Liquid chromatographic arsenic speciation with gas-phase chemiluminescence detection

We present a newly developed gas-phase chemiluminescence (CL) detection method for the separation and quantification of inorganic and organic arsenic species. Arsenite, arsenate, dimethylarsinic acid (DMA), and monomethylarsonic acid (MMA) were separated by anion exchange using carbonate-bicarbonate and NaOH eluents with step-gradient elution. The separated species were passed through a UV photooxidation reactor which decomposed the organic species and converted them to inorganic As(V). Subsequent on-line hydride generation with acid and sodium borohydride produces AsH3 and H2, which are separated from the liquid in a gas-liquid separator. The produced AsH3, driven by H2, reacts with ozone in a small reflective cell located atop a photomultiplier tube, resulting in intense CL. In the present form, the limits of detection (LODs, signal-to-noise = 3), based on peak height, for arsenite, arsenate, MMA, and DMA are 0.4, 0.2, 0.5, and 0.3 microg/L, respectively, for a 100 microL injected sample. This analyzer demonstrates the robustness of the CL detection system for arsenic and provides an affordable alternative to atomic spectrometry for use as a detector after chromatographic speciation. We found no significant practical interferences.