The separation of overlapping peaks in cyclic voltammetry by means of semi-differential transformation

Abstract

A method for extracting single peaks from complex linear sweep and cyclic voltamperograms is presented. Voltamperograms are transformed by means of semidifferentiation, then all undesired peaks are removed from the semiderivative curve and replaced by calculated baselines. The resulting curve is ~~nte~ated back, giving a vol~m~~gram with one peak only. Baselines in the semiderivative domain are determined by the least-squares curve-fitting of datapoints from peak border regions, using the equation that describes the semiderivative peak of a reversible electrode process. With this procedure peaks can be removed without assumptions about the mechanism of the underlying electrode reaction. Due to its design, the algorithm presented is suitable for the fully automatic processing of cyclic and linear sweep voltamperograms. Performance of the procedure was checked with generated reversible voltamperograms as well as in real experiments with both reversible and irreversible systems. The smallest distance between two peaks of equaI height, for which the described method can yield correct results, has been found to be 110 mV for a reversible one-electron process at 298 K. This procedure can also be applied to the elimination of the cathodic current from the cyclic voltamperogram of a single component in order to get a pure anodic current value, free from cathodic contribution, or vice versa.

Semi-differential analysis of irreversible voltammetric peaks

“…Mathematical methods based on semi-differentiation and semi-integration offer an interesting alternative to classical analysis of voltammetric curves [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Various electrochemical processes, such as redox reactions with reduced and oxidised species present in the same phase [6,14,[21][22][23][24][25][26][27][28][29][30][31][32][33][34][35], adsorption on surfaces of electrodes [36][37][38], electrodeposition [39][40][41][42][43][44][45][46][47]…”

“…Application of such procedure is very helpful for separation of overlapped voltammetric peaks, the benefits depend on the extent of their overlapping. Thus, obtained semi-derivative peaks could be completely separated or may overlap [2]. Even if overlapped, however, the semiderivative peaks are usually easier to distinguish as compared with their voltammetric precursors and are more convenient for further evaluation.…”

“…Even if overlapped, however, the semiderivative peaks are usually easier to distinguish as compared with their voltammetric precursors and are more convenient for further evaluation. A further analysis of overlapped semiderivative signals should include their deconvolution by means of fitting with appropriate mathematical functions derived for a certain type of the electrochemical reaction [2].…”

“…fractional differentiation with the order of 0.5, can be represented for the electrochemical purposes as Eq. (1) [2,4,61]:…”

“…In such case, the accuracy of the peak fitting is better for the semi-derivative curve than for its voltammetric precursor with hardly distinguishable components. Deconvolution by fitting whole voltammetric curves is most effective for bell-shaped voltammetric signals which are easier to separate due to well-defined end and lack of the diffusive tail [2,67]. Such type of peaks is observed, e.g.…”