New prospects to the multi-elemental analysis of single microcrystal of apatite by total-reflection X-ray fluorescence spectrometry

Highlights: • New TXRF method for the analysis of single microcrystal of apatite is developed. • Nitric acid digestion of the single apatite microcrystal on the carrier. • Phosphorous stoichiometric value is used as the internal standard. • The trueness of TXRF is assessed by the analysis of Durango and Otter Lake. • TXRF results were compared to LA-ICP-MS method. The elemental analysis of apatite minerals is an important study that is utilized in several applications in geology, biology, medicine, agriculture, technology, and environmental remediation. Laser ablation inductively coupled mass spectrometry (LA-ICP-MS) is a routine method for the elemental analysis of apatite microcrystals in geological applications. In this study, we propose a new method for the analysis of single grain of apatite with a mass of a few μg using total-reflection X-ray fluorescence spectrometry (TXRF), which is faster, cheaper, and easier in quantification procedure than LA-ICP-MS. The direct preparation of the single apatite microcrystal on the quartz carrier using nitric acid digestion and quantification using the stoichiometric value of P as an internal standard allows to obtain the major, minor, and trace elements (from K to U) simultaneously. For the choice of the internal standard in TXRF, the Raman spectroscopy is applied to obtain the information of the mineral phases and their distribution formed in the apatite sample after the digestion procedure. Validation of the proposed TXRF method is conducted by the analysis of reference materials (Durango and Otter Lake) and comparison of results with the TXRF for bulk-type of apatite and LA-ICP-MS methods.