The Electrochemical Study Of Interaction Between Surfactants And Organic Compounds At Metal Electrodes

Surfactants are widely applied in electrochemistry and electroanalytical chemistry, especially in experiments to determine some metal ions using polarographic methods, in which surfactants are added in to enhance the detection sensitivity. In recent years, it has been found that surfactants are able to enhance the accumulation of some electroactive compounds at electrodes and decrease the detection limit. However, most electrodes used in these researches are non-metal electrodes, in this dissertation we use gold and silver electrodes to carry out the following researches:1. The influence of the anionic surfactant sodium dodecylsulfate (SDS) on accumulation of ethopropazine (EPZ) at a polycrystalline gold electrode has been studied. EPZ exhibits an anodic peak at about 0.67 V (vs. SCE) and a shoulder in pH 3.5 citric acid-biphthalate buffer solution. In the absence of SDS, the peak is small and ill defined, but it becomes high and well defined when SDS is added. This results from the adsorption of EPZ in the SDS membrane, which forms spontaneously on the gold electrode surface. For both cases EPZ shows the same electrode reaction mechanism, which is similar to that of promethazine (PMZ). The influence of other factors, such as pH value, variety and concentration of buffers, other surfactants, accumulation potential and time etc has been discussed. It was found that only anionic surfactants were of enhancement effect on the EPZ accumulation. And the solution should be acidic or neutral so as to maintain the interaction due to its electrostatic nature. The optimum SDS concentration for EPZ accumulation is about 0.1 mM regardless of whether or not an accumulation potential is adopted. When all the experiment conditions are optimized, the peak current of the anodic peak changes linearly with the concentration of EPZ over the range of 0.4 ~ 4 M, thus it is of analytical significance.2. An electrochemical study of deposit membrane of L-glutathione (GSH) and cetylpyridinium bromide (CPB) at polycrystalline Ag electrodes has been carried out. It is found that a deposit membrane can form at the Ag electrode after deposition at 0.05 V (vs. SCE) in a mixed solution of GSH and CPB. This deposit membrane gives a good-shapedcathodic peak at about -1.1 V, accompanied by the appearance of multiple anodic peaks. Further investigation suggests that the cathodic peak should be mainly attributed to the reduction of CPB rather than the reductive desorption of GSH. The influences of deposition potential, deposition time, CPB concentration, pH and concentration of base solution, other surfactants and the transfer experiment of deposit membrane were all investigated, which supply some information on the formation of the deposit membrane. Many thio compounds and surfactants have been used for comparison. It is found that both the mercapto group and carboxy group play important roles in the formation of the mixed deposit membrane.