EVALUATION OF THE USE OF H2SO4-H2O2 DIGESTIONS FOR THE ELEMENTAL ANALYSIS OF PLANT-TISSUE BY ICP SPECTROMETRY

Various H2SO4-H2O2 digestion procedures have been described as suitable for the determination of the concentrations of N and other elements in plant tissue with a single digest. Given relatively low sulfate concentrations in the final digest, the procedure described by Parkinson and Allen was chosen as one of the most promising of the H2SO4-H2O2 digestions for ICP analysis. This procedure was evaluated by using it, as well as standard digestion procedures, to digest NIST standard reference material prior to ICP analysis. The ICP-determined concentrations of the H2SO4-H2O2 digests were generally found to correspond closely with NIST certified concentrations across all analyzed elements. However, Ca concentrations were underestimated for a standard reference sample having a certified concentration of 31500-mu-g/g, indicative of CaSO4 precipitation at higher Ca sample concentrations. Moreover, subsequent analysis of tropical grass samples was hampered by considerable ICP drift for all elements analyzed, suggesting that the reproducibility of ICP readings of digests with high sulfuric acid concentrations is greatly affected by the sample matrix.