Evaluation of the acetate buffer attack of a sequential extraction scheme for marine particulate metal speciation studies by scanning electron microscopy with energy dispersive X-ray analysis

Scanning electron microscopy, with energy dispersive X-ray analysis (SEM-EDX), has been used to evaluate and possibly optimize, the first step (acetate buffer attack for exchangeable and carbonatic fractions) of a sequential selective extraction scheme. The extraction has been performed on two different particulates, a certified reference plankton and a real marine suspended particulate, using an increased acetate concentration and various solid/extractant ratios. SEM-EDX has been performed on the non treated particulates and on the residues after the attack, and the results related to the spectroscopic analyses of the extracts, allowed us to verify that even if efficiency has been optimized, the procedure still suffers of a lack of selectivity. Nevertheless, SEM data were helpful to put forward some interesting speciation hypothesis, that would have been certainly different, and probably wrong, if based on analyses of the extracts only. (C) 1998 Elsevier Science B.V.