Study Of The Rapid Detection Electrochemical Sensor Technology Of Lead And Other Heavy Metals In Tea

Tea was rich in tea polyphenols, amino acids, vitamins, alkaloids and various trace elements, which was recognized as natural health drinks and loved by the world peoples. However, the tea also contained heavy metals which were hazard to human health. The content of heavy metals have been closely watched by all around people of the world, mainly including the content of lead, cadmium, copper, in particular content of lead element. China was a big export country of tea, and tea was the superiorly traditional agricultural exports. Therefore, the rapid, real-time, portable, cheap heavy metal detection equipment was urgent to develop for the detection of heavy metals in tea.Compared with usually heavy metal detection methods, the electrochemical analysis was a recognized rapid, sensitive and accurate trace analysis method. The voltammetry was the most common approach in electrochemical methods to detect heavy metals, and square wave stripping voltammetry was one of the highest sensitivity way to detect heavy metals. In addition, the electrochemical sensors which was miniaturization, low cost, high sensitivity and easy to use has become one of the focuses in the rapid heavy metals detection methods. Based on this, the study was introduced the square wave stripping voltammetry technology and electrochemical sensors into rapidly detecting the lead and other harmful heavy metals in tea. We wanted to build a novel electrochemical sensor to rapidly detect the heavy metals, and provided a theoretical basis and methods experimental basis for establishing the rapid detecting method.This paper mainly contains the following aspects:The first part of the thesis summarized the heavy metals detection methods of food, and especially the electrochemical detection method was introduced detailedly. It also stated the chemometrics.The second part presented a new rapid detecting technique of trace lead in tea based on square wave stripping voltammeter of electrochemical sensor. Several factors such as pretreatment of mercury film electrodes, the concentration and pH of buffer solution, and other parameters of electrochemistry were optimized. Test results showed that the mercury film was formed after plating 300 s in the concentration of 3×10^-4 mol/L HgCl₂ solution at potential of -1.0 V. A series of best parameter are: Plating potential=-1.0 V, Estep= 3 mV, Frequency= 15 Hz, Amplitude= 20 mV, pH= 5, plating time= 100 s, balance time= 30 s. Under the optimized condition, the study result showed that the calibration curve was linear in the range of 10～800μg/L, the equation was Ip(μA)=1.029+0.105X(μg/L) with regression coefficient of 0.9976, and the detection limits was 0.45μg/L(S/N=3). The interference of other ions to 120μg/L lead was studied. The heavy metals of lead in tea samples were detected and the result was good. No significant difference between the results of GB detection method with the paired t-test comparison, and the recovery was reached 81.29% to 107.35%. The methord could be further studied.In the third part the square wave anodic stripping voltammetric (SWASV) methodology using a screen printed carbon electrode (SPCE) in situ plated in Hg²⁺ to detect lead in Green tea was built. A detailed description of the process optimization was reported. A series of best parameter are: Hg²⁺ concentration = 4×10^-4 mol/L, Plating potential= -1.1 V, Estep= 3 mV, Frequency= 10 Hz, Amplitude= 55 mV, pH= 5, plating time= 280 s, balance time= 40 s. Under the optimized analytical condition, obtained the linearity, the equation and detection limit were 10～225μg/L (r=0.9986), Ip(μA) = 0.336+0.025X (μg/L) and 0.74μg/L(S/N=3), respectively. The interference effect was studied with various others ions when detecting 120μg/L Pb²⁺. 5 sample pretreatment methods of tea to detected lead was compared. The tea was digested using microwave oven and sealed pressurization PTFE microwave digestion tank. The standard method of analysis was used to detect samples and comprised with the GB method, no significant deviation. The method was sensitive, accurate, fast and suitable for the determination of trace lead in tea. Results showed that microwave digestion method had the least loss, the minimum control value and the determination value was similar to GB. Comprehensive evaluation, microwave digestion method was optimum method in five kinds of sample pre-treatment methods in the tea which applied in SWASV to rapidly determinate the trace Lead.In the fourth part chemometrics methods were introduced into electrochemical methods to simultaneously detect Cu, Pb, Cd in mixed solution. We got the appropriate detecting parameters through the test of single heavy metal. This result showed that the stripping peak and potential changed. Therefore, the multianalysis was used to calibrate the windages. First, the prediction samples were built by the orthogonal testing. We established the testing multi-elements model which based on PCA, and through predicting the standard metal ion concentration to verify its test model. The results showed that the forecast results based on PCR and PLS testing model were better than the standards curve method. They could used as detection methods to simultaneously detect multi-elements.In the fifth part there were summary of papers and prospects. A rapid and simple method for determination of lead and other heavy metals elements was developed. It was also a new detection means for detecting heavy metals individually and simultaneously in tea.