Classical dry ashing of biological and agricultural materials. Part II. Losses of analytes due to their retention in an insoluble residue

Abstract

Retention of selected analytes (Cd , Cr, Cu, Mn, Pb, Zn) in solid residue which remains undissolved in 1.5% HNO 3 used as a leaching medium after classical dry ashing of ten materials (alfalfa lea ves, NIST SRM 1569 Brewer' s Yeast, blood meal, meat-bone meal, feather-bone meal, silage residue , litter, pond sediment, coal waste , IRM NSC-21 Industrial Compost Vitahum) was studied . The elements remaining in the residue were determined mainly b y AAS after dissolution of this residue in the mix - ture of HF + HNO 3. In several instances, pressurized wet digestion, alkaline fusion, stripping voltammetry and instrumental neu- tron acti vation were also applied. Increasing concentr ation of mineral acid in leaching medium which does not contain HF, plus increasing final volume of the solution, suppresses significantly this type of analyte losses in the majority of matrices tested . However, for industrial compost and standard reference material NIST 1569 Br ewer' s Yeast, application of an HF step is neces - sary for quantitative release of the analytes (in particular chromium) into solution.