Simultaneous determination of benzotriazole copper inhibitor and microbiocidal isothiazolinenones by high-performance liquid chromatography

A high-performance liquid chromatographic (HPLC) procedure for the separation and determination of the components of a formulation that contained sodium benzotriazole (copper inhibitor), 2-methyl-4-isothiazoline-3-one and 5-chloro-2-methyl-4-isothiazoline-3-one (microbiocide mixture) was developed. This mixture is used to protect and maintain a large water-chilling plant in Saudi Arabia. A UV spectrophotometric method was tried unsuccessfully as both sodium benzotriazole and the isothiazolinones had λ_max at 275 nm, so an HPLC method was sought. Optimum conditions were established using a Hewlett-Packard RP C₈ column to be methanol-water (40:60) containing 0.05 M KH₂PO₄ as the eluent at a flow-rate of 1 ml/min. The relative standard deviation of the method at the 95% confidence level was found to be 0.8, 0.7 and 2.4% for the respective components at concentration levels of 35, 115 and 50 mg/l, respectively.