Novel Electrodes For Voltammetric Determination Of Total Dissolved Iron In Coastal Waters

The coastal waters include river/water ditches,offshore area,reservoirs,salina,lakes/pond and so on.They are important for the coastal zone area.Iron is one of the essential micronutrients for organisms in ecological system.Iron plays an important factor in plant metabolism and chlorophyll synthesis.Besides,it is believed to be a limiting factor for primary productivity in marine ecosystems.Thus,accurate analysis of iron in coastal waters has great significance in studying coastal biogeochemistry cycle and realizing coastal environment monitoring.Many techniques have been developed to determine iron.However,most of these methods need expensive and bulky devices which restrict their use for in situ determination.Moreover,some methods suffer from serious matrix interferences.Electrochemical stripping voltammetry has been widely regarded as a sensitive technique for iron determination due to its simple equipment,low detection limit,fast and accurate detection,easy automation and suitable for in situ determination.Therefore,electrochemical method take an increasing significant role in trace iron determination.The choice of working electrode is the key problem in electrochemical methods.The mostly used working electrode is mercury electrode,however,it has some drawbacks including toxicity and difficulties in the handling.In this thesis,novel electrodes were proposed in view of the problem of iron determination.The established methods have been successfully applied to the determination of total dissolved iron in coastal river waters and coastal sea waters.The main contents are as follows:1.An electrochemical sensor based on reduced graphene oxide(rGO)and gold nanoparticles(AuNPs)modified electrode via one single step was developed for determination of total dissolved iron in coastal waters.2-(5-bromo-2-pyridylazo)-5-diethylaminophenol(5-Br-PADAP)was used as complexing agent of iron,5-BrPADAP can be complexed with iron in acidic buffer solution.rGO was acted as a support provided large specific surface area for AuNPs,which would facilitate the electrochemical reduction of Fe(III)-5-Br-PADAP.Under the optimized conditions,the responses of Fe(III)at this established sensor were linear in the range of 0.03~3 ?mol/L with a detection limit of 3.5 nmol/L.The fabricated sensor also had excellent reproducibility and repeatability,it has been successfully applied to the determination of total dissolved iron in real coastal waters.2.The reduced graphene oxide(rGO)and gold film(AuF)modified electrode via two steps was used for the determination of total dissolved iron in coastal sea waters.Sea water is slightly alkaline,the pH is about 8.In order to accurately determine total dissolved iron in coastal sea waters,2,3-dihydroxynaphthalene(DHN)was used as complexing agent of iron,the complexing agent applied to reacting with iron in alkaline buffer solution,potassium bromate was used as a catalyst.Under the optimized conditions,the liner range of the electrode is segmented(0.01~0.1 ?mol/L and 0.1~1 ?mol/L).The results of this method are in agreement with the polarography,it has been successfully applied to determine total dissolved iron in coastal sea waters.3.The concentration and distribution of total dissolved iron in typical coastal river waters.Gold electrode was used as working electrode.5-Br-PADAP was used as complexing agent of iron with a short chelating reaction time((27)3 min),while gold electrode has a good response to this complex.Under the optimized conditions,the response of Fe(III)at the electrode was linear in the range of 0.01 ?mol/L to 1 ?mol/L with a detection limit of 1.2 nmol/L.The results of this method were in agreement with the spectrophotometry.Besides,this method has been successfully applied to determine total dissolved iron in Dagujia river of Yantai,China(twelve sampling stations in dry season and wet season).The relationship between the concentrations of total dissolved iron with dissolved oxygen and salinity were also discussed.Experiments showed that the gold electrode combined with adsorptive stripping voltammetry can be adopted for determination of total dissolved iron in coastal river waters.