Electroorganic Preparations. XXIII. Polarography and Reduction of Cinnoline and Related Compounds.

Measurement of the kinetics of adsorbed cinnoline by square-wave voltammetry

“…Between pH 2 and pH 12 the median potential is a linear function of pH, with a slope ∂Ē /∂ p H = −0.058 ± 0.003V . This is in agreement with polarographic results [21]. The median potentials of cyclic voltammograms are equal to halfwave potentials of d.c. polarograms of cinnoline.…”

“…It has been shown theoretically that there was no splitting of the net response if charge transfer was followed by a chemical reaction [26], and hence it can be concluded that in neutral solution the transformation of 1,2-dihydrocinnoline into 1,4-dihydrocinnoline can be neglected. Because of the similarity of responses, this conclusion applies not only to the basic electrolyte, where it is expected on the basis of the polarographic results [21], but also to the solution of pH 4.65.…”

“…Cinnoline is characterized by a stable double bond between nitrogen atoms [17,18,19]; this results in its low reactivity to radicals under environmental conditions [20]. On a mercury electrode in basic electrolytes cinnoline can be reversibly reduced to 1,2-dihydrocinnoline: (2) but in strongly acidic medium the redox reaction is followed by irreversible transformation of the product into 1,4-dihydrocinnoline that cannot be electrooxidized back to cinnoline [21]. In aqueous electrolytes both cinnoline and 1,2-dihydrocinnoline are strongly adsorbed by the mercury electrode surface [22,23].…”

Determination of isoniazid in human urine using screen-printed carbon electrode modified with poly-l-histidine

“…In addition, pH values higher than 9.0 were avoided since the reduction of INZ occurs very closely to the electrolyte/electrode discharge. The cathodic peak potential obtained for INZ in phosphate buffer solutions at pH values ranging from 1.0 to 11.0 have presented a shift of 54 mV by pH unit to more negative values, indicating that the electrode process is influenced by protonation reactions, as observed by other authors [15,32]. The optimum pH for INZ determination was 7.0.…”

“…The isoniazid content in these samples was determined by four successive additions of the isoniazid standard solution. represented by a cathodic peak at −0.98 V, which can be attributed to cleavage of the -HN-NH 2 linkage with the release of NH 3 , in a process involving two protons and two electrons, as demonstrated previously [32]. There is no peak on the reverse scan indicating that the process is an irreversible process.…”