Determination of Total Hardness in Water by Visible Spectral Titration

A method of determination of total hardness in water by visible spectral titration was proposed. During the entire titration process, the real color measurement system was used to replace human sensory judgment, and the color change titration curve was established between spectral measurement parameters and reagent quantity. The abrupt peak on the curve was used to identify the titration endpoint or structural change point. Visible spectral titration could overcome the difficulties of sensory titration, such as the disunity of color evaluation conditions, the inconsistency of individual physiological conditions of operators, and the inability to trace the value, and it could realize the automation of measurement. The above method was applied to determination of total hardness of water quality standard samples, and it was shown that the determined values were within the uncertainty range of the certified values of the standard samples. Test for recovery was made on the actual samples by the standard addition method, giving results in the range of 99.7%-101%. The total hardness of 8 water samples was determined by visible spectral titration and visual titration (EDTA complexometric titration), respectively. As found by the paired t-test results, there was no significant difference in the determination results between the two methods.