Speciation of Arsenic Compounds in Drinking Water by Capillary Electrophoresis with Hydrodynamically Modified Electroosmotic Flow Detected Through Hydride Generation Inductively Coupled Plasma Mass Spectrometry With a Membrane Gas–Liquid Separator

Abstract

Capillary electrophoresis (CE) was used to speciate four environmentally significant, toxic forms of arsenic: arsenite, arsenate, monomethylarsonic acid and dimethylarsinic acid. Hydride generation (HG) was used to convert the species into their respective hydrides. The hydride species were detected with inductively coupled plasma mass spectrometry. The HG unit utilized a microporous PTFE tube as a gas–liquid separator. The injection mode for CE was electrokinetic in conjunction with the novel use of hydrodynamically modified electroosmotic flow (HMEOF). In HMEOF, the electroosmotic flow is modified by applying hydrodynamic pressure opposite to the direction of the electroosmotic flow. HMEOF provides the capability of injecting increased quantities of analyte by offsetting the electroosmotic flow, which limits conventional electrokinetic injection. In order to correct for imprecisions in the electrokinetic injection in matrices of different ionic strength, the use of a surrogate for the injection of arsenic species was investigated. Germanium was investigated because it forms a hydride and has a low natural occurrence. The separation also utilized HMEOF, which allowed for greater freedom in buffer choice. The detection limits in distilled, de-ionized water were 25, 6, 9 and 58 ppt for the four species listed above, respectively. The detection limit was calculated from 3.14 σ _n-1 of seven replicate injections and represents the precision of measuring the ratio of the area of the arsenic peaks to the area of a germanium surrogate peak. Standard addition was used to determine arsenate in drinking water samples. Recoveries of arsenite and arsenate from drinking water samples are reported using germanium as a surrogate to correct for sampling bias of the electrokinetic injection.