Comparison of Digestion Methods for ICP-OES Analysis of a Wide Range of Analytes in Heavy Metal Contaminated Soil Samples with Specific Reference to Arsenic and Antimony

Abstract

Recommended alternative digestion methods for elemental analysis of soil often omit arsenic (As) and antimony (Sb) as viable analytes. In addition, comparisons of these methods for analysis of a wide range of elements by ICP-OES are few, limiting the viability of recommended methods. Four methods for the digestion of soils (microwave aqua regia, open aqua regia, microwave nitric, and open nitric) were assessed in seven field soil samples analysed by ICP-OES. Relative extraction strength and analytical precision were compared for 18 elements [aluminium (Al), iron (Fe), manganese (Mn), magnesium (Mg), calcium (Ca), potassium (K), phosphorus (P), sulfur (S), arsenic (As), cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), sodium (Na), nickel (Ni), lead (Pb), antimony (Sb), and zinc (Zn)] with the emphasis on obtaining optimal analytical results for the volatiles As and Sb. The microwave aqua regia digestion was found to give better elemental extraction and analytical variability for the widest range of analytes, with acceptable results for As and Sb. This method was found to give adequate recoveries for most analytes (excluding Ni, Cr, Co, and Na), and good precision in the analysis of standard material and further field samples (relative standard deviation <20%). The microwave aqua regia method used was determined to be a better multi-element (including As and Sb) alternative to the open aqua regia method than the current Australia and New Zealand (ANZECC) recommended alternative of microwave nitric digestion.