Analytical feasibility of a new reference material (IRMM-524A Fe metal) for the in situ Fe isotopic analysis of pyrite and ilmenite without matrix effects by femtosecond LA-MC-ICP-MS

Abstract

Nowadays, in situ Fe isotopic analysis is facing a dilemma that the conventional reference material of IRMM-014 for isotope ratio normalization is commercially unavailable and is unable to meet the needs of laboratories. In this study, the other Fe metal (IRMM-524A), instead of the nearly exhausted IRMM-014, has been systematically checked to be a potential reference material for the Fe isotopic analysis by femtosecond laser ablation multi-collector inductively coupled plasma mass spectrometry (fs LA-MC-ICP-MS). A total of 136 analyses on IRMM-524A were directly calibrated against IRMM-014 using fs LA-MC-ICP-MS during eight analytical sessions. The result shows that the IRMM-524A Fe metal is relatively homogeneous, with average values of 0.01 ± 0.13‰ and −0.02 ± 0.19‰ (2SD, n = 136) for δ⁵⁶Fe and δ⁵⁷Fe, respectively, which are identical to the published values obtained by solution nebulizer (SN)-MC-ICP-MS within analytical uncertainties. Fe isotopic compositions of two in-house standards (Balmat pyrite, PZH12-24 ilmenite) and four natural samples (NKAu01 pyrite, PZH12-16 ilmenite, PZH12-18 ilmenite, and Moosilauke ilmenite) measured by fs LA-MC-ICP-MS relative to IRMM-524A or IRMM-014 are identical within analytical uncertainties. In addition, five of the samples (Balmat pyrite, PZH12-24 ilmenite, NKAu01 pyrite, PZH12-16 ilmenite, and PZH12-18 ilmenite) have homogeneous Fe isotopic compositions and yield an external reproducibility of 0.12‰ to 0.16‰ for δ⁵⁶Fe values for different sections within three years. Thus, the IRMM-524A Fe metal and other five samples can be used as reference material and secondary standards for quality assurance for non-matrix-matched Fe isotopic analysis of pyrite and ilmenite by fs LA-MC-ICP-MS.