Determination of 8 Metal Elements in Soil by High-resolution Inductively Coupled Plasma-Mass Spectrometry with Microwave Digestion

Abstract

BACKGROUND Microwave digestion combined with inductively coupled plasma-mass spectrometry (ICP-MS) is a commonly used method for the determination of metal elements in soil samples. Different solvents can be used in the pretreatment, and the digestion method has a great influence on the accuracy of the analysis results. In addition, the accuracy of the results will be affected by the interference in the determination of some elements by ICP-MS. OBJECTIVES To accurately determine metal elements in soil samples by high resolution-inductively coupled plasma-mass spectrometry (HR-ICP-MS). METHODS Soil samples were digested by microwave using three different solvents, and 8 metal elements (Cr, Co, Ni, Cu, Zn, Pb, Cd and U) were determined by HR-ICP-MS. The digestion effects of the three acid digestion methods using different amounts of nitric acid, hydrochloric acid and hydrofluoric acid on certified soil reference materials were studied, and the optimal pretreatment procedure was determined. RESULTS The proposed procedures have been verified by national soil reference materials. It was found that the measured values of digestion method Ⅰ(6mL HNO3+3mL HCl+3mL HF) and digestion method Ⅱ(2mL HNO3+6mL HCl+1mL HF) were consistent with the certified values, using HR-ICP-MS without interference correction. The detection limits of both procedures were 0.001-0.715μg/g. The relative standard deviations (RSD, n=6) were all less than 7.0%. In terms of digestion, accuracy and precision, acid system Ⅰ was slightly better than acid system Ⅱ, but acid system Ⅱ had the least amount of acid. CONCLUSIONS The two preferred procedures have high applicability and reliability, and can be used for the direct determination of 8 metal elements in soil samples.

Keywords

• soil
• metal elements
• microwave digestion
• acid digestion
• high resolution-inductively coupled plasma-mass spectrometry