Development of a Method for the Microwave-assisted Digestion of Soils Using Dilute Acids and the Simultaneous Determination of 18 Trace Elements by Inductively Coupled Plasma Mass Spectrometry

摘要

A simple two-step microwave-assisted digestion process employing dilute acids was developed for the simultaneous determination of 18 elements (Li, Be, V, Cr, Co, Ni, Cu, Zn, Ga, As, Sr, Mo, Sn, Ba, Tl, Pb, Bi, and U) in soil by inductively coupled plasma mass spectrometry. The soil sample (similar to 0.3 g) was initially digested using a mixture of 10% (v/v) HNO3 + 7% (v/v) HF. Subsequently, the HF was removed by evaporation, and the final solution made into a dilute HNO3 + HCl mixture to prevent the elements from hydrolyzing. The goal was to develop a digestion method for monitoring the heavy metal content in soil samples, especially with a view to reduce the acid content and to enable the sample digests to be analyzed by inductively coupled plasma techniques. The proposed method was validated by digesting and analyzing a certified soil reference material GBW-07409. The percentage recovery of the above trace elements varied from 86107%. Detection limits ranging from 0.001 to 0.04 mg kg(-1) and relative standard deviation values lower than 10% were obtained. A standard digestion (total) procedure for soil analysis based on the USEPA 3052 method was applied and the results compared with those obtained by the developed method. Later, a sample of soil collected from Tummalapalle, Andhra Pradesh, India, where recently large uranium deposits have been identified and mining commenced, was analyzed, and the results are presented.