Flow-Injection Determination of the Total Water Hardness by Using a Copper(II) Ion-Selective Electrode and a Copper(II) Ion Buffer

Abstract

A potentiometric determination of the total water hardness by flow-injection analysis is proposed, which uses both a Cu²⁺ ion-selective electrode detector and a Cu²⁺-ion buffer stream comprising a Cu-EDTA complex and free EDTA. This method is based on potentiometric monitoring of the change in the free Cu²⁺-ion concentration in the buffer with a Cu²⁺ ion-selective electrode, caused by the reaction of Ca²⁺ and Mg²⁺ ions with free EDTA in the buffer. Chloride interference in the measurement of the Cu²⁺-ion concentrations with the Cu²⁺ ion-selective electrode was successfully eliminated by adding triethylenetetramine to the Cu²⁺-ion buffer. The total hardness of seawater samples could therefore be determined at a sampling rate of 30h^-1 and a relative standard deviation of 0.7%. The obtained results using the proposed method were in good accord with those obtained by conventional chelatometric titration.