title: Effect of citrate and pyrophosphate on the stability of calcium oxalate dihydrate.
abstract: The effect of citrate and pyrophosphate on the stability of calcium oxalate dihydrate (COD) was studied in an aqueous solution over 7 days. COD was precipitated from 1.0 x 10(-2) mol/l calcium oxalate solution with the addition of citrate and/or pyrophosphate and separated by centrifugation immediately, 48 h and 7 days after the precipitation. The percentage of COD in the precipitate, determined by X-ray diffraction, increased with a rise in citrate or pyrophosphate concentration and reached > or =90% at a citrate concentration of 1.0 x 10(-3) mol/l or a pyrophosphate concentration of 2.0 x 10(-4) mol/l. The resulting COD was completely transformed into calcium oxalate monohydrate within 48 h when the precipitate was composed of <90% COD. Nearly pure COD produced with pyrophosphate was stable over 7 days while that with citrate underwent partial transformation within 48 h. An additive effect of citrate and pyrophosphate was found on the stability of COD. It was concluded that a pyrophosphate concentration above a critical point was sufficient to prevent solution-mediated transformation of COD, and this critical point might be lowered to the physiological range with the presence of citrate.
authors.affiliation: Department of Urology, Jichi Medical School, Tochigi-ken, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Yuzawa
authors.forename: K
authors.initials: K
authors.lastname: Tozuka
authors.forename: A
authors.initials: A
authors.lastname: Tokue
mesh_terms: D002129:Calcium Oxalate / Q000737:chemistry*; D011232:Chemical Precipitation; D019343:Citric Acid / Q000737:chemistry; D003460:Crystallization; D011756:Diphosphates / Q000737:chemistry; D004355:Drug Stability; D006801:Humans; D066298:In Vitro Techniques; D008855:Microscopy, Electron, Scanning; D010316:Particle Size; D012996:Solutions; D014545:Urinary Calculi / Q000737:chemistry*; D014961:X-Ray Diffraction
chemical_list: D011756:Diphosphates; D012996:Solutions; D002129:Calcium Oxalate; D019343:Citric Acid