Solubility product of OH-carbonated hydroxyapatite.
Information on the solubility of OH-carbonated hydroxyapatite, Ca10(PO4)6(CO3)x(OH)2-2x, previously has not been available. In the present study the solubility product (Ksp) of OH-carbonated hydroxyapatite was measured in a 0.1 M acetic acid and sodium acetate buffer solution in a pH range of 4.0-5.8 at a CO2 partial pressure of 10(-3.52) atm. The equilibrium solubility increased with the increase of carbonate content. The Ksp values decreased with the decrease of pH. For example, Ksps were 10(-119), 10(-123), and 10(-130) for pure hydroxyapatite at pH 4.9, 4.5, and 4.1, respectively. The decrease of Ksp was not accounted for by calcium-carbonate complexation. Ksp measured at isoelectric points (L) was expressed as pL = 118.65 - 0.47316 x (CO2 wt%)2.4176. From this formula, the L values were calculated for pure and fully carbonated hydroxyapatite as 10(-118.7) and 10(102.8), respectively. The L value for pure hydroxyapatite agreed with values measured under carbonate-free conditions. Therefore, the L values were regarded as the Ksp for OH-carbonated hydroxyapatite excluding errors arising from carbonate contamination in the solution.
Ito
A
A
National Institute for Advanced Interdisciplinary Research, MITI, Ibaraki, Japan.
Maekawa
K
K
Tsutsumi
S
S
Ikazaki
F
F
Tateishi
T
T
D000399:Air Pressure; D001862:Bone Resorption; D002245:Carbon Dioxide; D017886:Durapatite / Q000737:chemistry*; D005110:Extracellular Space / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007525:Isoelectric Focusing; D009584:Nitrogen; D012044:Regression Analysis; D012995:Solubility
D002245:Carbon Dioxide; D017886:Durapatite; D009584:Nitrogen