Flow injection analysis of tetracyclines using inhibited Ru(bpy)3(2+)/tripropylamine electrochemiluminescence system

Tetracyclines (TCs) were found to strongly inhibit the electrochemiluminescence (ECL) from the Ru(bpy)3(2+)-tripropylamine system when a working Pt electrode was maintained at 1.05 V (vs. Ag/AgCl) in pH 8.0 carbonate buffer solution. On this basis, a flow injection (FI) procedure with inhibited electrochemiluminescence detection has been developed for the determination of tetracycline (TC) and oxytetracycline (OTC). Under the optimized condition, the linear ranges of 2.0 x 10(-8)-1.0 x 10(-5) and 1.0 x 10(-8)-1.0 x 10(-5) g/mL and the detection limits of 4.0 x 10(-9) and 3.8 x 10(-9) g/mL were obtained for TC and OTC, respectively. The relative standard deviations (RSD) were 0.68% and 1.18% for 5.0 x 10(-7) g/mL TC and OTC (n = 13), respectively. The method showed higher sensitivity than most of the reported methods. It was successfully applied to the determination of tetracycline in a Chinese proprietary medicine, Tetracyclini and Cortisone Eye Ointment, and the residues of tetracycline in honey products. The inhibition mechanism has been proposed due to an energy transfer between electrogenerated Ru(bpy)3(2+)* and benzoquinone derivatives at the electrode surface.