Differential-pulse adsorptive stripping tensammetry: Enhancement of the analytical signal through the application of external resistance

The DP technique was developed to improve the faradaic/capacity current rel ation, i.e., a signal-to-noise ratio, when an analyte is reduced or oxidize d. Surprisingly, DP, without any pulse rearrangement was successfully appli ed to the determination of electroinactive organic substances utilising ten sammetric measurement, i.e., noise in terms of DP measurement principles. H owever, analytical signals recorded by the DP technique are weaker than tho se in the AC technique. In order to optimize the tensammetric analytical si gnal in DP measurements, the dependence of the capacity current on the resi stance of an electrical circuit has been investigated, both theoretically a nd experimentally. This dependence expressed by the equation: i(c) = (Delta E/R) exp(-t/RC), with capacity current i(c), pulse amplitude DeltaE, pulse time t, resistance R, capacity C,has a maximum corresponding to the conditi on: R = t/C. Experimental verification was done on the example of a solutio n of ethyl acetate using aqueous Na2SO4 of various concentrations as a base electrolyte or 0.5 M Na2SO3 and an external resistance. In both cases, as was predicted, the analytical signal strongly reacts on the changes in elec trical resistance and goes through a maximum. However in the case of sodium sulfate solution, the oxygen signal coincides with the ethyl acetate peak. A properly selected external resistance enables the enhancement of a tensa mmetric signal by more than one order of magnitude. Experimental values of the capacity current vs. external resistance dependence are in close agreem ent with those calculated.