Raman Spectroscopic Identification of Calcium-Oxalate-Type Kidney Stone

The Raman scattering technique is used to obtain spectra from four kidney stones. An argon-ion laser (514.5 nm) is focused directly on the surface of the stones. Three stones were known to be composed mainly of hydrates of calcium oxalate, CaC₂O₄·H₂O, and CaC₂O₄·2H₂O. The scattered Raman shift is examined and compared with that of the standard hydrates. Two stones have spectra almost identical to that of calcium oxalate monohydrate. The characteristic bands at 1465 and 1492 cm⁻¹ are easily observed. The spectrum from the third stone shows a band at 1477 cm⁻¹ characteristic of calcium oxalate dihydrate, but it also shows weaker bands at 1465 and 1492 cm⁻¹, which are observed in spectra of calcium oxalate monohydrate. It is concluded that the first two stones are primarily composed of CaC₂O₄·H₂O, while the third stone includes both hydrates in its structure. The fourth stone, from a Russian woman, shows bands at 627, 998, 1038, 1405, 1465, and 1492 cm⁻¹. The first few bands are characteristic of uric acid, while the 1465- and 1492-cm⁻¹ bands indicate calcium oxalate monohydrate. It is possible not only to identify these two components but also to show their relative distribution within the stone.