Investigation of the occurrence and sources of calcium (Ca) in urinary stones using synchrotron radiation based X-ray fluorescence and X-ray absorption spectroscopy (XAS)

Abstract

The distribution and occurrence of calcium in different types of urinary stones were investigated using synchrotron radiation micro X-ray fluorescence (SR-µXRF), total reflection X-ray fluorescence (TXRF), and X-ray absorption spectroscopy (XAS). For this purpose, polished cross sectional areas of different urinary stones were prepared, and the elemental mapping of Ca and other related elements was performed. The elemental speciation of Ca was also investigated using X-ray Absorption Spectroscopy (XAS) including X-ray Absorption Near Edge Structure (XANES) and the Extended X-ray Absorption Fine Structure (EXAFS). The XANES results indicate the predominant existence of different ratios of calcium oxalate monohydrate (CaC₂O₄·H₂O) and alpha tri-calcium phosphate (Ca₃(PO₄)₂, α-TCP). The distinct features observed in the R-space of the EXAFS spectra reflect variations in the Ca–O bond lengths. These differences indicate changes in the local chemical environment, suggesting the presence of multiple calcium compounds in the urinary stones. The obtained results could provide more insight into calcium metabolism and calcium homeostasis in urinary stones. The calcium crystallization in the urinary tract could originate from abnormal processes or dysregulation of calcium in urine and urinary stones.