Factors affecting tris(2,2'-bipyridyl) ruthenium(II) (Ru(bpy) 3 2þ )/tertiary amine electrochemiluminescence (ECL) were investigated in the present work with several tertiary amines as coreactants. Some new phenomena different to those of traditional Ru(bpy) 3 2þ /tripropylamine were observed, such as the different responses of different coreactants to the hydrophobic nature of the working electrode and the ECL emission of triethanolamine at 0.85 V. The pK a value (acid dissociation constant) for the deprotonation of tertiary amine group in the coreactant molecules and solubility of coreactants affect the ECL profiles vs. electrolyte pH. Moreover, the solubility of coreactants is also related to the ECL response to the addition of surfactants and electrode hydrophobic nature. Investigation of the effects of molecular structures indicated that molecules restricting the formation of the trigonal planar structure of the active radical in the electrooxidation procedure resulted in low ECL emission. The behaviors of hydroxyl and carboxylic group as substituents of a-carbon are also totally different to the traditional opinions about the ECL from Ru(bpy) 3 2þ / tertiary amines.

Due to the highly sensitive electrochemiluminescence (ECL), tris(2,2′-bipyridyl) ruthenium(II) (Ru(bpy) 3 2+ )is often used in the field of bioarrays with the help of co-reactants. However, the generally used co-reactant, tripropylamine (TPA), is toxic, corrosive and volatile. Therefore, the search for safe, sensitive and economical co-reactants is critical. Herein, three aminocarboxylic acids, ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), and 2-hydroxyethylethylene diaminetriacetic acid (HEDTA), have been investigated as potential co-reactants for promoting Ru(bpy) 3 2+ ECL behaviour. A possible ECL mechanism is also presented. The experimental results suggested that the co-reactants have a different ECL behaviour compared to TPA, such as different pH-and surfactant-responses. The detection limits of Ru(bpy) 3 2+ using NTA, EDTA and HEDTA as co-reactants are 1, 60 and 680 fmol·L  1 , respectively. The results indicate that NTA has a much higher efficiency than TPA to excite Ru(bpy) 3 2+ ECL under their own optimal conditions. NTA could be widely used in many fields because it is less toxic, corrosive and volatile than TPA. Moreover, using Ru(bpy) 3 2+ ECL, a sensitive method for the detection of aminocarboxylic acids is also developed. An improvement of four orders of magnitude in detection limits is obtained for EDTA compared to the known Ru(bpy) 3 2+ chemiluminescent methods.Ru(bpy) 3 2+, electrochemiluminescence, co-reactants, aminocarboxylic acids

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