Journal of Chromatography A, 661 (1994) 245-248 Elsevier Science B.V.. Amsterdam CHROMSYMP. 2935 Simultaneous determination of benzotriazole copper inhibitor and microbiocidal isothiazolinenones by high- performance liquid chromatography A. Iob*, F. Al-Yousef, B.S. Tawabini, A.I. Mohammed and N.M. Abbas Research Institute, King Fahd University of Petroleum and Minerals, Dhahran 31261 (Saudi Arabia) ABSTRACT 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 isothiazolinenones had A,,, at 275 nm, so an HPLC method was sought. Optimum conditions were established using a Hewlett-Packard RP C, column to be methanol-water (4060) containing 0.05 M KH,PO, 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. INTRODUCTION Sodium benzotriazole (BZTR) and its deriva- tives are commonly used as copper inhibitors in coolant additives and as light stabilizers in photo- graphic films and 2-methyl-4-isothiazoline-3-one (MIS) and 5-chloro-2-methyl-4-isothiazoline-3- one (CMIS) are extensively used as microbioci- da1 agents, disinfectants, etc., in cooling waters (chilling water). Mixtures of these products at certain levels are use,d in a large water-chilling plant in Saudi Arabia. This chilling plant serves as a cooling facility for a city which encompasses residential areas (~5000 apartments), schools and a local hospital. This facility needs rigorous maintenance procedures and additives are in- corporated at the required concentration levels on a constant basis. Some of the common addi- tives needed include dispersants, corrosion in- hibitors and pH adjusters in addition to the * Corresponding author. copper inhibitors and microbiocidal mixture. The latter two are mainly used in the “closed-loop” water-chilling compressor section. The specifica- tion regarding these two additive solutions are sodium benzotriazole 20.1% and isothiazolinone mixture ~1.5% (usually the 5-chloro product predominates, i.e., cu. 1.15% with the other compound at 0.35%). Having these additives at the specified concen- trations is critical for the proper maintenance of the chilling plant and a method had to be developed to monitor the concentrations of all the additives. Several methods have been re- ported for the determination of isothiazolinones in variety of matrices, e.g., HPLC and UV detection [l-3], spectrophotometric evaluation after reductive cleavage [4] and iodimetric de- termination after ring opening with NaHSO, [5]. Several HPLC techniques used for determination of benzotriazole and its derivatives have also been published [6-111 and have been used for the evaluation of benzotriazole in ethylene glycol coolants, photographic products, etc. However, 0021-9673/94/$07.00 0 1994 Elsevier Science B.V. All rights reserved SSDI 0021-9673(93)E0942-N