Normalized potential sweep voltammetry: Part III. Elimination of the effect of uncompensated Resistance and the application to heterogeneous kinetics of rapid charge-transfer processes

Uncompensated resistance (R_u) has a distoring effect on normalized potential sweep voltammetry (NPSV) slopes. This provides a simple and effective method to determine R_f^o, the value of the potentiostat feedback resistance necessary for full compensation. If the NPSV range is divided into overlapping segment, 1 and 2, corresponding to I_N of 0.20–0.50 and 0.50–0.80 respectively, the slopes m₁ and m₂ differ significantly when R_f differs form R_f^o. The difference, m₁-m₂, is negative for R_f<R_f^o and positive for R_f>R_f^o. Fine tuning of the potentiostat R_f setting so that the average value of the difference is the theoretical value can be accomplished in a minimum of time. Under these conditions, m₁ and m₂, as well as m_T, the slope of the entire correlation have very nearly the same values. Linear equations were derived from theoretical data which allow heterogeneous rate constants to be obtained directly from NPSV slopes. The precision in the NPSV slopes was observed to be of the order of ±0.002 which implies that the method should give reliable rate constants as great as 10cm s^? at a voltage sweep rate of 100V s^?1. The method is demonstrated using the reduction of benzonitrile and perylene in N,N-dimethylformamide and acetonitrile as examples.