requirements for separation by high pressure liquid chromatography (HPLC) and on-line analysis by a graphite furnace atomic absorption spectrophotometer (GFAA). Soil samples were extracted with 2M aqueous NH4OH, cleaned on a carbon-Celite chromatographic column, concentrated to 1 g soil extract equivalent per mL, and determined by HPLC-GFAA. Recovery values were as follows: dimethylarsinic acid (cacodylic acid, CA) 90%; methanearsonic acid (MAA) 83%; arsenate 56%; and arsenite 64%. The limit of detection was 0.5 ppm in soil. Additional cleanup on cellulose thin layer chromatographic (TLC) plates improved sensitivity to less than 0.1 ppm and also served for confirmation of identity. The soil extract matrix did not appear to affect GFAA signal response. High salt content in concentrated soil samples altered the dimethylarsinic acid HPLC retention volume. By the time of analysis, arsenite was completely oxidized to arsenate in soil extractant.