Dinjus U, Klinger R, Wetzker R
Biomed Biochim Acta. 1984;43(10):1067-72.
We prepared a series of Ca/EGTA solutions and compared the pCa2+free values obtained by calculation and measurement with an ion sensitive electrode. Two possible reasons for the discrepancies between these values were studied: (1) the effect of various association constants used for the calculation of pCa2+free, and (2) the influence of deviations of the calcium total concentration in the Ca/EGTA solutions from the values used for the calculation. The results obtained showed that the main reason for differences between calculated and measured pCa2+free values was the nonequimolarity of both stock solutions CaCl2 and EGTA. A linear dependence of measured electrode potentials with Nernstian behaviour on the calculated pCa2+free in the Ca/EGTA solutions has been obtained with carefully equalized stock solutions.
我们制备了一系列钙/乙二醇双四乙酸（Ca/EGTA）溶液，并将通过计算得到的游离钙离子浓度（pCa2+free）值与用离子敏感电极测量得到的值进行了比较。研究了这些值之间差异的两个可能原因：（1）用于计算游离钙离子浓度的各种缔合常数的影响，以及（2）Ca/EGTA溶液中钙总浓度与计算所用值的偏差的影响。所得结果表明，计算得到的和测量得到的游离钙离子浓度值之间存在差异的主要原因是氯化钙（CaCl2）储备溶液和乙二醇双四乙酸（EGTA）储备溶液均非等摩尔。使用精心调配使浓度相等的储备溶液，已获得了测量电极电位与Ca/EGTA溶液中计算得到的游离钙离子浓度之间呈能斯特行为的线性关系。
