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

Abstract

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) 3 3+) 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 μL, 0.5 mM Ru(bipy) 3 2+ 30 μL, 0.4 M Na acetate 16 μL and I sample 15 μL; the flow rates were 60 μL s −1 for the aspiration into the holding coil and 100 μL 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 μM I ( r = 0.9997; n = 9) with rectilinear section in the range 0.1–10 μM I ( r = 0.9995; n = 5). The limit of detection (3 σ) was 0.05 μM I. Repeatability of peak heights (R.S.D., n = 10) ranged between 2.4% (0.5 μM I) and 2.0% (7 μM 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.