Abstract: 1-Hydroxyethylidene-1,1-diphosphonic acid (HEDP) is usually used as a scale and corrosion inhibitor in recycle-cooling water for steel industry. The quick and accurate analysis of HEDP concentration in water is of importance to control the inhibitor adding program. However, the common method for HEDP analysis, which determines the total phosphate in water samples, may suffer the serious problem of incorrectly including degraded HEDP as the active HEDP reagent. In this study, the method of  the determination of HEDP in recycle-cooling water by ion chromatography was investigated. The chromatographic parameters, including elution and detection, were optimized. The separation was achieved on an IonPac AS14A column with NaOH solution of 80 mmol/L as the eluent at a flow rate of 1.0 mL/min, and the detection was performed by a suppressed conductivity detection mode with the injection volume of 25 μL. The method showed good linearity within the range of 0.25 and 25 mg/L with an average recovery of 102%. The detection limit of the method reached as low as 0.1 mg/L. The relative standard deviations for 0.25 and 0.5 mg/L HEDP standard solutions were 4.7% and 3.5% (n=13), respectively. The method has been applied for the determination of HEDP in recycle-cooling water samples with the advantages of being simple, fast, sensitive, and interference free.

Key words: 1-hydroxyethylidene-1,1-diphosphonic acid, recycle-cooling water , ion chromatography (IC)