Study On Hydroxyapatite-Based Eletrochemical Senesor For Analysis Of Lead, Cadmium, Copper

As an important factor of monitoring the food pollution, the content of heavy metals in food required accurate measurement which was also of significance in food safety analysis. The economy, simple and environmentally friendly new method for the rapid on-site detection will become the focus of the research, because it not only can achieve a high proportion of separation between qualified and unqualified, but also became more beneficial to the real situation reflection and real-time supervision.Electrochemical instruments of low cost and easy operation meet the demands of different food inspection departments, and that’s the major reason electric analytical chemistry can be widely used. Square wave stripping voltammetry had higher sensitivity than some other electrochemical methods and applied to multielement synchronously fast determination. This study was based on hydroxyapatite dispersed in SDBS with [BMIM]PF6which effectively made up for the shortage of conductivity and viscosity of hydroxyapatite. The mixture was dropped on screen-printed carbon electrode and followed by Nafion at the top to enhance the stability of SPCE. The SEM, CV and EIS characterized the modified SPCE, and the electrochemical stripping responses of lead, cadmium and copper on which were carried out. In this new technique of electrochemical sensor, tea and mushroom were detected by SWV after pretreating the food samples by microwave digestion.This thesis mainly consists of six aspects as follows:The first part summarized the hazards of heavy metals and the status of food contamination, made a comparison between conventional detection methods of heavy metals and electrochemical method. Also, each study was introduced.The second part used the theory that hydroxyapatite can effectively improve the response of electrochemical sensor for metal. In this report, hydroxyapatite/SDBS was applied to modify the screen-printed carbon electrode, which was becoming much more stable by adding Nafion. The new method was easy operating and allowed lead preconcentration at the electrode surface. The analysis of the selected heavy metals was performed by square-wave stripping voltammetry (SWV). The experimental affecting factors were optimized as follows,0.1mol/L pH4.5sodium acetate buffers was employed as the supporting electrolyte, amount of hydroxyapatite was2mg/mL, the concentration of I was0.010mol/L, and accumulation time was270s. Under the optimized working conditions, a linear response range from2 μg/L to300μg/L was obtained, y(μA)=0.0434x(μg/L)+0.0265(R=0.992). The detection limit for lead determination was0.460μg/L(S/N)=3. The sensor presented good repeatability, evaluated in terms of relative standard deviation (R.S.D.=4.59%) for n=5, which indicated that the method can be used to lead determination in tea.The third part established a novel electrochemical sensor for rapid determination of trace lead. The screen-printed carbon electrode wad modified by hydroxyapatite, ionic liquid and SDBS. The influence of variables, like the proportion of hydroxyapatite to ionic liquid, the modification, et al. were optimized in sodium acetate buffer (0.1mol/L) by square-wave stripping voltammetry. ICP-MS was used to verify this method determining the lead in tea samples. The optimum determination conditions were as follows:0.1mol/L pH5.0sodium acetate buffers were employed as the supporting electrolyte, amount of hydroxyapatite was2.0mg/mL, and accumulation time was210s. Under the optimized working conditions, a linear response range from4μg/L to250μg/L was obtained, y(μA)=0.0278x(μg/L)+0.0186(R=0.998), the detection limit for lead determination was0.386μg/L (S/N)=3. The sensor was evaluated in terms of relative standard deviation (R.S.D.=3.87%) for n=5. This electrochemical sensor for rapid detection of lead effectively improved the sensitivity, stability and security. In addition, it’s accurate, inexpensive and truly reflects the contents of lead in tea.The forth part was based on the system built up in third part. The conditions were optimized by SWV. ICP-MS was used to verify this method determining the cadmium in mushroom samples. The optimum determination conditions were as follows:0.1mol/L pH5.0sodium acetate buffers were employed as the supporting electrolyte, amount of hydroxyapatite was2.5mg/mL, and accumulation time was240s. Under the optimized working conditions, a linear response range from5μg/L to100μg/L was obtained, y(μA)=0.0304x(μg/L)+0.0218(R=0.992), the detection limit for lead determination was0.780μg/L (S/N)=3. The sensor was evaluated in terms of relative standard deviation (R.S.D.=5.05%) for n=5. This electrochemical sensor for rapid detection of cadmium effectively improved the sensitivity, stability and security. In addition, it’s accurate, inexpensive and required easy operation. The electrochemical sensor possessed significant innovation and a wide range of application potential.The fifth part was to optimize the conditions of simultaneous determination of lead(Ⅱ) and copper(Ⅱ)by the detection technique that established in part three. The optimum determination conditions were as follows:the supporting electrolyte was0.1mol/L pH5.5sodium acetate buffers, amount of hydroxyapatite was2.5mg/mL, deposition potential was-1.1V, and accumulation time was240s.The last part made a summary of the thesis, and meanwhile looking forward to the futurity of this field.