Coupled chromatography-atomic spectrometry for arsenic speciation—a comparative study

Abstract

Several methods for the quantitative determination of different forms of arsenic (As^III, As^V, monomethyl and dimethyl) in a variety of samples are described and compared. In each instance separation is achieved by chromatographic means, using either gas (GC) or high-performance liquid chromatography (HPLC), with detection by atomic spectrometry, namely flame atomic absorption spectrometry (FAAS), flame atomic fluorescence spectrometry (FAFS) and inductively coupled plasma atomic emission spectrometry (ICP-AES). For the GC separation it is necessary to derivatise the As compounds either as the hydrides or as the methylthioglycolates. As the arsenic hydrides can be pre-concentrated using cryogenic trapping, this yields the lowest detection limits. The As species studied can be separated without derivatisation by HPLC but after HPLC separation hydride generation can be used to increase the sensitivity for FAAS, FAFS and ICP-AES. While each technique is best suited to certain applications, the hydride generation-cryogenic trapping-GC-FAAS system is capable of detection at the sub-p.p.b. level (0.22–0.55 ng absolute for different species) and is preferred for low-level As samples. When levels permit, HPLC-hydride generation-FAAS is probably the simplest routine method and HPLC-hydride generation-ICP-AES will probably be preferred for multi-element analysis.