Polarographic and electrochemical studies of some aromatic nitro compounds: Part VIII. Effects of solvents and surfactants on current–voltage curves obtained with DC and differential pulse polarography

Abstract

Differential pulse polarography (DPP) is an excellent analytical method, but cannot be recommended for applications in the initial stages of mechanistic studies. Its application is also questionable in the analysis of samples containing varying concentrations of an organic cosolvent or of surface active compounds. The effect on limiting currents obtained by DC polarography and on peak currents obtained by DPP was demonstrated for reductions of various nitrobenzene derivatives. The similarity of changes in current for various nitrobenzenes enables the exclusion of the formation of adducts 01 micelles as the predominant effect. The decrease of the limiting currents in all cases is much smaller than the decrease of DPP peak currents, due to strong effects of the surfactants on the kinetics of electroreduction. For the analysis of natural products or of solutions contaiining varying amounts of organic cosolvent, the measurement of the DC polarographic limiting current is preferred. An addition of 30%# ethanol minimizes the effects of the varying concentration of surfactant on both DC polarographic limiting and DPP peak currents.

Electrochemical Characterization of Tacrine, an Antialzheimer's Disease Drug, and Its Determination in Pharmaceuticals

“…The peak current in DPP depends on all these factors, but additionally also on the rate constant of the electrode process and on the transfer coef®cient. These aspects have also been noted by Zuman and Rupp [20] in recent work; we agree with their conclusion in the sense that, in order to obtain mechanistic information, limiting currents by DC or tast polarography are preferred. Consequently, we privilige the information obtained in Figure 6B in order to conclude about the pHdependence of the limiting current.…”

Half a Century of Research Using Polarography

“…If concentrations of substances are too low for the use of dc polarography, limiting currents obtained by normal pulse polarography can be used instead. Peak currents, obtained by differential pulse polarography (DPP), by ac polarography, or by linear sweep voltammetry (236,237), are namely also a function of the rate of the electrode process, which can be affected by adsorption of surface active compounds. In the presence of surfactants the peak currents are not only a function of concentration of the studied substance but also of the concentration of surface active materials, which can be variable.…”

Electroanalysis of Nitro and Amino Derivatives of Polycyclic Aromatic Hydrocarbons

“…In the presence of a neutral or cationic surfactant or a higher concentration of alcohol, the first wave in polarography is a four-electron wave and the second one a two-electron reduction [103,[110][111][112]. In the absence of surfactants, the first wave corresponds to a number of exchanged electrons between 4 and 5, but the sum of the first and second wave remains constant.…”

“…For NPAHs, such voltammetric behavior is also observable at mercury electrodes, partly as intramolecular [113] and partly as intermolecular (e.g., in 2,2'-dinitrobiphenyl (10) [114,115]) interactions during transformations of the nitro groups in the protic media. CV of nitrobenzene (17) in the presence of sodium dodecyl sulfate or high concentrations of N,N-dimethylformamide (DMF) gives a one-electron peak (formation of the nitro anion radical (19)) followed by a three-electron peak (formation of the hydroxylamine (26)), whereas in the presence of cationic or neutral surfactants, a four-electron peak is found at the hanging mercury drop electrode (HMDE) [110][111][112].…”