The systematic error in photometric set-point titrations of submicromolar amounts of calcium and zinc

Although reproducible results can be obtained in photometric set-point titrations of submicromolar amounts (5·10^?5 M and higher) of calcium(II) and zinc(II) by using an automatic titrator, the systematic error can be considerable. This error is partly intrinsic in nature, but there is an additional error caused by dilution in successive titrations. Accurate values can be obtained only when standardization and actual titrations are performed under the same conditions of dilution, set-point, indicator concentrations, etc.