Construction of Poly(methylene blue) on Carbon Nanotubes Ionic Liquid Paste Electrode for Sensitive Detection of Nitrite

An amperometric sensor for determination of nitrite was fabricated by electropolymerizing methylene blue (MB) on carbon nanotubes ionic liquid paste electrode (PMB/MWCNTs-CILE). The presence of MWCNTs in the carbon ionic liquid electrode could enhance the surface coverage amount of PMB and decrease the degradation of PMB, and promote the electron transfer rate. The proposed sensor showed electrocatalytic activity for the oxidation of nitrite in 0.1 M phosphate buffer solution (pH 4.0) and the oxidation peak occurred at low overpotential (0.768 V vs. Ag/AgCl). The effects of pH of the electrolyte, amount of MWCNTs, electropolymerization cycles and applied potential on the sensitivity of the sensor have been systemically investigated. The catalytic peak current was found to be linear with the nitrite concentration in the range of 0.5-67.9 mu M, with a correlation coefficient of 0.9997, using amperometric measurements. The detection limit of 0.25 mu M was obtained, with a sensitivity of 2.53 mu A mu M-1 cm(-2). The sensor showed a fast response to nitrite (less than 5 s). The relative standard deviation (RSD) of the sensor response to 50 mu M NaNO2 was 1.8% for eight replicate measurements and the sensor retained 94% of its initial response after it was kept in air for one month, indicated the sensor had good reproducibility and stability.