| The dissertation developed a novel polyvinyl chloride (PVC) membrane modified electrode and studied the electrochemical behaviors and the effect of surfactants on the electrochemical behaviors of the modified electrode. The proposed modified electrode could also directly be used to determine trace surfactants in environmental water samples. The main points of the dissertation were as follow:(1) The cyclic voltammograms (CVs) of the PVC membrane modified electrode showed that the peak currents increased with the number of scans and finally remained constant after 2 h. It was owing to the fact that the holes of PVC membrane swelled with time and the activate substances diffused to the surface of the modified electrode became faster with time. Such experimental results revealed that the redox process had the characteristics of electrode/membrane interface reaction. It also indicated that the prepared PVC membrane modified electrode was stable.(2) The peak potentials were removed negatively and both the oxidative currents (Ipa) and the reductive currents (Ipc) deceased with the increasing pH values of supporting electrolyte. When pH=12～14, the relationship between the potentials (E0)and pH values was E0= [Epa+Epc] /2. Thus, the electrochemical process of activate substance in the PVC modified electrode could be expressed as follow: Further experiments illustrated that the differences of the peak potentials (△Ep) were increased with the square of the scan rates, Ipa= (0.0201v1/2+0.9711)A,R2=0.9711,which indicated that the redox process was diffusion-controlled. Moreover, the oxidative currents (Ipa) were higher than the reductive currents (Ipc), which indicated that the redox process was a quasi (half)-reversible process.(3)Cyclic voltammograms, chronoamperometry, the steady state polarization curves and alternative current impedance spectroscopy were used to study the effect of cationic (ethylrimethylammonium bromide, CTAB), anionic (sodiumdodecylsulfate, SDS) and nonionic (alkyl polyethoxyate, AEO9) surfactants on the electrochemical behaviors of PVC membrane modified electrode. Experimental results revealed that when CTAB or SDS was added into 0.1 mol/LKOH solution, the diffusion coefficients of both oxidation and reduction forms of Ag[B(ph)4] in the membrane of PVC were decreased and the characteristics of the diffusion controlled electrode reaction were strengthened, which indicated that the rate of electron transfer in PVC membrane was increased. However, when AEO9 was added into 0.1 mol/L KOH solution, the diffusion coefficients of both oxidation and reduction forms of Ag [B(ph)4] in the film of PVC membrane were increased and the characteristics of the diffusion controlled electrode reaction were weakened, which indicated that the rate of electron transfer in PVC membrane was decreased. Therefore, cationic and anionic surfactants could enhance the electrode reaction of the PVC membrane modified electrode. Whereas, the nonionic surfactants could restrained the electrode reaction of the PVC membrane modified electrode.(4) The dissertation proposed method could directly determine the trace amounts of surfactants using PVC membrane modified electrode as working elelctrode based on the relationship between the peak currents of different pulse voltammogram and surfactant concentration.. the liner concentration range of surfactants of AEO9,SDS and CTAB were 0.4235nmol/L～22.86nmol/L, 13.2nmol/L～269.911nmol/L and 0.802nmol/L～18.211nmol/L , respectively. The detection limits of surfactants of AEO9,SDS and CTAB were 2.12×10-2nmol/L, 7.639nmol/L and 0.508nmol/L, respectively. When study the influences of those co-existing substances on the determination of surfactants in nature water samples, it was found that all the studied co-existing substances could be tolerated in considerable amounts. The proposed method offered the advantage of simplicity, rapidity, sensitivity and selectivity and it has been successfully used for determining the trace amounts of surfactant in practical environmental water samples. |
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