Thiolated Conducting Polymer-modified Electrodes For Highly Sensitive Electroanalysis Of Cadmium And Lead Ions

Lead(II) and cadmium(II) are common heavy metal environmental pollutants with toxic effects on living organisms. It is important to explore sensitive, rapid and simple analytical methods for dynamic monitoring of Pb2+and Cd2+. Anodic stripping voltammetric (ASV) are widely used to detect heavy metals owing to its low cost, high sensitivity and convenience in operation. Tethering of specific chemical groups on the electrode surface can improve the detection sensitivity and selectivity of ASV. Conducting polymers have been widely used for trace detection of heavy metal ions. Thiol-tethered conducting polymers as a researching branch of the emerging thiol-ene chemistry are novel functionalized conducting polymers, but their applications in ASV analysis are not reported to date. In this thesis, we briely review the electrochemistry of conducting polymers and study thiol-tethered conducting polymers for ASV analysis of heavy metals. The main contents are as follows.1. A glassy carbon electrode modified with Bi, Nafion and2-mercaptoethanesulfonate (MES)-tethered polyaniline (PANI) was applied to sensitively detect Pb2+and Cd2+by square wave anodic stripping voltammetry. The PANI-MES interaction was examined by quartz crystal microbalance and Fourier transform infrared spectrophotometry. The electrode modification of thiolated PANI exhibits a higher analytical sensitivity versus that of pristine PANI, because the coordination of Pb2+and Cd2+with S atoms in the thiolated PANI film can improve their preconcentration efficiencies. Under optimum conditions, the linear calibration curves ranged from0.1to30μg L-1for Pb2+and0.1to20μg L-1for Cd2+, with limits of detection(S/N=3) of0.04μg L-1for Pb2+and0.05μg L-1Cd2+, respectively, after their preconcentration at-1.2V vs. SCE in pH4.0acetate buffer containing200μg L-1Bi3+for5min. This method was successfully applied for analyses of Pb2+and Cd2+in real water samples.2. Square wave anodic stripping voltammetry was applied to sensitively detect Pb2+and Cd2+at a glassy carbon electrode modified with overoxidized polypyrrole (OPPy), Nafion and Bi. The Nafion/OPPy/Au film possesses the stronger adsorbability to Cd2+and Pb2+than Nafion/Au film, as confirmed by quartz crystal microbalance (QCM) measurements. Under the optimal conditions, the linear calibration curves ranged from0.05to30μg L-1for Pb2+and0.1to25μg L-1for Cd2+, with limits of detection(SIN=3) of0.02μg L-1for Pb2+and0.04μg L-1Cd2+, respectively, This sensor was applied to the simultaneous detection of Cd2+and Pb2+in water samples with satisfactory recovery.3. Square wave anodic stripping voltammetry was applied to sensitively detect Pb2+and Cd2+at a glassy carbon electrode modified with overoxidized2-mercaptoethanesulfonate (MES)-tethered polypyrrole (OPPy-MES), Nafion and Bi. The PPy-MES interaction was examined by quartz crystal microbalance. Under optimum conditions, the linear calibration curves ranged from0.05to35μg L-1for Pb2+and from0.1to25μg L-1for Cd2+, respectively, after their preconcentration at-1.2V vs. SCE in pH4.0buffer containing300μg L-1Bi3+for5min. The detection limits (S/N=3) are estimated to be0.03μg L-1for Pb2+and0.04μg L-1Cd2+. This method was successfully applied for Pb and Cd analysis in real water samples.