Precise Nd isotope analysis of igneous rocks using cation exchange chromatography and thermal ionization mass spectrometry (TIMS)

Abstract

We report a procedure that separates Nd from silicate rock samples using cation exchange chromatography allowing 143Nd/144Nd ratio analyses to be performed by thermal ionization mass spectrometry (TIMS). The procedure obtains the Nd fraction using a two-step column separation. First, a rare earth element (REE) fraction is separated via a cation exchange column with HCl as the eluent. Then, Nd is separated from this REE fraction using a second cation exchange column with α-hydroxy isobutric acid (HIBA) as the eluent. The procedural Nd blanks measured for each step are very low and negligible for 143Nd/144Nd ratios in natural rock samples. The Nd yields are high, with more than 90 % of Nd recovered during each step. Repeated analysis of 143Nd/144Nd ratios in the JNdi-1 standard solution gave a mean value of 0.512096 ± 0.000014 (2 SD, n = 144, RSD % = 0.0014), which is in good agreement with those reported in previous studies. The 143Nd/144Nd ratio obtained for the corrected JNdi-1 fractions using the technique in our laboratory was 0.512094 ± 0.000011 (2 SD, n = 4). We also measured 143Nd/144Nd ratios in several geochemical igneous rock reference materials (JB-la, JB-2, JA-1, and JR-1) producing mean values consistent with available data. These results indicate that the technique for Nd isotope analysis employed at our laboratory provides reliable and accurate data for geochemical studies.