Prepartion And Application Of The Ammonia, Nitrite Electrodes

In this study，embedding and heat sealing technology were used to prepareelectrodes, that is the tip of the metal disc was coated with the galss insulating layer andthe adhesion portion of the electrode and the glass tube by heating method toaccomplish, the exposed tip surface of the wire disc is the electrode surface area. So thetip diameter of Pt microelectrode and Pt electrode respectively were70um and0.1mmin this study. Microelectrode and conventional electrode had advantages anddisadvantages:1) the characteristic of the microelectrode is higher accuracy andsensitivity than the conventional electrode,2) microelectode can measure the physicaland chemical parameres of micro-environment without disturbance and can not destroythe point of micro-ecological environment which was measured,3) the physical strengthand stability of the conventional electrode are higher than microelectrode and theproduction ways of the conventional is more simple. By electrochemicalcharacterization and anti-jamming ability detection, indicating that the microelectrodeand conventional electrode have good stability and electrochemical activity, theseelectodes can be used for electrochemical analysis and electrochemical modificationwhich is to extend functionality of these.Electrochemical modification way is to impart specific properties of the functionalgroup to the surface of the electrode, and to improve the reaction speed, selectivity andsensitivity of the electrode. In this study, chronoamperometry was used at-0.31V （V vsAg/AgCl） for100s in a solution of0.04M chloroplatinic acid for the electrodepositionof Pt nanoparticles onto the surface of the pretreated Pt disc. The scanning electronmicroscopy （SEM） was employed to respectively observe the surface morphology ofthese nPt/Pt electrodes which were electrochemically deposited for different time,research the effect that the surface structure of the electrode to its electrochemicalactivity: it is that many Pt nanoparticles evenly and tidily deposited on the Pt surfacecould improve the electrocatalytic activity of the modified electrode, electrodepositiontime was100seconds, and nanostructures couldn’t be formed on the Pt surface whenthe deposition time was too short or too long. Cyclic voltammetry was employed toevaluate the electrochemical behavior of the modified electrode, found that nPt/Ptmicroelectrode and nPt/Pt electrode respectively have a good linear resoponse ofammonia and nitrite, so these electrodes can be used for quantitative analysis. Ammonia and nitite can lead to water eutrophication when concentration is toohigh and is a great threat to human health. Recently, the determination of ammonia andnitrite concentration in water has been widely recognized, and much attention is paid onthe method to determine it fast and accurately. Since the electrochemical method doesnot require the pretreatment of sample, which can quickly, accurately and easilydetermine the concentration in solutions, so in this study, nPt/Pt microelectrode wasused to measure the amnion concentiation and nPt/Pt electrode was used to measure thenitrite concentration.nPt/Pt microelectrode was used to measure the （NH₄）₂SO₂solutions which weresame concentration and different pH. No peak current could be found for alkalinesolution in the cyclic voltammetry curve, while under acidic conditions, the smaller pHvalue, the greater peak current will be. It means NH4+was electrochemical oxidated bynPt/Pt microelectrode. So it is must to make the pH of solution be same when measurethese concentration, in this study, ammonia concentration was measured in the solutionpH=3.Cyclic voltammetry was respectively employed in six （NH₄）₂SO₂solutions todetermine the ammonia concentrations, and pertinence curve between ammonia oxidepeak currents and ammonia concentrations was found. The correlation coefficient of theregression curve was0.998, that means the nPt/Pt microelectrode could quantitativelydetermine the ammonia concentrations and could not interfere by ions.After repeatedexperiments, the detection limits of the ammonia sensor was4.5×10^-4M.The way of measuring nitrite concentration by nPt/Pt electrode was same as theammonia measruring. Cyclic voltammetry was respectively employed in six NaNO2solutions to determine the nitrite concentrations, and pertinence curve between nitritereductive peak currents and nitrite concentrations was found. The correlation coefficientof the regression curve was0.996, that means the nPt/Pt electrode could quantitativelydetermine the nitrite concentrations and could not interfere by ions.After repeatedexperiments, the detection limits of the nitrite sensor was0.3×10^-4M. The nPt/Ptelectrode was used to measure the nitrite concentration in outlet water of UASB and theN-（1-naphthyl）-ethylenediamine spectrophotometry was used to measure the samenitrite concentration for contradistinction. The differences of two nitrite concentrationmeasured by the two different ways was less than6%.