Analytical Sciences

Application of a New Iridium Complex as a Chemiluminescence Reagent for the Determination of Tryptophan

Fanghui WU, Bihai TONG, and Qianfeng ZHANG

School of Chemistry and Chemical Engineering, Institution of Molecular Engineering and Applied Chemistry, Anhui University of Technology, Maanshan 243002, P. R. China

It was found that a novel iridium complex, [(dpci)₂Ir(bvbbi)](PF₆) (dpci = 3,4-diphenylcinnoline, bvbbi = N,N′-bivinyester-¹H,¹′H-[2,2′] bibenzimidazole), with Ce(IV) in the presence of sodium sulfite can induce a great chemiluminescence (CL) emission. More importantly, a rapid and sensitive CL method for the determination of tryptophan coupled with a flow-injection analysis (FIA) technique has been developed based on the inhibition effect of the tryptophan to the CL emission of [(dpci)₂Ir(bvbbi)](PF₆)-Ce(IV)-SO₃²⁻ system. Under the optimum conditions, the decreased CL intensity is proportional with the concentration of tryptophan in the range of 5.0 × 10⁻⁷ to 2.0 × 10⁻⁵ mol L⁻¹, and the detection limit is 8.2 × 10⁻⁸ mol L⁻¹ (3σ). The relative standard deviation (RSD) for 11 parallel measurements of 1.0 × 10⁻⁵ mol L⁻¹ tryptophan is 2.7%. The proposed method has been applied successfully for the determination of tryptophan in its pharmaceutical formulations. Moreover, the possible inhibition mechanism of tryptophan on [(dpci)₂Ir(bvbbi)](PF₆)-Ce(IV)-SO₃²⁻ CL system was briefly discussed.

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