A simultaneous evaluation method of purity and apparent stability constant of Ca-chelating agents and selectivity coefficient of Ca-selective electrodes.
To determine the purity (q) of Ca-chelating agents (such as EGTA and BAPTA) and their apparent stability constants to Ca2+ (K') using Ca(2+)-selective electrodes precisely, we have developed a new method using the double-log optimization. Free Ca2+ concentration was plotted against the ratio of the concentrations of Ca(2+)-bound to Ca(2+)-free chelator on double logarithmic co-ordinates in which a linear relationship with a slope of -1 must hold for the metal-chelator reaction with a stoichiometry of 1 to 1. Not only the q and K' values but also the selectivity coefficient of the electrode could be simultaneously estimated on the double-log plot through an optimizing method. Error analyses using a Monte Carlo simulation showed that the double-log plot is statistically more reliable and robust than the Scatchard plot and that the optimizing method is more objective and reliable than previous methods involving extrapolation and truncation procedures.
Oiki
S
S
Department of Cellular and Molecular Physiology, National Institute for Physiological Sciences, Okazaki, Japan.
Yamamoto
T
T
Okada
Y
Y
D002118:Calcium / Q000032:analysis*; D002614:Chelating Agents / Q000737:chemistry* / Q000302:isolation & purification*; D003627:Data Interpretation, Statistical; D004355:Drug Stability; D017736:Ion-Selective Electrodes / Q000592:standards*; D008956:Models, Chemical
D002614:Chelating Agents; D002118:Calcium