EDTA Titration of Calcium and Magnesium

Abstract

The revised method for the EDTA titration of calcium and/or magnesium in pharmaceutical preparations and canned whole tomatoes, adopted as official, first action last year, was studied collaboratively again this year. Two simulated pharmaceutical mixtures and two samples of tomato juice were analyzed by 13 analysts in 12 laboratories. The results were easily reproducible, and the agreement between laboratories was good. The required use of a pH meter in all pH adjustments has eliminated most of the turbidity and fading end points; occasional turbidity or fading end points are due to faulty or improperly prepared resin that does not completely remove phosphates. Because the revised method gives continuing precision and low standard deviations, it is recommended for adoption as official, final action.