AN INTERLABORATORY COMPARISON OF A STANDARDIZED EDTA EXTRACTION PROCEDURE FOR THE ANALYSIS OF AVAILABLE TRACE-ELEMENTS IN 2 QUALITY-CONTROLSOILS

A standardised EDTA extraction procedure was tested collaboratively by six laboratories using two in-house reference soils identified as soi l A and soil B. The extracts were analysed for Zn. Cu, Pb and Mn by In ductively Coupled Plasma Spectrometry. Concentrations of extractable e lements in soil A were generally much lower than those found in soil B . All laboratories produced some extreme outlying results, most of the se were produced in soil B. Results for Mn were the most variable, wit h a range of 63.4-100.3 mug g-1 in soil A and 226.4-415.3 mug g-1 in s oil B. In both soils, one laboratory reported high values for Zn and M n and, one laboratory, for soil B, produced values for all four elemen ts which were consistently low. If outlying results are ignored, the r esults from most laboratories were in reasonable agreement for all ele ments except Mn.