Spectrophotometric determination of phosphate/arsenate in aqueous solution by a modified molybdenum blue method and reduction of arsenate by dithionite

ANYL 269

Gregory Poskrebyshev, poskr@yahoo.com1, Susanna Tsang, susannatsang1981@yahoo.com1, Frank Phu, frankphu@gmail.com2, and Marc M. Baum, m.baum@oak-crest.org2. (1) Department of Chemistry, Oak-Crest Institute of Science, 2275 E.Foothill blvd, Pasadena, CA 91107, (2) Department of Chemistry, Oak Crest Institute of Science, 2275 E. Foothill Blvd., Pasadena, CA 91107
A modified molybdenum blue method for fast and accurate measurement of arsenate and phosphate in aqueous solution at concentrations below 10 ìmol/L is reported. The modification consists of optimizing the composition of the molybdenum-containing solution (potassium antimony tartrate, ammonium molybdate, sulfuric acid). Selective reduction of arsenate by sodium dithionite is used to determine phosphate concentrations, and for the speciation of arsenate and arsenite, in an aqueous mixture according to the scheme developed by Johnston and Pilson. Sodium dithionite is used for the first time to achieve complete, fast (< 10 minutes), and selective reduction of arsenate in neutral solution. These two significant improvements afforded a colorimetric limit for As detection near 1 ppb, which easily meets the requirements imposed by the revised EPA threshold levels for As in drinking water.
 

Analytical Approaches, Spectroscopy
8:30 AM-12:00 PM, Wednesday, 13 September 2006 Moscone Center -- Room 124, Oral

Division of Analytical Chemistry

The 232nd ACS National Meeting, San Francisco, CA, September 10-14, 2006