Schott H
J Pharm Sci. 1977 Nov;66(11):1548-50. doi: 10.1002/jps.2600661111.
The zero point of charge (ZPC) of slightly soluble compounds is the pH at which their particles suspended in water have zero charge. The ZPC values of slightly soluble hydroxides were compared with their solubility product in the form of its negative logarithm, pKSP, and with th pH of their suspensions in pure water, pHSP, which is a function of pKSP. The ZPC-pKSP relation was nonlinear while the ZPC-pHSP relation was linear. Either equation can used to estimate the ZPC value of a hydroxide from its solubility product. The ZPC of a given hydroxide was higher than its pHSP because polyvalent cations are more extensively adsorbed and less extensively desorbed from the particle surface than the monovalent hydroxide ion. At the pHSP, there are equivalent amounts of the cation and of the hydroxide anion in solution, but the surface layer of the hydroxide particle contains an excess cation on an equivalent basis. This imbalance confers a positive charge to the particle. The solubility product of aluminum hydroxide, redetermined at 25 degrees by means of pH measurements, was 8 X 10(-33). Its ZPC, redetermined by microelectrophoresis, was 8.5 +/- 0.1.
微溶化合物的零电荷点（ZPC）是指其悬浮于水中的颗粒电荷为零时的pH值。将微溶氢氧化物的ZPC值与其以负对数形式表示的溶度积pKSP以及其在纯水中悬浮液的pH值（pHSP，它是pKSP的函数）进行了比较。ZPC与pKSP的关系是非线性的，而ZPC与pHSP的关系是线性的。这两个方程均可用于根据氢氧化物的溶度积估算其ZPC值。给定氢氧化物的ZPC高于其pHSP，因为多价阳离子比单价氢氧根离子更广泛地吸附在颗粒表面且更难从颗粒表面解吸。在pHSP时，溶液中阳离子和氢氧根阴离子的量相等，但氢氧化物颗粒的表面层在等量基础上含有过量的阳离子。这种不平衡赋予颗粒正电荷。通过pH测量在25℃重新测定的氢氧化铝的溶度积为8×10⁻³³。通过微电泳重新测定的其ZPC为8.5±0.1。
