Electrochemical Determination Of Nitrite Using Modified Polyaniline-Covered Glassy Carbon Electrode

Nitrite is one of the pollutants widely found in natural waters, and the determination of nitrite has been a hot topic of research for a long time. In this paper, on the one hand the noble metal particles (Ag and Pd) were electrochemically deposited onto polyaniline (PANI) to prepare Ag/PANI modified glassy carbon electrode (Ag/PANI/GCE) and Pd/PANI modified glassy carbon electrode (Pd/PANI/GCE); on the other hand copolymer of aniline and o-aminophenol (PAOA) was electrochemical polymerized to prepare PAOA modified glassy carbon electrode (PAOA/GCE). The three kinds of electrodes were employed for the determination of nitrite. An analysis electrochemical system has been developed, characterized, and optimized for the determination of nitrite. Also, the selectivity, sensitivity, detection limits, and stability of the three electrodes were evaluated.The deposition of metal (Ag and Pd) coating on PANI substrate was achieved by cyclic voltammetry (CV) method, and the optimal conditions for the preparation was found to be CV scan for 1000 s with the AgNO3 concentration of 1.5 mmol L-1 and PdCl2 concentration of 0.5 mmol L-1, respectively. X-ray Photoelectron Spectroscopy (XPS) spectra indicated the formation of metallic Ag and Pd on Ag/PANI/GCE and Pd/PANI/GCE, respectively. SEM images of the two kinds of electrodes showed that metal Ag and Pd existed as microparticles consisted of number of nanoparticles. Ag nanoparticles had a smaller diameter of about 100 nm, while Pd nanoparticles were more easily aggregated.The Ag/PANI/GCE and Pd/PANI/GCE were employed for the determination of nitrite in water. Under the same conditions, the two electrodes exhibit enhanced electrocatalytic behavior to the oxidation of nitrite compared to the PANI modified GCE. The peak potential for nitrite oxidation was 1.2 V for PANI/GCE,1.0 V for Ag/PANI/GCE and 1.03 V for Pd/PANI/GCE, respectively. The solution pH had obvious influence on the determination of nitrite and the optimal condition was found at pH 2. As pH increased from 2 to 4, the response current decreased because of the decade of the electrochemical activity of PANI. Temperature had an apparent impact on the detection, and the response current increases with increasing temperature.It was also found that Ag/PANI/GCE and Pd/PANI/GCE has relatively high sensitivity (65.1μA (mmol L-1 cm2)-1 for Ag/PANI/GCE and 116.1μA (mmol L-1 cm2)-1 for Pd/PANI/GCE) with excellent stability and selectivity. Results showed that K+, Na+, NH4+, Mg2+, Zn2+, Cu2+, Mn2+, Cl-, SO42-, NO3-, citric acid and glucose has no obvious impact on the detection of nitrite.Considering that the Ag/PANI/GCE and Pd/PANI/GCE performed well only at acidic pH, which would limit its application in drinking water, copolymerization of aniline and o-aminophenol was employed to prepare PAOA/GCE for the determination of nitrite. Results showed that pH had no significant effect on the redox activity of PAOA as solution pH increased from 2 to 8. Temperature has an apparent impact on the detection, and the response current increases with increasing temperature. It was also found that PAOA/GCE has relatively high sensitivity (64.3 μA (mmol L-1 cm2)-1) with excellent stability and selectivity. Results showed that K+, Na+, NH4+, Mg2+, Zn2+, Cu2+, Mn2+, Cl-, SO42-, NO3-, citric acid and glucose has no obvious impact on the detection of nitrite. In addition, the peak potential for nitrite oxidation was 0.93 V for PAOA/GCE, which is lower than that of Ag/PANI/GCE and Pd/PANI/GCE.In conclusion, these PANI-based electrodes can be easily prepared, which provides a quick and simple method for nitrite detection. Meanwhile, the electrodes exhibit relatively high sensitivity with excellent stability and selectivity, which could be a good candidate as an electrochemical sensor in the determination of nitrite.