In situ Sr-Nd Isotopic Measurement of Apatite Using Laser Ablation Multi-collector Inductively Coupled Plasma-Mass Spectrometry

Apatite is a common accessory mineral, having a high Sr-Nd content and a low Rb content. The precise determination of micro-area Sr-Nd isotopic composition for apatite will provide important geochemical information for discussing the details of the geological process. Laser Ablation Multi-collector Inductively Coupled Plasma-Mass Spectrometry (LA-MC-ICPMS) technique has the characteristics of rapid analysis, high analytical precision and high spatial resolution, and is particularly suitable for Sr-Nd isotopic analysis of a large quantity of fine-grained apatite samples. The precise deduction of isotopic interference and calibration of instrument mass bias are crucial for in-situ analysis to obtain Sr-Nd isotopic ratio. In this article a method is described, which adopts LA-MC-ICPMS and combines with the newly published method for deduction of interferences, like Kr, Rb, divalent ions of REEs and calcium-containing polymer for Sr isotopes, Sm for Nd isotopes. The calibration of instrument mass bias is carried out, and the in-situ Sr-Nd isotopic analysis approach for apatite is established. The test results of Durango apatite standard, Apatite 1 and PE show that Sr-Nd isotopic composition of apatite sample with high Sr-Nd content can be accurately determined. The specific results are consistent with literature or the measured values by Thermal Ionization Mass Spectrometry (TIMS) within error. The measurement precision of Sr isotopes is < 0.015% (2SD), and that of Nd isotopes is < 0.005% (2SD). The established method is applied for Sr-Nd isotopic analysis of Durango apatite standard, Apatite 1 and PE (laboratory standard), respectively. The analysis results indicate that the Sr-Nd isotopic compositions of the three apatite samples are basically consistent, and can serve as ideal reference samples for in-situ Sr-Nd isotopic analysis.