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

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 30 h-’ 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.