Research And Development On The Nitrate Ion Electrode

Nitrate is the most stable compound in various forms of nitrogen compounds. It is widelyexisted in natural environment, food, industrial products and ecological system. Many studieshave shown that excessive nitrate is not only harmful to the environment but also people’shealth badly. Therefore, to establish a simple, sensitive, accurate method for detecting traceamounts of nitrate is essential. Among many nitrate detection methods, the electrochemicalanalysis has attracted more attention. Compared with other methods, this method hasadvantages of simple and rapid analysis, low cost, high sensitivity. The modified electrodesand ion selective electrode of nitrate were developed, which were based on the Nernstprinciple and achieved satisfactory results. The main contents are listed as follows:(1)The modified electrode was developed based on nitrate-doped polypyrrole.Nitrate-doped polypyrrole films on a glassy carbon substrate had been preparedelectrochemically in acetonitrile and potassium nitrate in aqueous. The effects of pH andcoexiting ions were investigataed under the optimized reaction condition. The obtained resultindicated that the electrode showed a good linear range of10-1~10-4mol/L and a slope of-52±1.0mV/dec with a detectable concertration of3.16×10-5mol/L in the pH range of3.5~7.5.(2)The sensing material was synthesized and the response mechanism of metalcomplexes as the active material for nitrate was studied. The impact of the choice ofplasticizer and the composition ratio of the membrane were discussed. After the comparisonof experiments, the optimized membrane performance to nitrate was gotten with themembrane having I:PVC:TDAB:NPPE in the ratio3:32:1:64(w/w). The electrode had alinear response range of1×10-1~1×10-5mol/L to nitrate with a slope of-54±1.0mV/dec and adetection limit of3.7×106mol/L. Other interfering ions would not affect the performance ofthe electrode.(3)An all-solid-state nitrate ion-selective electrode with glassy carbon electrode as basalelectrode, polypyrrole as transducer layer, Poly(vinyl chloride)(PVC) as the basal membranewas reported. The results showed that the electrode exhibited a near Nernstian potential linearrange of1×10-5~1×10-1mol/L of nitrate concentration with a slope of-54±1.0mV/dec and alow detection limit of3.16×10-6mol/L. The electrode had short response time, stability andgood reproducibility, high mechanical strength, a lifetime of up to three months.(4)The improvement of all solid nitrate ion selective electrode mainly in the followingthree aspects: the conductive polyaniline was as intermediate; the PTFE tube was replaced byPVC sleeve; protective sleeve was added to electrodes in order to protect the electrode beforeand after measurements from other external forces. The improved electrode was better thanthe electrode made in the previous chapter, which was found through the study ofelectrochemical impedance spectroscopy of the electrode. The results showed that the slopewas-55±1.0mV/dec, closer to the theoretical value. There was also lower detection limit of2.7×10-6mol/L, more rapid response time, longer service life of the electrode.