Evaluation of electrogenerated chemiluminescence from a neutral Ir(III) complex for quantitative analysis in flowing streams

Though recently Ir(III) complexes have attracted much interest in electrochemiluminescent (ECL) analysis due to their high emission in various wavelengths, there were a few studies reported on its analytical applications. In this study, we evaluate the ECL from (pq)₂Ir(acac) (pq = 2-phenylquinolate, acac = acetylacetonate) for the use in flow injection analysis. An aqueous solution of the analyte and (pq)₂Ir(acac) passes through the reaction/observation cell, and then ECL reaction is generated by electrochemical initiation on the analyte and (pq)₂Ir(acac). Tri-n-propylamine (TPrA) is used as a representative analyte for evaluation. Additionally, a comparison is made of the relative ECL intensities obtained for a variety of analytes including oxalate, amino acids, aliphatic amines, and NADH. The (pq)₂Ir(acac) produces efficient ECL upon TPrA exhibiting the limit of detection of 5 nM with a linear range of 3 orders of magnitude in concentration whereas 20 nM is observed in the conventional Ru(bpy) ₃²⁺ system. It shows particular sensitivity advantages for oxalate, proline, and tartaric acid. The ECL generation upon various analytes proposes direct applicability of (pq)₂Ir(acac) as a post-column detection tool.