Automatic Determination of Water Hardness by Vector Colorimetry with Acid Chrome Blue K

Based on the Mg2 + complexation with acid chrome blue K (ACBK) at pH 10.2, an automatic system was designed to determine total hardness of water. The system consists of a vector colorimeter, a multi-channel sampling pump and both reagents A and B. Two kinds of reagent solutions were prepared and used in this system, i.e., ammoniacal buffer and ACBK-disodium magnesium EDTA solutions. The experimental results of the standard solutions containing 2 and 3 mg/L of total hardness showed that the relative standard deviations (RSDs) were 1.9% and 2.2%, respectively, and the limit of detection (LOD) was only 0.035 mg/L. The detection of four natural water samples showed that the recoveries were between 85.0% and 108.6%, consistent with those obtained by ICP-AES method.