Development Of An All-solid-state Sufate Ion-selective Electrode And Its Application In Seawater

Dissolved sulfate(SO42-)is one of the most abundant anion in modern seawater and accounting for more than 99%of the total sulfur.The sulfate concentration of the ocean could track the oxidation history of the Earth's surface.In addition,the sulfate concentration may affect several important biological processes,such as carbonate mineralogy,microbial mediated organic matter remineralization,sedimentary phosphorous regeneration,nitrogen fixation and so on,resulted the change of the global carbon cycle,climate and marine productivity variation.Sulfate is a major component of the pore water,and it is viewed as a feasible method to investigate the underwater gas hydrate by using the abnormal changes of sulfate concentration in sediment pore water.SO42-in seawater could aggravate the corrosion of steel and concrete material,destroying the marine engineering facilities such as bridge,dam and wharf.Therefore,developing a novel high-precision sulfate sensor to measure the sulfate precisely and rapidly in ocean is urgently needed for the exploitation of the marine resources and protection of marine engineering facilities.In this paper,the basic principle and performance evaluations of ion-selective electrodes,and the advantages of all-solid-state electrodes compared to conventional electrodes were discussed respectively.In addition,the application prospect of doped conductive polymer in electrochemical sensor was described too.In the experimental section,the electrodes with aniline and barium sulfate which served as the active material of sensitive membrane,and electrodeposited gold wire as substrate were fabricated firstly.The all-solid-state sulfate ion-selective electrodes were prepared by chronoamperometry method at ambient temperature.Then,the detection range and repeatability of the electrodes were studied.Performances of the electrodes were improved by aniline hydrochloride served as the active material of sensitive membrane with cleaned gold wire as substrate,which were suitable for rapid seawater detection.The improved electrodes were studied in in many respects,such as the preparation of the sensitive membrane coated,generation of response potential signal,transportation of charge between electrode and solution.The electrodes improved had the advantages of simple operation,cheap raw materials,short response time and easy to carry.The electrodes exhibited excellent nernstian linear response to sulfate in the concentration range of 1.0×10-4 to 1.0 mol/L Na2SO4 solutions made by freshly prepared 3.5%NaCl solution,with a slope of-26.62 mv/decade(R2>0.99).The potentiometric response of the electrode was independent of pH in the range of 5.5-8.5 and performed superior repeatability,which could be applied to the pH environment of seawater.The electrodes behaved good selectivity to several anions,such as Cl-?Br-?I-?NO3-and so on The polyaniline has biological toxicity,however,which may prevent the fouling organisms adhesion on the surface of the electrode in real-time seawater,thus improved the reliability of electrode.In the meantime,the electrodes were convenient to assembly and integrated with other chemical electrode,which could be served as multi-parameter chemical sensor to capture data.The electrodes improved could be used to rapid laboratory analysis and self-contained/on-line in-situ monitoring in real-time,distant and inaccessible site,such as the ocean.The deficiency of sulfate ion-selective electrode in marine application was filled.