Polarography in initial stages of elucidation of organic electrode processes

2009 ◽  
Vol 74 (11-12) ◽  
pp. 1757-1776 ◽  
Author(s):  
Petr Zuman
Keyword(s):  
Supporting Electrolyte ◽  
Limiting Current ◽  
Thiourea Derivatives ◽  
Electrode Processes ◽  
Proton Transfers ◽  
Half Wave ◽  
Organic Electrode ◽  
Electroanalytical Method ◽  
Drop Time ◽  
Physical And Chemical

To develop a reliable electroanalytical method, it is essential to understand – at least in principle – the nature of physical and chemical processes involved. DC polarography is a useful tool in initial stages of elucidation of processes involving reductions and oxidations of organic compounds in aqueous solutions. Main information to be obtained involves: the number of reduction and oxidation steps, the number of electrons transferred in each step, the nature of the transport of electroactive species, the roles of fast, slower and slow chemical reactions (such as proton transfers or hydration–dehydration equilibria), in particular those preceding electron transfer and the structure of the electrolysis product. The used tools are: (i) Measurements of the limiting current and half-wave potentials and their dependence on composition of the supporting electrolyte; (ii) dependences on drop-time and scan-rate; (iii) product identification; (iv) comparison with structurally related compounds, experimentally and from literature. Examples of reductions of the following bonds are given. Single bonds: C–X (X = halides, OR, OH, NH2, SR), N–Y (Y = O, N, S), O–O, N–N, S–S. Double bonds: C=C, C=N, C=S, N=N, and also triple bonds: C≡C, C≡N. Examples of oxidations are those of phenols and of enediols. Anodic waves due to mercury salt formations are observed for thiols, urea and thiourea derivatives (barbiturates, thiobarbiturates), and dithiocarbamates. References are restricted to our work.

Selective Sensing Platform Utilizing Graphitized Multi-Walled Carbon Nanotubes for Monitoring of Ondansetron and Paracetamol

2020 ◽  
Vol 16 ◽  
Author(s):  
Biljana Nigović ◽  
Iva Šimunić ◽  
Ana Mornar
Keyword(s):  
Carbon Nanotubes ◽  
Cation Exchange ◽  
Supporting Electrolyte ◽  
Polymer Concentration ◽  
Fixed Dose ◽  
Sensing Platform ◽  
Multi Walled Carbon Nanotubes ◽  
Electroanalytical Method ◽  
Walled Carbon Nanotubes

Background: Ondansetron and paracetamol are often co-administrated to prevent and treat nausea and vomiting caused by anaesthesia and to control of postoperative pain. In addition, ondansetron is used as the first-line antiemetic in paracetamol overdose. Therefore, selective and sensitive method for their simultaneous analysis is of a great importance. The electroanalytical methods are highly sensitive and offer many possibilities for new sensor platform design. However, at present, no electroanalytical method for simultaneous determination of these drugs has been proposed. Objective: The aim of this study was to develop a novel nanosensor for selective monitoring of ondansetron and paracetamol in pharmaceutical and biological samples without expensive and time-consuming pretreatments. Methods: The graphitized multi-walled carbon nanotubes embedded in a cation exchange polymer matrix was selected, among various surface functionalizations evaluated, to design novel sensor. Based on its excellent sensing performance, the first electroanalytical method was developed for rapid concurrent determination of investigated drugs. Results: The scanning electron microscopy study showed interlinked nanoporous network structure and highly enlarged active surface. The developed sensor facilitated electron transfer in the oxidation of both drugs and tremendously enhanced the adsorption capacity for ondasetron, thus exhibiting significant increase of drug responses and sensitivity. To obtain much sensitive response of investigated drugs the effect of pH values of supporting electrolyte, dispersed nanomaterial amount, the cation exchange polymer concentration, drop-casting volume of nanocomposite suspension, accumulation potential and deposition time on the peak current was evaluated. The developed electroanalytical method was validated and practical utility of the proposed nanosensor was tested. Conclusion: The developed sensor is promising sensing platform with a fast response time for analysis of ondansetron and paracetamol at very different concentration levels found in their fixed-dose combination and human serum sample after recommended daily doses showing its potential usage in pharmaceutical quality control and clinical research.

Some applications of polarography for investigation of equlibria in aqueous solutions of organic compounds

2009 ◽  
Vol 74 (11-12) ◽  
pp. 1777-1789 ◽  
Author(s):  
Petr Zuman
Keyword(s):  
Aqueous Solutions ◽  
Organic Compounds ◽  
Carbonyl Compounds ◽  
Limiting Current ◽  
Nitroso Compounds ◽  
Primary Amines ◽  
Acid Base ◽  
Fast Reactions ◽  
Half Wave

There are two possibilities how to follow equilibria of organic compounds established in aqueous solutions using polarography: for very fast reactions, information can be obtained from shifts of half-wave potentials. For slowly established equilibria, the changes in the limiting current are followed. In both cases variation of the half-wave potentials or limiting currents with concentration of a reactant, present in excess, is followed. The types of reactions, which had been followed in this way, are as follows: hydration–dehydration equilibria, additions of hydroxide ion to carbonyl and nitroso compounds, the role of slowly established acid–base equilibria involving C-acids; further also reactions involving the addition of ammonia, primary amines, hydroxylamine, and hydrazine to carbonyl compounds.

scholarly journals Synthesis and polarographic studies of beta-substituted phenylcystine derivatives

1970 ◽  
Vol 48 (13) ◽  
pp. 2000-2005 ◽  
Author(s):  
R. J. Thibert ◽  
C. Patel
Keyword(s):  
Sodium Acetate ◽  
Supporting Electrolyte ◽  
Anhydrous Methanol ◽  
Ethyl Esters ◽  
Polarographic Method ◽  
Substituent Constant ◽  
Wave Potential ◽  
Polar Substituent ◽  
Half Wave ◽  
The Relationship

The synthesis of N-benzoyl-threo-β-p-substituted phenylcystine ethyl esters via azlactone intermediates is reported. A polarographic method for their determination using 0.1 M sodium acetate in anhydrous methanol as the supporting electrolyte was investigated. The relationship between the half-wave potential and the Taft polar substituent constant, σ*, was studied.

Polarography of some coordination compounds of platinum. I. Hexammineplatinum (IV) and Tris(ethylenediamine)platinum(IV) ions

1955 ◽  
Vol 8 (2) ◽  
pp. 158 ◽  
Author(s):  
JR Hall ◽  
RA Plowman
Keyword(s):  
Potassium Chloride ◽  
Supporting Electrolyte ◽  
Platinum Metal ◽  
Potassium Nitrate ◽  
Diffusion Current ◽  
Polarographic Reduction ◽  
Wave Potential ◽  
Half Wave Potential ◽  
Half Wave ◽  
Continuous Discharge

The polarographic reduction of tris(ethylenediamine)platinum(IV) and the hexammineplatinum(IV) ions has been studied in potassium chloride, potassium nitrate, and potassium nitrate plus ammonia solutions. Both ions were reduced irreversibly producing similarly shaped waves, showing well-defined diffusion current regions corresponding to two-electron reductions of the complexes. A linear relationship existed between diffusion current and concentration within the range examined. In aqueous potassium chloride and potassium nitrate media, the waves contained slight inflexions at positions corresponding to one-electron additions. The phenomenon suggested the transient presence of platinum(III) ions, and indicated that the half-wave potential of the reduction of the complexes to the trivalent state was very close to the half-wave potential of the reduction from platinum(IV) to platinum(II). The values were so close together as to indicate the improbability of isolating the trivalent complexes. Gelatin enhanced the inflexion in the wave but shifted the wave in a more negative direction. An increased concentration of supporting electrolyte also shifted the wave to a more negative position. In all cases a continuous discharge began at about -1.3 V (v. S.C.E.). This discharge was so far removed from that of the potassium ions of the supporting electrolyte that it was attributed to the discharge of hydrogen. Since the initial reduction of the platinum complexes corresponded to a two-electron change, it can be represented by reduction to a tetrammine ion. It is postulated that at higher applied potentials (namely, -1.3 V v. S.C.E.) the reduction proceeded further, producing platinum metal. This platinum metal would be in an active state, insoluble in mercury, and being on the surface, would lower the overvoltage of hydrogen leading to its discharge at a more positive potential than on a pure mercury surface. This view was supported by the fact that gas bubbles were observed at the dropping electrode when a voltage greater than -1.3 V was applied to the electrode for some time. When ammonia was added to the supporting electrolyte, a wave, without an inflexion, and corresponding to an irreversible two-electron reduction, was obtained at more negative potentials. The bivalent tetrammineplatinum(II) and bis(ethylenediamine)platinum(II) ions also gave polarograms showing the continuous discharge of hydrogen.

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