Electrochemiluminescent Metallopolymer Coatings:  Combined Light and Current Detection in Flow Injection Analysis

The application of thin films of the metallopolymer [Ru(bpy)2PVP10]2+ for the electrochemiluminescent (ECL) detection of oxalate in a flow injection analysis system is reported, where bpy is 2,2‘-bipyridyl and PVP is poly(4-vinylpyridine). Immobilization of the ECL reagent means that it can be regenerated in situ, eliminating the need to constantly deliver it to the reaction zone. Electrochemically generated Ru3+ reacts with the analyte to form the excited-state [Ru2+]*, which luminesces at 610 nm. The reaction is optimal at low pH, where the layer is swollen and homogeneous charge transport through the layer is more facile. Unlike traditional approaches, we simultaneously monitor both the amperometric and luminescent response of the modified electrode. The precision of both signals is similar at ∼2% (n = 10). However, the ECL response has a larger dynamic range extending from the low-micromolar to higmillimolar range and a lower limit of detection, ∼0.2 μM or 4 pmol of oxalate injected. The ECL approach displays excellent selectivity for oxalate over a wide range of potential interferences including oxygen, amines, iron sulfate, ammonium nitrate, urea, and glucose. Ascorbic acid represents the most significant ECL interference. However, the signal observed for a 1 mM solution of ascorbic acid is still only 2.6% of the response observed for the injection of a similar concentration of oxalate.