Development and optimization of microbeam X-ray fluorescence analysis of Sr in speleothems

• μ-XRF is a rapid, non-destructive technique of obtaining Sr values in speleothems.
• μ-XRF provides comparable results to other methods.
• Analytical uncertainty is shown via statistical analysis of an experimental dataset.

Trace-metal abundances and ratios (Sr/Ca, Mg/Ca, Ba/Ca) in speleothems can be indicators of the hydrogeochemical processes active in overlying epikarst and serve as valuable proxies for precipitation amount and source, water residence time, and vegetation cover. However, conventional methods of trace element acquisition can be expensive, time-consuming, and destructive. A semi-portable μ-XRF system is compared to other methods, as it is non-destructive, rapid, and has the capacity to provide high quality datasets. A suite of test scans was performed in order to define the appropriate methodology for the application of μ-XRF in trace metal analysis of speleothems. Statistical analyses were performed on an experimental dataset in order to assess the precision with which data were obtained and determined that there is no evidence for time-dependent behavior within the data and there is no evidence that the data do not follow a Poisson distribution. The optimal count time varies from sample to sample, as it was determined to be a function of the desired level of analytical uncertainty.Sr results for a speleothem obtained through LA-ICP-OES show a high degree of comparability to results obtained through μ-XRF and demonstrate the suitability of this non-destructive method. Sr counts can also be converted to concentration [ppm] via X-ray-tube-dependent calibration curves.