Study On Construction Of Electrochemiluminescence System And The Rapid Detection Of Melamine By Flow Injection Method

Electrogenerated chemiluminescence （ECL） is a technique combined electrochemistry withchemiluminescence has lots of advantages, such as high sensitivity, broad linearity, reactioncontrollable, simple equipment, rapid analysis and easy to automate. ECL technology waswidely used in biology, medicine, pharmacy, clinical, food, environment and other fields.With the development of electrochemiluminescence analysis techniques, building newelectrochemiluminescence system is of great significance to further improve detectionsensitivity and to broaden its scope of application. The flow injection electrochemilumin-escence is a analytical procedure combined flow injection technique and electrochemicalu-minescence detection technology. The new method has some unique advantages. It not onlyimproved the analysis speed and selectivity and sensitivity of analytical methods, but also wasparticularly suitable for automated analysis. The technology on detection of melamine usingflow injection electrochemiluminescence overcomed defects as expensive instrument,time-consuming, complicated processesing exist in conventional detection methods, haspractical importance in food safety testing.The detection performance of the flow injection electrochemiluminescence system wasstudied by Ru（bpy）₃²⁺/TPrA. The chemiluminescence reaction conditions and instrumentdetection parameters were optimized. The optimal conditions were selected, detectionpotential at1.25V, sample injection of100μL at90μL/s, TPrA concentration at0.1mol/L,0.1mol/L of phosphate buffer （pH8.5）, running buffer of0.01mol/L（pH8.5）. The ECLintensity was linear with the concentrations of Ru（bpy）₃²⁺in the range of5.0×10^-9～1.0×10^-7mol/L, with a detection limit（S/N=6） of1.0×10^-9mol/L. The relative standarddeviation （RSD） of peak height was3.2%. The results showed that flow injectionelectrochemiluminescence had high sensitivity, wide linear range, rapid analysis and lesssample consumption.Two electrochemiluminescence systems were built by adding nonionic surfactant Tween20to Ru（bpy）₃²⁺/TPrA and using DBAE as co-reactant instead of TPrA. The results showed thatafter adding Tween20, the ECL intensity was linear with the concentrations of Ru（bpy）₃²⁺intherange of5.0×10^-11～5.0×10^-7mol/L, with a detection limit of1.0×10^-11mol/L, which indicated that Tween20has sensitivity effect on ECL. Preliminary studies on sensitizingmechanism showed that Tween20can promote the direct oxidation of TPrA on electrodesurface and increases the oxidation current, and the best light-emitting potential ofRu（bpy）₃²⁺/TPrA system was slightly increased after adding Tween20. The reaction and testconditions of Ru（bpy）₃²⁺/DBAE system were optimized. Electrode potential of1.45V, DBAEconcentration of50mmol/L, and pH of7.5, sample push velocity of70μL/s were selected.Under optimal conditions, the detection sensitivity of Ru（bpy）₃²⁺was5.0×10^-10mol/L, andthe linear range was1.0×10^-9～5.0×10^-7mol/L. The results showed that, Ru（bpy）₃²⁺/DBAEsystem has a higher sensitivity and wider linear range compared with Ru（bpy）₃²⁺/TPrAsystem.A new flow injection electrochemiluminescence analytical method of melamine has beenproposed based on its sensitizing effect on the ECL of Ru（bpy）₃²⁺. The experimentsinvestigated the effect of detection potential and medium pH on the Ru（bpy）₃²⁺ECL, and theeffect of Ru（bpy）₃²⁺concentration on the detection results of melamine. Under optimumconditions, the relationship between the increased values of ECL intensity after addingmelamine and its concentration was established. The recovery rate of melamine in milkpowder and liquid milk was tested by this method. It was found that when potential at1.0V,medium pH was9.5, the maximum ECL intensity of Ru（bpy）₃²⁺was obtained. Under theseconditions, the Ru（bpy）₃²⁺concentration of2.5×10^-4mol/L was selected for the melaminedetection. The increased values of ECL intensity after adding melamine was linear with theconcentration logarithm of melamine in the range of1.0×10^-8～1.0×10^-3g/L, with adetection limit of5.0×10^-9g/L. The recovery rate of this method for melamine in sampleswas85%～110%. The results of melamine detection in milk powder, liquid milk of theproposed method were basically similar to the data with HPLC. It shows that the method canbe used for the rapid detection of melamine in dairy products.