D. Stočesová

Bio: D. Stočesová is an academic researcher. The author has an hindex of 1, co-authored 1 publications receiving 41 citations.

Polarographic and electrochemical studies of some aromatic and heterocyclic nitro compounds, part I: General mechanistic aspects

Abstract: Comparing reduction potentials of aromatic nitro compounds with those of corresponding nitroso compounds, by studying shifts of half-wave and peak potentials with pH and by following the decrease of limiting current in buffered 35% DMF-water mixtures, the sequence of protons and electrons in the four-electron reduction step was proved to be: H+, e, H+, e, 2e, 2H+. Arylhydroxylamines formed in the four-electron reduction of nitro compounds can be protonated and further reduced, they can undergo dehydration (provided that the dehydration product is stable), they can undergo chemical reactions with intermediates of the reduction of the nitro group, like ArNO, they can be electrooxidized to nitrosobenzenes (which can undergo chemical reactions) or they can react with carbonyl groups when present. Stabilization of the dehydrated form can occur in quinonemethide (nifedipine) or in some quinone-like heterocyclic derivatives. Side reactions of ArNHOH and ArNO are demonstrated by smaller peaks in CV and by controlled potential electrolysis. Reactions of ArNHOH with carbonyl groups were observed by formation of new waves of nitrones in the reduction of nitrobenzenaldehydes.

Fabrication and Use of Pyrolytic Graphite Electrode for Voltammetry in Aqueous Solutions.

Abstract: A pyrolytic graphite indicating electrode was fabricated and applied to voltammetry in aqueous solutions. In either acid chloride or acid nitrate medium, it has a useful range of potential from +1.0 to -0.8 volt vs SCE. Reducible ions that have decomposition potentials in this range can be determined. No treatment of the electrode other than a preliminary cleaning is required prior to or during its use. The following ions were determined at the 10/sup -3/M concentration level: Ag(I), Hg(I), Cu(II), UO/sub 2/(II), Fe(III), and Sn(IV). The E/sub 1/2/ and i/sub d//C values are reproducible. The precision obtained in measurements of the various ions is comparable with that of polarography. The voltammetric curves recorded at a scan rate of O.1 volt/minute are characterized by a definite plateau rather than a peak. A reliable and rugged electrode of any reasonable area can be prepared by the technique described.

Voltammetric Behavior of p‐Nitrophenol and Its Trace Determination in Human Urine by Liquid Chromatography with a Dual Reductive Mode Electrochemical Detection System

Abstract: The determination of trace p-nitrophenol (PNP) concentrations in human urine has been successfully achieved by high performance liquid chromatography dual electrode detection (LC-DED) in the reduction-reduction mode. Initial cyclic voltammetric studies were undertaken to investigate the electrochemical behavior of PNP at a glassy carbon electrode over a wide pH range; the redox processes giving rise to the signals have been deduced. Further, deductions regarding the behavior in the flow cells were made from hydrodynamic voltammetric data. PNP eluting from the analytical LC column is first reduced to p-hydroxylaminophenol, at the first generator electrochemical cell. This species then undergoes chemical oxidation to give a quinoneimine species which is then detected at the downstream detector electrode using an applied potential of -0.1 V. The optimum chromatographic mobile phase consisted of 40% acetonitrile, 60% water, containing 25 mM o-phosphoric acid, at a flow rate of 0.5 mL/min; this was used in conjunction with a Hypersil C-18 column. Hydrodynamic voltammetric studies were undertaken to investigate the dual electrode behavior of PNP, and an applied potential of -2.0 Vat the generator cell and -0.10 V at the detector cell were found to be optimum. The response was found to be linear over the range 7.0 ng to 500 ng on column, with an associated R-2 value of 0.9981; the limit of detection was found to be 1.0 ng PNP on column. No interferences were seen for a number of common drugs or for the principal electrochemically active components of human urine or serum. The developed assay was successfully applied to the determination of trace concentrations of PNP in human urine samples, exhibiting coefficients of variation of 7.1% (n =7), with a mean recovery of 94.7% for urine fortified at 522 ng mL(-1).