title: Quantitative trace-level speciation of arsenite and arsenate in drinking water by ion chromatography.
abstract: We describe an improved method for the determination of inorganic arsenic in drinking water. The method is based on comprehensive optimization of the anion-exchange ion chromatographic (IC) separation of arsenite and arsenate with post-column generation and detection of the arsenate-molybdate heteropoly acid (AMHPA) complex ion. The arsenite capacity factor was improved from 0.081 to 0.13 by using a mobile phase (2.0 mL min(-1)) composed of 2.5 mM Na2CO3 and 0.91 mM NaHCO3 (pH 10.5). A post-column photo-oxidation reactor (2.5 m x 0.7 mm) was optimized (0.37 microM potassium persulfate at 0.50 mL min(-1)) such that arsenite was converted to arsenate with 99.8 +/- 4.2% efficiency. Multi-variate optimization of the complexation reaction conditions yielded the following levels: 1.3 mM ammonium molybdate, 7.7 mM ascorbic acid, 0.48 M nitric acid, 0.17 mM potassium antimony tartrate, and 1.0% (v/v) glycerol. A long-path length flow cell (Teflon AF, 100-cm) was used to measure the absorption of the AMHPA complex (818 +/- 2 nm). Figures of merit for arsenite/arsenate include: limit of detection (1.6/0.40 microg L(-1)): standard error in absorbance (5.1 x 10(-3)/3.5 x 10(-3)); and sensitivity (2.9 x 10(-3)/2.2 x 10(-3) absorbance units per ppb). Successful application of the method to fortified surface and ground waters (100 microL samples) is also described.
authors.affiliation: Department of Chemistry, University of Wisconsin-Milwaukee, 53211, USA.
authors.forename: Rebecca L
authors.initials: RL
authors.lastname: Johnson
authors.forename: Joseph H
authors.initials: JH
authors.lastname: Aldstad
mesh_terms: D001149:Arsenates / Q000032:analysis*; D018053:Arsenites / Q000032:analysis*; D002852:Chromatography, Ion Exchange / Q000379:methods; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D001149:Arsenates; D018053:Arsenites; D014874:Water Pollutants, Chemical; C015001:arsenite; C025657:arsenic acid