Determination of Serum Calcium by Means of Orthocresolphthalein Complexone

Abstract

Under alkaline conditions, the metallochromic dye orthocresolphthalein complexone (OCPC; phenolph-thalein, 3[image], 3[image] bis-{ [ bis-(carboxymethyl) amino] methyl} -5[image], 5[image]-dimethyl forms a colored complex with both Ca and Mg, the absorbance of which is maximum at 570 mu. The response of the dye to Mg is completely suppressed by incorporating an optimum amount of 8-quinolinol in the OCPC color reagent. Two procedures are described. Calcium is freed from combination with serum proteins by means of deproteinization. An aliquot of this extract is added to the OCPC color reagent and the absorbance due to Ca is measured. In the second procedure Ca is isolated directly from the serum as the insoluble oxalate which is dissolved in 0,2 N HCl and added to the OCPC color reagent. The results of each method are compared.