Speciation of Arsenic and Selenium via Anion-Exchange HPLC with Sequential Plasma Emission Detection

Abstract

The speciation and quantification of arsenate, arsenite, selenate, and selenite was achieved through the use of anion-exchange HPLC with sequential inductively coupled plasma emission (ICP) detection. Earlier work has demonstrated the applicability of the ICP for multi-element HPLC detection of metal-containing moieties by using a polychromator system. Sequential detection for this purpose offers more flexibility than the fixed wavelength polychromator detector, yet is highly applicable to systems in which analyte signal is presented sequentially to the detector. Since the spectrometer for sequential ICP detection is considerably less complex than its polychromator counterpart, the instrumentation expense is considerably reduced. However, this approach is more demanding on the chromatography since it monitors only one channel at a time. Nevertheless, it is capable of extracting multi-element speciation information from a single run. Also, baseline resolution is not necessary with sequential detection if quantification is carried out using the peak height. Detection limits were 1.8 ng As/sec and 3.9 ng Se/sec. Absolute detection limits were 52 ng As(III), 140 ng Se(IV), 57 ng As(V), and 91 ng Se(VI). Reproducibility at the 2.8-μg level was found to be 4%, 7%, 6%, and 6%, respectively for As(III), Se(IV), As(V), and Se(VI), with a linear response through 9 μg for the lower oxidation states and 5 μg for the higher oxidation states.