Quantitative analysis from retention

It follows that measurements must be made with a precision of about 0.2 second if quantitative results are to be of any value. It is seen from figure 4 that the experimental points lie very close to the line and a fairly accurate measurement of the distribution of the two isotopes can be obtained from retention time measurements. This method has very limited areas of application and is given here, more to demonstrate the effect of unresolved impurities on retention time, than to suggest it as an alternative to adequate chromatographic resolution. In some cases, however, particularly in the analysis of isotopes, it may be the only practical way to obtain a quantitative evaluation of the mixture by a liquid chromatographic method. 

The simplest model phase in reversed-phase liquid chromatography (see Section 6.5) was not satisfactory for the quantitative analysis of the retention behavior of benzoic acid derivatives in silica. Therefore, several model phases were constructed and the energy values of their optimized structures were calculated using the MM2 program. The chromatographic retention data from ref. are listed in Table 6.8. 

The octanol-water partition coefficient scale may not be the best tool for hydrophobicity evaluation. The ability of MLC for hydrophobicity measurement and some studies on quantitative structure retention activity relationships (QSAR) are described in Chapter 9. Chapters 10 and 11 contain selected examples of applications in the analysis of a variety of samples, especially pharmaceutical preparations and physiological fluids, some of them are taken from the authors own experience. Details on the nature of the sample, stationary phase, mobile phase composition, detection wavelength, and figures of merit, are tabulated at the end of each of these... 

We have also added an entirely new section dealing with semi-microanalysis. In our original Introduction (p. ix) we justified the retention of macro-methods of quantitative analysis on the grounds that they formed an excellent introduction to micromethods and also afforded a valuable training in exact manipulation generally. By now, however, the macro-estimation particularly of carbon and hydrogen and of nitrogen has disappeared entirely from most laboratories. On the other hand, the micro-... 

A normal-phase HPLC separation seems to be useful to separate major chlorophyll derivatives, but it is not compatible with samples in water-containing solvents an additional extraction step is required to eliminate water from the extract since its presence rednces chromatographic resolution and interferes with retention times. Besides that, the analysis cannot be considered quantitative due to the difhculty in transferring componnds from the acetone solution into the ether phase. On the other hand, an advantage of the normal-phase method is its efficacy to separate magne-sinm-chlorophyll chelates from other metal-chelated chlorophyll derivatives. ... 

Perhaps the most revolutionary development has been the application of on-line mass spectroscopic detection for compositional analysis. Polymer composition can be inferred from column retention time or from viscometric and other indirect detection methods, but mass spectroscopy has reduced much of the ambiguity associated with that process. Quantitation of end groups and of co-polymer composition can now be accomplished directly through mass spectroscopy. Mass spectroscopy is particularly well suited as an on-line GPC technique, since common GPC solvents interfere with other on-line detectors, including UV-VIS absorbance, nuclear magnetic resonance and infrared spectroscopic detectors. By contrast, common GPC solvents are readily adaptable to mass spectroscopic interfaces. No detection technique offers a combination of universality of analyte detection, specificity of information, and ease of use comparable to that of mass spectroscopy. 

A chromatographic separation step provides various advantages to the analytical procedure (i) each component is isolated from the others (which facilitates identification) (ii) minor components in mixtures may be detected more readily than by direct analysis techniques (iii) the chromatographic retention parameter provides additional confirmation that a particular component is present or absent and (iv) quantitative analysis. However, chromatography alone does not provide information on the identity of a totally unknown sample. 

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