Comparison of two sequential extraction procedures for metal fractionation in sediment samples

Two sequential extraction procedures (a 3-step protocol proposed by the Standards, Measurements and Testing programme (SM&T – formerly BCR) of the European Union and a modified Förtsner 5-step procedure) have been compared. The comparison has been carried out by analyzing a Certified Reference Material (CRM 601 – Lake sediment) and five different sediment samples collected in the Orbetello Lagoon (Central Italy). Prior to the comparison, the analytical performances of the laboratory have been evaluated on the CRM 601; this CRM has been recently certified for the content of Cd, Cr, Cu, Ni, Pb and Zn in the three fractions resulting by applying the SM&T 3-step procedure. Results of this evaluation showed the high reliability of the analytical performances of the laboratory for all considered metals. Results of the comparison between 3- and 5-step procedures showed no differences for Zn and Cd whereas significant differences have been found for Pb, above all, and for Cr, Ni and Cu relatively to the oxidisable fraction.