Simultaneous Determination of V, Cr, Ni, Ge and As in Geochemical Samples by ICP-MS Combined with Microwave Digestion Sample Preparation

A microwave digestion method to simultaneously determine V, Cr, Ni, Ge and As in geochemical samples by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) is proposed. There are two main factors to influence the method accuracy: Cr and Ni released from stainless bomb could contaminate the samples by high press digestion and volatile elements, such as Ge and As, lost during pretreatment, and polyatomic molecular ions have mass influence on the determination by ICP-MS. In order to eliminate these two kinds of influences, four kinds of digestion methods were compared, including microwave digestion with nitric acid/aqua regia extraction and high pressure digestion with nitric acid/aqua regia extraction. The method by microwave digestion instead of high pressure digestion avoids the problem of contamination of Cr and Ni and loss of Ge and As with short digestion times. The nitric acid extraction, avoiding the addition of Cl^-, has better analysis effect when compared with aqua regia extraction. A helium dilution technique based on the octopole reaction system ICP-MS was applied to decrease the interference of polyatomic molecular ions, such as ³⁷Cl¹⁴N interference on ⁵¹V, ³⁵Cl¹⁶OH interference on ⁵²Cr, ³⁵Cl³⁷Cl interference on ⁷²Ge and ⁴⁰Ar³⁵Cl interference on ⁷⁵As. Based on the study of rock, stream sediments and soil national standard material by ICP-MS combined with nitric acid extraction, the results showed that the detection limits of V, Cr, Ni, Ge, and As by the proposed method were 1.09 μg/g, 0.19 μg/g, 0.55 μg/g, 0.02 μg/g and 0.50 μg/g, respectively. The RSDs were less than 4%. The detection limits of V, Cr and Ni by high pressure digestion were 3.48 μg/g, 13.09 μg/g and 21.67 μg/g, respectively. The proposed method was simple, time-saving (from 48 h to 2 h) and has the capability of simultaneous determination of multielements with low detection limits.