Raman Spectroscopic Identification of Phosphate-Type Kidney Stones

Phosphate-type kidney stones have been examined by the Raman spectroscopic technique by merely focusing laser light on the cut surface of the stones. Before examination of the kidney stones, Raman spectra of several standard phosphate compounds—such as calcium monobasic phosphate [Ca(H 2 PO 4 ) 2 ], calcium dibasic phosphate (CaHPO 4 ), calcium tribasic phosphate [Ca 10 (PO 4 ) 6 (OH) 2 ], calcium orthophosphate [Ca 3 (PO 4 ) 2 ], brushite (CaHPO·2H 2 O), struvite (MgNH 4 PO 4 ·6H 2 O), and hydroxyapatite [Ca 10 (PO 4 ) 6 (OH) 9 ]—were obtained. Hydroxyapatite has a distinctive line at 961 cm −1 , and one kidney stone examined showed a comparable band. It was concluded that one stone is primarily hydroxyapatite and another one is brushite. The analysis of the kidney stones by Raman spectroscopy is direct, fast, and nondestructive, and does not require tedious sample preparation.