Polarimetric method

For any liquid, the extent of the rotation is proportional to the thickness of the layer traversed by the light. Further, the angle for one and the same substance depends on.  

The concentration of the solution. In some cases angle and concentration are proportional, but in others there is more or less divergence. 

The temperature. This has a small influence with some substances, and a large one with others, and the change may be in either direction. Rotations are usually referred to 20° C. 

The nature of the solvent. Other conditions being equal, the rotation sometimes changes with the solvent. 

Some active substances exhibit different rotations according as the solution is freshly prepared or otherwise, a constant value being attained only after the lapse of some time. This phenomenon is termed mtdarotation. 

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The third method is of limited application and is used only in special cases, The second is the most accurate and rapid method, and is of considerable technical importance. The chemical method (described below), although less accurate than the polarimetric method, is of great value for the estimation of sugars in biological fluids. In fact, for such purposes, it is often to be preferred to the polarimetric method owing to the probable presence of other substances having high optical rotations. 

The isotopic quasi-racemate or differential polarimetric method is a kinetic... 

Another polarimetric method for the accurate determination of KIEs bears a strong resemblance to the isotopic quasi-racemate method, described above. In this method, Bach and co-workers (1991) utilized what they called isotopically engendered chirality to determine the primary deuterium KIE for an elimination reaction. In theory, the method can be used for any reaction where a substrate with a plane of symmetry yields, under normal conditions, a racemic mixture. For instance, if the plane of symmetry in the unlabelled... 

It is worth noting that the KIEs determined by this polarimetric method are in excellent agreement with those found by the classical mass spectrometric method. Also, as the authors pointed out, the method can be extended to the measurement of secondary deuterium and even heavy-atom KIEs. 

The polarimetric method, in combination with the results of chemical correlation, made it possible to determine the optical purity of a range of chiral sulftnates (105-107), thiosulfinates (35,105), and sulfinamides (83) with the sulfur atom as a sole center of chirality. These compounds were converted by means of Grignard or alkyl-lithium reagents into sulfoxides of known specific rotations. This approach to the determination of optical purity of chiral sulfinyl compounds has at least two limitations. The first is that it cannot be applied to sterically hindered compounds [e.g., t-butyl /-butanethio-sulfinate 72 does not react with Grignard reagents]. Second, this... 

Dolezalova, M. and Tkaczykova, M., Direct high-performance liquid chromatographic determination of the enantiomeric purity of levodopa and methyldopa comparison with pharmacopoeial polarimetric methods, J. Pharm. Biomed. Anal., 19, 555, 1999. 

The polarimetric method is sometimes useful for the study of exchange reactions in which large rotation changes but no net chemical change is involved... 

This polarimetric method was made even more general by utilizing chiral HPLC techniques. The L-UNCAwas dissolved in the solvent at a concentration of 0.33 M at 20 °C. The tertiary amine (1.5 equiv) was added at time zero. The solution was allowed to stand for an experimentally determined delay time, during which the only process that can occur was epimerization, since there is no nucleophile present. The delay time was determined after carrying out several experiments with different delay times and chosen so as to fall within or just after the first half-life for racemization. At the end of the delay period, benzylamine was added. Benzylamine is a very powerful nucleophile that reacts virtually instantly (regardless of the type of activation) with the resulting mixture of l- and d-UNCAs to form the benzyl amides and quench the epimerization process. Thus, a snapshot of the ratio of l/d activated intermediates at the instant of benzylamine addition was obtained by measurement of the l/d ratio of the benzyl amide products. 

AOAC 975.43 Identification of RRR- or all-rac-alpha-Tocophcm in Drugs and Food or Feed Supplements, Polarimetric Method (First Action 1975 and Final Action 1980)... 

The object of this determination, which is carried out principally with sweet wines, is to estimate the reducing sugars and any saccharose which may have been added to the wine. Both the optical and chemical methods are used (see also Sugars, General Methods). The polarimetric method is also sometimes used with sweet wines in order to ascertain if dextrin or commercial glucose has been added see later, p. 196). 

The development of accurate methods for the determination of enantiomeric purity, which began in the late 1960 s, has been critical for the assessment of enantioselective synthesis. Thus a prerequisite in the enzyme-catalyzed kinetic resolution of racemates is a precise and reliable assessment of the degree of enantioselectivity (E), enantiomeric excess (ee) and conversion (c). Among these methods are 1) polarimetric methods, 2) gas chromatographic methods, 3) liquid chromatographic methods and 4) NMR spectroscopy. The most convenient and sensitive methods used are chiral GC and HPLC. 

During the past few years four methods have been developed for the study of the kinetics of oxide film formation, all being semicontinuous in nature. The polarimetric method has been adapted by Lustman and Mehl (14) for the measurement of the oxidation of copper. A spectro-photometric method has been applied by Waber, Sturdy, Wise, and Tipton (15) to the study of the oxidation of tantalum while a differential pressure method has been developed by Campbell and Thomas (16) for a study of the oxidation of a series of metals and alloys at elevated temperatures. We have chosen to use a sensitive weight gain method (17,18) in which a quartz microbalance is placed directly in the vacuum system. 

The rate of the interconversion may also be followed by measuring the change in volume or in refractive index. Such measurements give rate coefficients identical with those obtained by the polarimetric method. In Table XVIII, rate coefficients for the mutarotation of a number of sugars are listed. The rates of mutarotation of several sugars (for example, D-ri-bose, D-galactose, and all the ketoses) do not obey the first-order law. Their complex mutarotations result from the presence in solution, in appreciable concentrations, of more than two species. In addition to pyranoses, there must be present either furanoses or acyclic forms, or both. 

Over the last twenty years , there has been a resurgence into the measurement of acidity of organic molecules and its associated solvent effects (e.g. in heptane, cyclohexane , THF and cyclohexylamine ). These have generally been measured using close comparison indicators of known pX, determined by colorimetric, spectroscopic and polarimetric methods " . The carbonyl (C=0) group with its a- and... 

If the nitroglycerine it suspected to contain compounds such as dinitrochlorhydrin, it may be examined by specific gravity, nit en content, chlorine content, refractive index, Nitrosugan increase the viscosity and lower the nitrogen content. Hoffman and Hawse give a polarimetric method for nitrosugars. 

Ergotamin [a]20°/D = -155° and Ergotaminin [a]20°/D =-i-381°), it is easy to control the separation of the two alkaloids by means of the polarimetric method. It is also possible to control the separation of the alkaloids by irradiating their solutions with ultraviolet light, as it is known that in this light the ergot-alkaloids possess a violet to blue fluorescence. 

Rate constants reported by Riiber and Sorensen and by Whistler and Rowell have been converted from common logarithms into natural logarithms. In 0.6 N hydrochloric acid at 75° (polarimetric method). 

Polarimetric method, kois the rate constant for the hydrolysis of the parent glycoside, that is, methyl o-D-glucopyranoside or methyl a-D-mannopyranoside, under the same conditions. 

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