Determination of rare earth elements, uranium and thorium in soil samples by microwave-assisted acid digestion and inductively coupled plasma mass spectrometry.

This paper presents a simple microwave digestion method for soil samples leading to correct determination of the rare earth elements (Ce, La, Nd, Sc), uranium (U) and thorium (Th) using inductively coupled plasma mass spectrometry (ICP-MS). Six soil samples were collected from different depths (0-0.1, 0.1-0.3, 0.3-1.0, 1.0-2.0, 2.0-3.0 and 5.0-8.0 m) in Phuket province, Thailand. The samples were decomposed using microwave-assisted acid digestion at four different acid conditions including (I) 20 mL concentrated nitric acid; (II) 20 mL concentrated hydrochloric acid; (III) mixture of 8 mL nitric acid and 12 mL hydrochloric acid; and (IV) mixture of 12 mL nitric acid and 8 mL hydrochloric acid. Instrumental neutron activation analysis (INAA) was also applied for determination of REEs, U and Th in those soil samples to compare the results. It was found that the concentrations of Ce, La, Nd, Sc, U and Th in all soil samples obtained by ICP-MS using concentrated nitric acid had acceptable agreement with INAA results. The measured concentrations of Ce, La, Nd, Sc, U and Th in the soil samples ranged within 260-461, 153-922, 87-632, 10-16, 33-134 and 156-323 mg/kg, respectively. [ABSTRACT FROM AUTHOR]