Surface-tension titration of calcium(II) and manganese(II) by using triethanolamine as masking reagent

Department of Chemistry, Faculty of Science, Hokkaido University, Sapporo 060, Japan point, the surface tension jumps to almost the initial value, due to the reaction of the liberated calcium ion with palmitate ions to form the sparingly soluble salt. The difference of the amount of the titrant required until the second end-point from the first corresponds to the amount of manganese(II). A serious interference by iron(III) with the determination of manganese(II) is found, probably because a part of the iron(III)-TEA complex is reduced to its divalent state with hydroxylamine, the iron(II) complex reacting with EDTA.