Arsenic and selenium speciation in coal fly ash extracts by ion chromatography-inductively coupled plasma mass spectrometry

Abstract

Ion chromatography (IC) coupled to inductively coupled plasma mass spectrometry (ICP-MS) affords a sensitive technique to quantify inorganic As and Se species at trace levels; however, few studies have used the multi-element capabilities of ICP-MS as a detector for chromatographic applications. Here, IC coupled with ICP-MS was used to determine As(iii), As(v), Se(iv), and Se(vi) in aqueous extracts of coal fly ash. All four species were resolved, with retention times of 1.1, 2.9, 4.8, and 6.3 min for As(iii), Se(iv), Se(vi), and As(v), respectively. Because all species were fully resolved, the resulting chromatograms were obtained by summing signal intensities form/z 75+m/z82. Absolute detection limits of 7.2, 87, 117, and 28 pg for As(iii), Se(iv), Se(vi), and As(v), respectively, were obtained, corresponding to 0.072, 0.868, 1.174, and 0.284 µg l–1 for a 100 µl injection volume. The technique was used to determine the speciation of As and Se in aqueous extracts of 24 coal fly ash samples including NIST SRM 1633b. The predominant species were As(v) and Se(iv), with As(iii) detected in two low pH fly ashes. Extraction of fly ashes at pH 5 altered the concentrations of total soluble As and Se but did not affect the predominant As and Se speciation.