Solubility of the Three Calcium Oxalate Hydrates in Sodium Chloride Solutionsand Urine-Like Liquors

Abstract

Calcium oxalate forms three hydrates (stable monoclinic mono-hydrate (COM), metastable tetragonal dihydrate (COD) and triclinic trihydrate (COT)), which are of medical importance in urinary calculi formation. In this work, the solubility of these calcium oxalate hydrates was determined at 20, 25, 30, 37, and 40 C in aqueous NaCl (0.02±0.20 mol Á dm À3 ) and in urine-like liquors. Also, for the ®rst time, the solubility of COM was systematically studied as a function of pH in arti®cial urine solutions which contain organic compounds. The concentrations of calcium ions were measured continuously using a calcium ion selective electrode and also determined by AAS. The thermodynamic solubility products were obtained from computer simulations in which all possible complexes formed in aqueous solution were taken into account. These values were compared to those available in the literature; it was found that the present results, especially for COD and COT, constitute a major improvement on the previously reported values. The constants determined in this work were used to predict the solubility of calcium oxalate hydrates at different pH in urine-like liquors. It was found that in arti®cial urine solutions, citrate and magnesium ions promote the solubility of COM, whereas urea and creatinine have no signi®cant effect. Lo Èslichkeit der drei Calciumoxalathydrate in Natriumchloridlo Èsungen und urina Èhnlichen Flu È ssigkeiten Zusammenfassung. Calciumoxalat bildet das stabile monokline Monohydrat (COM) sowie zwei metastabile Phasen, das tetragonale Dihydrat (COD) und das trikline Trihydrat (COT). Da die drei Calciumoxalathydrate bei der Entstehung von Nierensteinen eine wichtige Rolle spielen, wurde ihre Lo Èslichkeit bei 20, 25, 30, 37, und 40 C in NaCl-Lo Èsungen (0.02±0.20 mol Á dm À3 ) sowie in ku Ènstlichen Urinlo Èsungen, die zum Teil auch organische Substanzen enthielten, gemessen. In letzteren wurde die Lo Èslichkeit von COM als Funktion des pH-Werts erstmalig systematisch untersucht. Die Ca 2 -Konzentrationen wurden mit Hilfe einer ionenselektiven Elektrode sowie durch AAS bestimmt. Die thermodynamischen Lo Èslichkeitsprodukte wurden aus Computersimulationen erhalten, in denen die in der wa Èûrigen Lo Èsung vorkommenden Komplexe weitestgehend à Corresponding author beru Ècksichtigt wurden. Beim Vergleich dieser Gro Èûen mit Literaturwerten stellte sich heraus, daû insbesondere die Werte fu Èr COD und COT eine wesentliche Verbesserung gegenu Èber den bisherigen Daten darstellen. Die in dieser Arbeit ermittelten Lo Èslichkeitsprodukte wurden zur Berechnung der Lo Èslichkeit der Calciumoxalathydrate in ku Ènstlichem Urin verwendet. Es zeigte sich, daû Mg 2 und Citrat die Lo Èslichkeit erho Èhen, wogegen Harnstoff und Creatinin keine signi®kante Auswirkung haben.

Pseudo‐polymorphic Behavior of Precipitated Calcium Oxalate

“…Values for the solubility product at 20 C were taken from Streit, Tran-Ho and Königsberger [5] and can be found in Tab. 1.…”

Kinetic study of dehydration of calcium oxalate trihydrate

“…Calcium oxalates were up to now frequently studied as chemicals involved in formation of urinary calculi [5,6], main attention is paid to finding the factors and conditions giving support to calcium oxalate and consequently to kidney stone formation [7,8]. The most frequently published data on calcium oxalate describe the crystal growth (conditions and kinetics) [3,[9][10][11][12][13][14][15][16][17][18] and dissolution of hydrates [19][20][21][22]. The crystallization of COM has been the subject of physico-chemical and biological analyses [23,24].…”

Structure and Composition of Non-Infectious Phosphate Calculi Formed in Patients with Low and High Urinary Phosphate Concentrations

“…− Speciation of oxalate, using the dissociation constants for oxalic acid [16], showed that most of the oxalate in urine of both groups was present only as the anion Ox solubility product of calcium oxalate monohydrate (8.65 mol 2 /L 2 [17]), we found that the supersaturation of urine with cal-cium oxalate monohydrate (COM) was 1.8 for group I and 8.0 for group II.…”

“…The urine of both groups of calculi was highly supersaturated with hydroxyapatite, making this the major component of each stone. Although the average urine in groups I and II was supersaturated with both COM and COD, since the solubility product of these compounds is very similar [17], CaOx was present only in group II calculi. This may be due to fractional precipitation, in that the less soluble compound, hydroxyapatite, precipitates prior to the more soluble compounds, COM and COD.…”