Applying Immittance Spectroscopy to Monitoring Hydrogen Peroxide in the Presence of Ascorbic Acid. Part I: Theoretical Considerations

Selective Monitoring of the Hydrogen Peroxide Signal in the Presence of Ascorbic Acid. Part II: Preliminary Practical Realization of Applying Immittance Spectroscopy

“…As mentioned above, the choice of electrode material (Pt or Ir-CP) dictates the values of the heterogeneous rate constants and thus according to the theory [13], in the immittance spectrum in¯uences the differences in magnitude and phase in a comparison between analyte and interferent. Further separation and/or tuning of these differences can then be attempted by selecting the DC potential and AC frequency to be used.…”

“…Theoretical modelling of the hydrogen peroxide and ascorbic acid systems were performed on a SGI O 2 Workstation as described in Part I [13].…”

“…According to the previous theoretical examination of methods for discerning a kinetically less favored amperometric signal at a given potential in a mixed sample, AC mode operation could achieve successful selection of hydrogen peroxide (E 300 mV vs. SCE) over ascorbic acid (E 150 mV vs. SCE) [13] at potentials above the overpotential for ascorbic acid. Normally in DC amperometric measurement, it would be expected that the ascorbic acid current would be of similar magnitude or would dominate the total current in this region.…”

“…Nevertheless, both electrodes appear to ful®ll the requirement for a potential region to exist where the interferent (ascorbic acid oxidation) is diffusion-limited so that the AC current is small, while the measurand (hydrogen peroxide) is in the kinetically controlled region, so that the AC current is large (i.e., Y AA 5 Y HP ). This suggests that there may be opportunity for tailoring the AC method to discriminate the hydrogen peroxide signal as suggested by the modeling study [13]. Figure 3 shows two AC admittance spectra on the iridium and platinum electrodes for peroxide, ascorbic acid and buffer samples, comparing examples taken from the extremes of the predicted useful potential window.…”

“…Figure 4 compares the predicted admittance values for hydrogen peroxide and ascorbic acid on Pt using theoretical values equivalent to those seen in experiment at 100 mHz [13]. Since E AA1 < E HP1 , the AC admittance of peroxide remains signi®-cantly greater than that of ascorbic acid and reveals the inherent selectivity of the AC technique for the peroxide signal.…”