Arsenazo III as metallochromic indicator for complexometric determination of calcium in slightly alkaline medium.

Arsenazo III is proposed as metallochromic indicator for calcium in slightly alkaline medium. The visual titration with EDTA was performed at pH 8 and 40 microg-12 mg of calcium were determined. The interference of some ions was considered and it was found that phosphate does not interfere appreciably. Spectrophotometric detection of the end-point was used for titration of calcium in the presence of magnesium at pH 9. For the estimation of the titration error, the conditional stability constants of the calcium-arsenazo III complex were found.