A novel pH-sensitive method for the quantification of Ca 2+ ions by complexometric titration with Na 3 HEDTA.

A simple and accurate complexometric titration has been developed by the reaction between Ca ²⁺ ions (pH 7) and Na ₃ HEDTA (pH 11) solutions. Formation of a Ca-EDTA complex and release of H ⁺ ions in the system were traced by a decrease in the pH. At the equivalence point of the titration, a sharp increase in the pH was observed. Looking at the working pH range (pH 6.2-7.5) of this method, another complexometric titration method has been developed by using bromothymol blue as a pH sensitive indicator. This is the first report of a complexometric titration by using an acid base indicator.