Evaluation of a sequential extraction procedure for the speciation of heavy metals in sediments

The three-stage sequential extraction procedure for speciation of heavy metals, proposed by the Commission of the European Communities Bureau of Reference (BCR), has been applied to a freshwater sediment collected from the River Clyde, Lanarkshire, UK. Initial studies were carried out using flame atomic absorption spectrometry (FAAS). Iron, manganese and zinc could be determined in the sediment extracts by FAAS, but the technique proved insufficiently sensitive for the determination of chromium, copper, nickel and lead. Detection methods based on electrothermal AAS were therefore developed and applied. Furnace conditions were optimised for the determination of the four analytes mentioned, plus molybdenum and vanadium, in acetic acid, hydroxylammonium chloride and ammonium acetate matrices. Interferences by components in the sediment extracts necessitated analysis by the method of standard additions in most cases. The sequential extraction procedure was found to be both repeatable and reproducible. The amounts of analytes released by the sequential extraction procedure plus aqua regia digestion of the residue remaining after extraction were similar to those released by pseudo-total digestion of the sediment (using aqua regia).