Color-fading Photometric Determination of Calcium in Drugs

A stable complex was formed by the reaction of Ca2+ with the color reagent,picramine CA in an ammoniacal buffer medium of pH 11. Influential factors,including the pH and amount of buffer solution,amount of color reagent,time of reaction,and interferences of co-existing ions were studied and optimized. Linear relationship between the magnitude of decrease in absorbance of the color reagent and the mass concentration of Ca2+ was obtained in the range of 0.32-3.60 mg·L-1,and value of apparent molar absorptivity found was 1.26×104L·mol-1·cm-1 when measured at the wavelength of 590 nm. The proposed method was used in the determination of Ca2+ in drugs,the results obtained were checked quite well with those found by EDTA titrimetry,and values of RSD′s (n=10) found were in the range of 1.5%-2.1%.