Sequential injection analysis (SIA)-chemiluminescence determination of indomethacin using tris[(2,2′-bipyridyl)]ruthenium(III) as reagent and its application to semisolid pharmaceutical dosage forms

Automated sequential injection (SIA) method for chemiluminescence (CL) determination of nonsteroidal anti-inflammatory drug indomethacin (I) was devised. The CL radiation was emitted in the reaction of I (dissolved in aqueous 50% v/v ethanol) with intermediate reagent tris(2,2'-bipyridyl)ruthenium (III) (Ru(bipy)331) in the presence of acetate. The Ru(bipy)3 (3). was generated on-line in the SIA system by the oxidation of 0.5 mM tris(2,2'-bipyridyl)ruthenium(II) (Ru(bipy)3 (2+)) with Ce(IV) ammonium sulphate in diluted sulphuric acid. The optimum sequence, concentrations, and aspirated volumes of reactant zones were: 15 mM Ce(IV) in 50 mM sulphuric acid 41 mu L, b.5 mM Ru(bipy)(3)(2+) 30 mu L, 0.4 M Na acetate 16 mu L and I sample 15 mu L; the flow rates were 60 mu L s(-1) for the aspiration into the holding coil and 100 mu L s-1 for detection. Calibration curve relating the intensity of CL (peak height of the transient CL signal) to concentration of I was curvilinear (second order polynomial) for 0.1-50 mu M I (T = 0.9997; n = 9) with rectilinear section in the range 0.1-10 mu M I (T = 0.9995; n = 5). The limit of detection (3 sigma) was 0.05 mu M 1. Repeatability of peak heights (R.S.D., n = 10) ranged between 2.4% (0.5 [mu M 1) and 2.0% (7 [mu M I). Sample throughput was 180 h(-1). The method was applied to determination of 1 to 5% of I in semisolid dosage forms (gels and ointments). The results compared well with those of UV spectrophotometric method. (C) 2007 Elsevier B.V. All rights reserved.