Digestion procedures for the determination of antimony and arsenic in small amounts of peat samples by hydride generation-atomic absorption spectrometry

Closed-pressurised and open vessel digestion procedures for the mineralisat ion of small amounts (similar to 100mg) of peat samples have been developed and evaluated. The two trace elements As and Sb were quantified in the dil uted digests by flow injection-hydride generation-atomic absorption spectro metry (FI-HC-AAS). Optimisation of the analytical procedures was carried ou t with two bulk peat materials one of which was prepared as internal refere nce material. Both peat specimens were additionally characterised by instru mental neutron activation analysis with respect to their concentrations of As and Sb. Good agreement between instrumental neutron activation analysis (INAA) results and concentrations determined by HG-AAS were obtained. The u se of adequate reference materials during the course of all experiments gua ranteed precise and accurate results. Various acid mixtures with and withou t hydrofluoric acid were tested, because preliminary experiments revealed t hat HF in the digestion mixture leads to the formation of the gaseous AsF5 resulting in diminished recoveries of As when open vessel digestion procedu res are employed. Avoiding HF for mineralisation of peat led to low recover ies for Sb because distinct amounts of Sb are associated with silicates. Cl osed-pressurised vessel digestion proved to be less effective compared to o pen vessel mineralisation. For successful quantification of both elements, two digestion procedures are needed, one without HF for As and another one with HF to liberate Sb from the silicates. The optimised open vessel digest ion procedure was applied to the determination of ancient peat samples dati ng back to 9300 calendar years before present. Concentrations of both eleme nts showed a broad spread with values ranging from 18 to 1500 and 300 to 57 00 ng g(-1) for Sb and As, respectively. (C) 2001 Elsevier Science B.V. All rights reserved.