Microwave digestion for analysis of metals in soil

Abstract

Microwave digestion using either only nitric acid or a mixture of nitric acid and hydrogen peroxide is an innovative technique used widely for elemental analysis of soil and plant samples. Only limited information, however, is available on comparisons of digestions with or without hydrogen peroxide. The objective of this study was to investigate the effect of the use of hydrogen peroxide on the analytical results for several metals in soil samples. Three mineral and four organic soil samples were used in this study. The soils were slightly acidic, and the organic carbon ranged from 0.38 to 1.26% for the mineral soils and from 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), chromium (Cr), and manganese (Mn) using inductively coupled plasma spectroscopy. In general, the analytical results obtained with nitric acid alone were not significantly different from those with the nitric acid and hydrogen peroxide mixture regardless of organic carbon content. Since hydrogen peroxide did not promote additional dissolution of these metals in this study, nitric acid alone in microwave digestion is sufficient for determining metal composition of soils.