Abstract: This article told us a new potentiomtery that used the calcium ion selective electrode as the indicating electrode,saturated mercury chloride electrode as the reference electrode and EGTA standard solution as the titration reagent to assay the content of calcium ion in the muddy and color drinks.The end-point of titration could be deterrmined by the potential break.The method was simple,sensitive and accurate.The relative standard deviation of calcium milk was 0 11% and that of fruit juice was 2 1%.The recovery Percent of added standard sample of calcium milk was 99%～100%,and that of fruit juice was 102%～105%.It could also be used to directly determinate the content of calcium ion in the muddy and color liquid.

Key words: Calcium, Calcium ion selective electrode, Potentiometril titration