A Comparative Study of Metal Readsorption in the Application of a Three-Stage Sequential Extraction Scheme and Two Accelerated Versions (Ultrasonic and Single Extractions)

Accelerated methods for partitioning of Cd, Cr, Cu, Ni, Pb and Zn, such as the use of single and ultrasonic extractions are assessed in terms of readsorption and compared with the three-stage sequential extraction scheme (SES) of the Standards Measurements and Testing Programme (SM&T). The standard addition approach was employed for characterising the readsorption artefact by applying the above fractionation methods over different certified reference materials (CRMs), BCR 701, BCR 601 (lake sediments), and BCR 141R soil. Ultrasonic extractions provided higher readsorption, mainly for BCR 141R and 601 as compared to conventional SES, the role of ultrasound in the activation of adsorptive sites being significant. The single extraction approach seemed to be inadequate with samples containing large amounts of carbonates such as BCR 141 R but worked well with both lake sediments. The readsorption phenomena are mainly occurring in the most labile fraction (i.e. acid soluble) and has been observed to be matrix dependent. The extent of such phenomenon is also dependent on the extraction methodology, i.e conventional vs accelerated.