Titration polarographic methods

Aqueous titration with IN sodium hydroxide is the usual malic acid assay. Maleic and fumaric acid are deterrnined by a polarographic method. Analytical methods have been described (40). 

Electrochemical analytical techniques are a class of titration methods which in turn can be subdivided into potentiometric titrations using ion-selective electrodes and polarographic methods. Polarographic methods are based on the suppression of the overpotential associated with oxygen or other species in the polarographic cell caused by surfactants or on the effect of surfactants on the capacitance of the electrode. One example of this latter case is the method based on the interference of anionic surfactants with cationic surfactants, or vice versa, on the capacitance of a mercury drop electrode. This interference can be used in the one-phase titration of sulfates without indicator to determine the endpoint... 

Polarographic methods can be used to estimate the equivalence point of a reaction, provided that at least one of the participants or products of the titration is oxidized or reduced at the microelectrode. When the potential applied across the two electrodes is maintained at some constant value, the current may be measured and plotted against the volume of the titrant, thus, the term amperometric titration. In the case of working electrode-reference electrode pair, the potential of the indicator electrode is maintained at a constant value with respect to a reference electrode, measuring a limiting current, which is proportional to the concentration of one or more of the reactants or products of the titration. 

Voltammetric and polarographic methods were, and still are, only exceptionally used for determining the main component of a sample (pure substance determination) since the accuracy of about 2 to 3% is not sufficient here. The other electroanalytical methods, e.g. coulometry and coulometric titrations are to be recommended here because of their higher accuracy. 

It is surprising, that the European Pharmacopoeia in contrast to the United States Pharmacopoeia has not yet introduced polarographic methods (see Table 2). Only biamperometric endpoint indications, e.g. in the titration of sulphonamides, are given. One convincing advantage of polarography is the fact, that the current signal is calculable, if the reduction or oxidation mechanism is known. 

The main advantage of manual instruments is that they are relatively inexpensive, and possess an educational value demonstrating clearly the principles of the polarographic method. The manual instruments can furthermore be advantageously applied to polarometric titrations. 

Miscellaneous Procedures. Most of the other procedures for the determination of —SH groups are variants of the processes indicated above. Of particular interest are the several amperometric titration procedures which, in effect, depend on mercaptide formation. Polarographic methods have also been used. An interesting submicro method for cystine by a Cartesian diver technique has recently been developed the method depends on the catalytic effect of —SS— groups on the decomposition of azide ion to nitrogen (78,94). The method cannot be applied to the direct determination of —SH groups. 

Anal. detn. by GLC (1939), by colorimetric method with diphenylcarbazone (490), with cacotheline after NaaOa fusion (155), by electrometric titration, investigation of hydroxocomplexes (2232), by potentiometric titration (I7OI, 2013), by polarographic method (2265). 

The methods dependent upon measurement of an electrical property, and those based upon determination of the extent to which radiation is absorbed or upon assessment of the intensity of emitted radiation, all require the use of a suitable instrument, e.g. polarograph, spectrophotometer, etc., and in consequence such methods are referred to as instrumental methods . Instrumental methods are usually much faster than purely chemical procedures, they are normally applicable at concentrations far too small to be amenable to determination by classical methods, and they find wide application in industry. In most cases a microcomputer can be interfaced to the instrument so that absorption curves, polarograms, titration curves, etc., can be plotted automatically, and in fact, by the incorporation of appropriate servo-mechanisms, the whole analytical process may, in suitable cases, be completely automated. 

Zhan and Mao [60] used a simple, fast, and selective alternating current oscilloscop-ic polarographic titration method for the determination of primaquine and other alkaloid phosphate in pharmaceutical preparation. The titration was carried out with a standard lead solution in hexamethylene tetramine buffer containing 1 M sodium chlorate (pH 5.5). The results obtained by this method are comparable to those obtained by pharmacopoeial method. 

Oxidative stress Lipid oxidation Oxygen absorption Manometric, polarographic Diene conjugation HPLC, spectrophotometry (234 nm) Lipid hydroperoxides HPLC, GC-MS, chemiluminescence, spectrophotometry Iodine liberation Titration Thiocyanate Spectrophotometry (500 nm) Hydrocarbons GC Cytotoxic aldehydes LPO-586, HPLC, GC, GC-MS Hexanal and related end products Sensory, physicochemical, Cu(II) induction method, GC TBARS Spectrophotometry (532-535 nm), HPLC Rancimat Conductivity F2-iP GC/MS, HPLC/MS, immunoassays... 

Implementation Confirmation of the in situ monitors results is obtained when river water samples are brought to the lab and tested for dissolved oxygen using a lab dissolved oxygen probe (a polarographic electrode-based measurement) and the classic Winkler oxygen titration method. 

Amperometric titration is a better method than polarographic methodfor quantitative analysis. 

The entire subject of amperometric titrations has been reviewed in a number of monographs on electrochemistry 4-6 a definitive work on this subject also has been published.7 Because the amperometric titration method does not depend on one or more reversible couples associated with the titration reaction, it permits electrochemical detection of the endpoint for a number of systems that are not amenable to potentiometric detection. All that is required is that electrode conditions be adjusted such that either a titrant, a reactant, or a product from the reaction gives a polarographic diffusion current. 

Refs. [i] Kolthoff IM, Lingane JJ (1952) 2nd edn. Polarography. Polarographic analysis and voltammetry. Amperometic titrations. Interscience, New York, vol. 2, pp 887 [ii] Heyrovsky J, Kuta J (1966) Principles of polarography. Academic Press, New York, pp 267 [Hi] Classification and nomenclature of electroanalytical techniques (1976) Pure Appl Chem 45 81 [iv] Bard AJ, Faulkner LR (2001) Electrochemical methods, 2nd edn. Wiley, New York, pp 437... 

Sc CA 65, 12854(1966) (Polarographic detn of NGu) 13) H. Opel Sc W. Ardelt, ZChem 7 (11), 439-40(1967) Sc CA 68, 46066(1968) [(Analysis of cyanamide derivatives. III. Determination of NGu) (Method is polarographic dilution titration with borax buffer and Na sulfite — compares well with titanous chloride method)]... 

The simplest methods of HTSC analysis are based on the determination of the products of sample dissolution in acidic media. Potentiometric, amperometric, or coulometric titrations are frequently used (mainly for YBCO ceramics [525-527] and their analogs with other rare-earth elements [528, 529], and also for BSCCO [530]). We note particularly the method of potentiostatic coulometric analysis [531], which allows one to analyze thallium cuprate samples over a wide range of the Tl/Cu ratio, and also the method of flow-through coulometry for determining the effective valence of copper [532]. The polarographic determination of Cu content in the samples obtained by dissolving HTSCs in concentrated alkaline solutions with special... 

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