Extraction of geological materials with mineral acids for the determination of arsenic, antimony, bismuth and selenium by hydride generation atomic absorption spectrometry

Abstract

Data are presented for the hydride generation atomic absorption spectrometric determination of arsenic, antimony, bismuth and selenium in stream sediments and a certified reference material (CPB-1 Lead Concentrate) using six different extraction media, viz., hydrochloric acid; nitric acid; 7 M nitric acid; nitric acidsulphuric acid (9 + 1); aqua regia; and reversed aqua regia (HNO₃+ HCl, 3 + 1). Extraction with 7 M nitric acid was performed in test-tubes placed in a drilled out heating block (110 °C, 3.5 h). All other extractions were carried out overnight in 50-ml calibrated flasks placed in a water-bath. Bismuth was extracted quantitatively by all the extraction media. Arsenic and selenium were extracted completely by each of the media used, except for hydrochloric acid. Antimony was extracted completely by only two of the media, viz., aqua regia and reversed aqua regia. Selenium is converted to the +4 oxidation state on extraction with aqua regia and reversed aqua regia, i.e., selenium(VI) is reduced to selenium(IV), and the lower oxidation states are oxidised to selenium(IV). Hence the extracts can be analysed for selenium without pre-reduction to selenium(IV), which is necessary for hydride generation atomic absorption spectrometry. The nitric acid-hydrochloric acid mixtures used bring arsenic, antimony, bismuth and selenium quantitatively into solution and are, therefore, suitable for the sequential or simultaneous determination of these elements in a single sample solution. The speciation of selenium in stream sediments and surface waters is discussed.