Application of three data evaluation methods for in situ iron isotope analysis using the ns-LA-MC-ICP-MS technique

To investigate performances of different data evaluation methods in terms of accuracy and precision for in situ Fe isotope analysis, the reference glass BHVO-2G is analyzed in both line scan and spot analysis modes using a nanosecond laser ablation system coupled to multi-collector inductively coupled plasma mass spectrometry (ns-LA-MC-ICP-MS). Three data processing methods, i.e., the individual data points method, the linear fitting method and the section integration method, are applied to evaluate Fe isotope ratios from single analyses. delta Fe-56 and delta Fe-57 values obtained from the three methods are in excellent agreement with the published results, with analytical uncertainties (2SD) of 0.12-0.13 parts per thousand for delta Fe-56 and 0.19-0.22 parts per thousand for delta Fe-57, suggesting their practicability for the Fe transient signal. However, the linear fitting method exhibits slightly poorer reproducibility in comparison with the other two because the fitting slope may be more sensitive to the distribution of ablation data points with high intensities. Both the individual data points and section integration methods show highly consistent results with each other, thus are equally capable of in situ Fe signal processing. The spot analyses with significant signal decline during ablation yield analytical uncertainties approximately double those of line scan. When selecting ablation intervals with different lengths within the line scan signal range, it is observed that the intervals selected from the start of the ablation process can be shortened to 60 s or less, corresponding to a <= 60 mu m ablation line on the sample surface, to yield decent accuracy and precision.