Determination of cadmium and molybdenum in soil extracts by graphite furnace atomic-absorption and inductively coupled plasma spectrometry

Abstract

Methods for the direct determination of Cd and Mo in soil extracts by graphite furnace atomic-absorption spectrometry (GFAAS) and inductively coupled plasma (ICP) spectrometry were developed and optimum operating conditions, analyte modifiers and matrix interferences were investigated. The use of a mini-furnace allowing an atomisation temperature of 1200 °C and the addition of Mo + H₂O₂+ HNO₃ as a matrix modifier are the most important features for the successful direct determination of Cd by GFAAS. The characteristic amounts are 0.164 pg for Cd and 8.39 pg for Mo by GFAAS, with relative standard deviations (RSD) of 7.5% and 4%, respectively, based on ten replicate measurements on a soil extract. The ICP detection limits are 1.49 µg l^–1 for Cd and 4.09 µg l^–1 for Mo, with RSDs better than 1%. Matrix interferences in ICP are negligible compared with GFAAS and the precision of the former technique is better, but the sensitivity of GFAAS is clearly superior. The results for Cd and Mo determinations in some soil extracts by the two proposed methods agreed closely.