MICROWAVE DIGESTION FOR ANALYSIS OF METALS IN SOIL

Microwave digestion using either only nitric acid or a mixture of nitr ic acid and hydrogen peroxide is an innovative technique used widely f or elemental analysis of soil and plant samples. Only limited informat ion, however, is available on comparisons of digestions with or withou t hydrogen peroxide. The objective of this study was to investigate th e effect of the use of hydrogen peroxide on the analytical results for several metals in soil samples. Three mineral and four organic soil s amples were used in this study. The soils were slightly acidic, and th e organic carbon ranged from 0.38 to 1.26% for the mineral soils and f rom 17 to 38% for the organic samples. After microwave digestion, the soil samples were analyzed for aluminum (Al), iron (Fe), magnesium (Mg ), zinc (Zn), copper (Cu), lead (Pb), cadmium (Cd), nickel (Ni), chrom ium (Cr), and manganese (Mn) using inductively coupled plasma spectros copy. In general, the analytical results obtained with nitric acid alo ne were not significantly different from those with the nitric acid an d hydrogen peroxide mixture regardless of organic carbon content. Sinc e hydrogen peroxide did not promote additional dissolution of these me tals in this study, nitric acid alone in microwave digestion is suffic ient for determining metal composition of soils.