Evaluation of chromatograms

The previous section gives an overview of the experiments necessary to determine the model parameters. This section describes general procedures for evaluating parameter values from experimental data. Model parameters are deflned in Chapter 2, while Section 6.2 shows how they appear in the model equations. Based on the assumptions for these models it follows that all plant effects as well as axial dispersion, void fraction, and mass transfer resistance are independent of the adsorption/desorption processes occurring within the column. 

The following methods are useful and required for the evaluation of model parameters moment analysis, HETP plots, and peak fltting. 

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Evaluation of chromatograms 133 ff -, optical trains 30, 39 -, peak area/height 31, 33,40 Evipan 339, 343... 

Evaluation of chromatograms la 133ff Evaluation, peak area or height la 31,33,40 -, optical trains la 30, 39 Evipan la 339,343 Excitation to fluorescence la 10,12,20,37 Explosion resulting from reagent residues la 82,253,261,315,365 Explosives lb 49,244,407-409 Exposure to vapors la 86... 

Besides, IR-spectroscopy, reflectance spectroscopy, spark chamber method etc., may also be employed for the direct evaluation of chromatograms. 

Since the work of Manley and Shubiak (182), who were the first to apply HPLC to anthocyanin analysis, numerous HPLC techniques have been developed for the separation and quantification of anthocyanins and anthocyanidins. Nowadays HPLC has become the method of choice, because it offers the advantage that it is a rapid, sensitive, and quantitative method. For the peak identification and quantitative evaluation of chromatograms, the use of pure anthocyanin standards is recommended however, only a limited, but constantly increasing, number of substances is avail-... 

The greatest error associated with the direct evaluation of chromatograms is in the chromatographic process itself. Errors arise from the application of the initial spots to the plate, from the separation process and from the treatment of the final separated spots prior to evaluation. The spotting error is often the most common cause of poor reproducibility. Creep back , a term describing the tendency for some of the spotted solution to run up the outside of the needle during spotting, is frequently encountered. This quantity of solution may be lost to the spot and could be deposited with the next. The... 

At the quantitative evaluation of chromatograms the peak areas At or quantities proportional to the peak area are related to the amount Qt of the individual sample components ... 

More recently, electronic eqmpment used in other areas of science has been used in TLC for the evaluation of chromatograms. This includes the flat-bed scanner, which is often used in conjunction with special software for the evaluation of DNA electrophoresis results. However, the direct use of flat-bed scanners in TLC is limited to the evaluation of colored chromatograms, and the author is not aware that any work on this theme has yet been published. 

In today s industry, digital cameras have replaced most video systems. All information about the illumination system, data processing equipment and image output system given in Section 7.3 also apply here. Only the current software determines how to achieve a qualitative and/or quantitative evaluation of chromatograms. For the topic Digital Camera see Documentation , Section 8.5. 

Figure 73. Evaluation of chromatograms of two active ingrecHeiits with different absorption properties in short-wave UV light...

However, this method can be used only for the evaluation of chromatograms with symmetric peaks. The advantage of the method is that the chromatogram can have symmetric peaks even if, like in some cases, the column of the gas chromatograph is overloaded. 

The best way to avoid mistakes in the identification of poorly separated peaks is to inject a sample of lower concentration. Alternatively, the retention times may also be taken into consideration to confirm the identification. These problems especially affect the evaluation of chromatograms of samples from polytoxicomanes who consume high doses, as in these cases both very small and very large peaks of relevant substances must be identified (e.g. benzodiazepines... 

The possibilities of TLC today can be fully exploited only by using powerful emitters which render possible the evaluation of chromatograms in the short and long wave UV region. The current technical situation demands compromise solutions however. 

Several practical examples of quantitative evaluation of chromatograms, best done by elution before the colour reaction and then subsequent spectrophotometry, are discussed later. Matthews and coworkers [122] have carried out more precise studies of this procedure in comparison with PC and GC and obtained satisfactory results. 

Vovk, I, and Prosek, M. (1997). Quantitative evaluation of chromatograms from totally illuminated thin layer chromatography plates. J. Chromatogr., A 768 329-333. 

In OPLC, the development, the detection and quantitative evaluation of chromatograms may be performed in off-line and on-line mode. The off-line detection and densitometric determination of analyte are performed by the same manner in OPLC as in classical TLC/HPTLC. 

Quantitative evaluation of TLC plates is more complicated than quantitative evaluation of chromatograms in HPLC and gas chromatography (GC). The first and the simplest integration algorithms were developed in GC, because with this method substances are eluted from a column and the gas mobile phase has no evident influence on detectors. In HPLC, the integration procedure is more... 

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