A rapid plant digestion method for analysis of ρ and certain cations by inductively coupled plasma emission spectrometry

Abstract

Quick and reliable tissue testing is important in a soil fertility program to ensure adequate yields for profitability. However, commonly used tissue tests for elements require from 2 to 6 hours for digestion and extraction of samples. A rapid digestion procedure for P and certain cations that require only an analytical balance and volumetric glassware was therefore developed to assay plant tissues by inductively-coupled plasma emission spectroscopy. The method is based on the oxidation and solubilization of plant organic matter created by the heat of solution when 30% hydrogen peroxide (H2O2) is added to concentrated sulfuric acid (H2SO4). This step requires about 30 minutes for 40 samples. No further wet-digestion is required for sample preparation because the high temperature of the plasma converts all complexes and organics in the digest to elemental forms. For the determination of P by the colorimetric molybdate-blue method, an additional heating is required to eliminate unreacted peroxide. Results of the proposed procedure compared well with certified values from the National Bureau of Standards plant materials and with results from a nitric acid and a Kjeldahl digestion procedures. Elemental concentrations found with the proposed method also compared well with the two conventional methods for different plant species and plant parts. While recoveries with the proposed procedures for P, K, Ca, Mg, Zn, Cu, and Mn appeared to be within the sensitivities needed for nutritional diagnostic purposes, recoveries of Fe and Al were low. The ease and rapidity of the procedure could make it useful for routine analysis, or for early-season tissue analysis where correction of P and certain cation deficiencies could result in increased profits. The method should be especially useful for screening small numbers of samples.