Determination of amlodipine using terbium-sensitized luminescence in the presence of europium(III) as a co-luminescence reagent

A sensitive time-resolved luminescence method for the determination of amlodipine (AM) in methanol and in aqueous solution is described. The method is based on the luminescence sensitization of terbium (Tb³⁺) by formation of a ternary complex with AM in the presence of tri-n-octylphosphine oxide (TOPO) as co-ligand, dodecylbenzenesulfate as surfactant and europium ion as a co-luminescence reagent. The signal for Tb-AM-TOPO is monitored at λ_ex = 242 nm and λ_em = 550 nm. Optimum conditions for the formation of the complex in aqueous system were 0.015 M Tris (hydroxylmethyl) amino methane buffer, pH 9.0, TOPO (1.0 × 10^-4 M), Eu³⁺ (2.0 × 10^-7 M), dodecylbenzenesulfate (0.14%) and 6.0 × 10^-5 M of Tb³⁺, which allows the determination of 10-50 ppb of AM with a limit of detection of 1.2 ppb. The relative standard deviations of the method range between 0.1 and 0.2% indicated excellent reproducibility of the method. The proposed method was successfully applied for the assay of AM in pharmaceutical formulations and in plasma samples. Average recoveries of 98.5 ± 0.2% and 95.2 ± 0.2% were obtained for AM in tablet and plasma samples respectively.