Graphite furnace atomic absorption spectrometry used for determination of total, EDTA and acetic acid extractable chromium and cobalt in soils.

Abstract

Methods for determination of both the total and extractable content of Cr and Co in soil samples were investigated. For the total content of metal, ultrasonic slurry sampling graphite furnace atomic absorption spectrometry was used and compared with conventional analyses after microwave digestion. The influence of grinding, leaching and homogeneity for slurry sampling was also examined. The concentration of the elements in the analyzed materials were in the range: 50 microg g(-1)-0.4% for Cr and 8-14 microg g(-1) for Co. Relative standard deviations (slurry sampling) were in the range 3%-12% for Cr and 0.3%-6% for Co determinations. The detection limit and characteristic mass (peak-area measurements) for Co were 0.14 microg g(-1) and 12.6 pg, respectively. For Cr less sensitive wavelengths were used. Excellent agreement with certified reference material was found for total Cr and Co using slurry sampling. EDTA and acetic acid extractions were performed, using protocols given by the Measurement and Testing Programme of the European Commission. The percentages extracted for the different soil samples were 0.3-1.0 for Cr and 2.5-24 for Co. To validate the accuracy of the extractable Cr, CRM 483 Sewage sludge amended soil was analyzed. The values found were 37% and 32% higher than the certified value for EDTA and acetic acid extractable Cr, respectively. The precision for extractable concentration of Cr and Co was about 6% or less. External calibration with aqueous standards, matched to contain the same reagents as the samples, was employed.