High-precision lithium isotopic analysis using the Nu Sapphire MC-ICP-MS

Here, we present a high-precision analytical method for lithium (Li) isotopic analysis using standard-sample bracketing on a Nu Sapphire collision cell multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS). A modified chemical purification procedure and optimized instrumental setup allow high-precision determination of Li isotopic ratios. A precision of +/- 0.13 to 0.23 parts per thousand (2SD) has been achieved based on repeat measurements of Li standard IRMM-016 and geological reference materials, BCR-2 and JG-2, over an eight-month period. We also evaluate factors that may lead to instrumental mass fractionations, e.g., Li concentration mismatch between the sample and standard, and the potential effect of the Na matrix. The obtained delta Li-7 values of eight international reference materials (IRMM-016, BHVO-2, BCR-2, RGM-1, AGV-2, G-2, GSP-2, and JG-2) are consistent with published data within uncertainty (+/- 2SD). In addition, we report seventeen Chinese geological reference materials from NRCG with the lowest Li content at about 2 mu g g(-1). Among them, the Li isotopic compositions of GSR-1, GSR-6, and GSR-12 are in agreement with values published in the literature, and delta Li-7 values of the other fourteen NRCG samples are reported for the first time, including andesite GSR-2: 8.27 +/- 0.14 parts per thousand, basalt GSR-3: 5.72 +/- 0.18 parts per thousand, sandstone GSR-4: -3.19 +/- 0.31 parts per thousand, syenite GSR-7: 1.91 +/- 0.24 parts per thousand, trachyte GSR-8: 4.77 +/- 0.21 parts per thousand, diorite GSR-9: 3.47 +/- 0.21 parts per thousand, gabbro GSR-10: 6.36 +/- 0.35 parts per thousand, rhyolite GSR-11: 2.50 +/- 0.15 parts per thousand, calcite GSR-13: 7.17 +/- 0.38 parts per thousand, granite gneiss GSR-14: 4.49 +/- 0.15 parts per thousand, hornblendite GSR-15: 3.45 +/- 0.19 parts per thousand, diabase GSR-16: 3.28 +/- 0.24 parts per thousand, kimberlite GSR-17: -0.19 +/- 0.21 parts per thousand, and pegmatite GSR-18: 1.35 +/- 0.10 parts per thousand.

Automated summary

This study presents a high-precision analytical method for lithium isotopic analysis using a modified chemical purification procedure and optimized instrumental setup. The method achieves a high precision of +/- 0.13 to 0.23 parts per thousand based on repeat measurements of Li standard and geological reference materials. Factors causing instrumental mass fractionations, such as Li concentration mismatch and the Na matrix effect, are also evaluated. The study reports the delta Li-7 values of eight international reference materials and introduces seventeen Chinese geological reference materials.