X-ray powder diffraction used as a tool to investigate kidney calculi stones

Abstract

The X-ray powder diffraction (XRPD) technique was used to study the phase composition of human renal calculi. The stones were colleted from 56 donors of Vit´oria City, Esp´ırito Santo State - southeast - Brazil. A XRD phase quantification reveals that 61% of the studied renal stones are composed exclusively by calcium oxalate (34% formed only by calcium oxalate monohydrate and 27% presents on both monohydrate and dihydratate calcium oxalate). The 39% multi composed calculi have various other phases such as uric acid and calcium phosphate. An investigation of XRD data of one apparent monophasic (COM) renal calculus revealed the presence of a small amount of hydroxyapatite. The presence of this second phase and the morphology of the stone (ellipsoidal) indicated that this calculus can be classified as non-papillary type and its nucleation process developed in closed kidney cavities. A study of the phase transformation of monohydrate calcium oxalate into calcium carbonate CaCO3 was carried out by annealing of a monophasic monohydrate calcium oxalate calculi at 200, 300, and 400 Celsius temperatures during 48 hours in a N2 gas atmosphere. It was concluded that X-ray powder diffraction can be used as suitable technique to study the composition and phase diagram of renal calculi.