Research Article Received: 7 February 2008, Revised: 19 March 2008, Accepted: 19 March 2008, Published online 8 September 2008 in Wiley Interscience (www.interscience.wiley.com) DOI 10.1002/bio.1054 Copyright © 2008 John Wiley & Sons, Ltd. Luminescence 2009; 24: 2–9 2 John Wiley & Sons, Ltd. Chemiluminescence determination of chlorpheniramine using tris(1,10- phenanthroline)–ruthenium(II) peroxydisulphate system and sequential injection analysis Fakhr Eldin O. Suliman*, Mohammed M. Al-Hinai, Salma M. Z. Al-Kindy and Salama B. Salama ABSTRACT: A sequential injection (SI) method was developed for the determination of chlorpheniramine (CPA), based on the reaction of this drug with tris(1,10-phenanthroline)–ruthenium(II) [Ru(phen) 3 2+ ] and peroxydisulphate (S 2 O 8 2– ) in the presence of light. The instrumental set-up utilized a syringe pump and a multiposition valve to aspirate the reagents [Ru(phen) 3 2+ and S 2 O 8 2– ] and a peristaltic pump to propel the sample. The experimental conditions affecting the chemiluminescence reaction were systematically optimized, using the univariate approach. Under the optimum conditions linear calibration curves of 0.1–10 mg/ml were obtained. The detection limit was 0.04 mg/ml and the relative standard deviation (RSD) was always < 5%. The procedure was applied to the analysis of CPA in pharmaceutical products and was found to be free from interferences from concomitants usually present in these preparations. Copyright © 2008 John Wiley & Sons, Ltd. Keywords: chemiluminescence; tris(1,10-phenanthroline)–ruthenium(II); peroxydisulphate; chlorpheniramine Introduction A large number of reports on the determination of various ana- lytes have appeared in the literature where chemiluminescence (CL) is coupled to techniques such as flow-injection analysis (FIA), high-pressure liquid chromatography (HPLC) and capillary electrophoresis (CE) (1–5). The marriage of these techniques to CL detection has enabled the emergence of low detection limits and wider dynamic ranges while using a very simple instrumental set-up. The major disadvantage of this arrangement is the high consumption of reagents as a result of using high flow rates. Ruthenium(II) complexes, such as tris(2,2′-bipyridyl)–ruthenium(II) [Ru(bpy) 3 2+ ] and tris(1,10-phenanthroline)–ruthenium(II) [Ru(phen) 3 2+ ] are among the most frequently utilized reagents for the generation of CL (6–15). The most acceptable mechanism by which Ru(phen) 3 2+ CL is obtained is via oxidation of Ru(phen) 3 2+ to the active Ru(phen) 3 3+ , either chemically or electrochemically. The emission of the ruthenium complex may arise from the energetic electron transfer reaction between Ru(phen) 3 3+ and a reducing agent. Ru(phen) 3 2+ is commercially available but it can be synthesized easily from ruthenium chloride and the common laboratory reagent 1,10-phenanthroline (16). Most ruthenium(II) complexes are expensive reagents. Ru(phen) 3 2+ and Ru(bpy) 3 2+ are the most often used ruthenium(II) complexes in CL reactions and both can be obtained at relatively lower cost. Both reagents are known to produce strong CL using a portfolio of oxidants and in the presence of many analytes. However, Ru(phen) 3 2+ is utilized to a much lesser extent than Ru(bpy) 3 2+ as CL reagent in chemical analysis, despite the fact that in many applications it was found to be of an equivalent or higher CL efficiency compared to Ru(bpy) 3 2+ (14, 17–20). Methods for the assay of barbituric acid in synthetic samples, enoxacin and isoniazid were developed using Ru(phen) 3 2+ and very low detection limits were obtained (18, 19, 21). This reagent was also used for the determination of glutathione and cysteine, using Ce(IV) as an oxidant (20, 22). One of the early reports on the use of Ru(phen) 3 2+ was on the analysis of oxalic acid in food samples using HPLC (23, 24). The electrochemiluminescent (ECL) generation of Ru(III) com- plexes is receiving a lot of interest due to the favourable charac- teristics of these species, such as excellent chemical stability, high emission quantum yield and long lifetime of the excited state (15, 25–32). The major limitations of ECL are those associated with electrodes, such as fouling, and the need for reconditioning of the electrode surface to sustain a constant CL signal. In addition electrochemical cells provide an additional complexity to the detection system. On the other hand, chemical generation of Ru(III) complexes avoids such complexity but is characterized by the instability of the reagents produced with respect to reduction. To overcome such an obstacle, Ru(phen) 3 2+ can be mixed with * Correspondence to: F. E. O. Suliman, Department of Chemistry, College of Science, Sultan Qaboos University, Box 36, Al-Khod 123, Sultanate of Oman. E-mail: fsuliman@squ.edu.om Department of Chemistry, College of Science, Sultan Qaboos University, Box 36, Al-Khod 123, Sultanate of Oman