Chromatographic terms

Two different components are separated in a chromatographic column only if they spend different amounts of time in or at the stationary phase. The time in which the components do not travel along the column is called the solute retention time, ts-The column dead time, tm, is defined as the time necessary for a nonretained component to pass through the column. The gross retention time, t, is calculated from the solute retention time and the column dead time, as shown in Eq. (2.1)  

The pealc height at any given position x can be derived from Eq. (2.2)  

Handbook of Ion Chromatography, Fourth Edition. Joachim Weiss. 

Peak height at maximum Any particular point within the peak Position of peak maximum 

Peak width at the baseline as determined by the intersection points of the tangents drawn to the peak above its points of inflection 

Since ion chromatography is really a form of column liquid chromatography, it follows that the same chromatographic terms should be used. The major terms are summarized in Fig. 5.1 and Table 5.1. The picture is unfortunately clouded by the fact that not everyone uses the same name or exactly the same symbol for some of these terms. For example, it is now recommended to use the name retention factor for what was called the capacity factor for many years. Both k and k have been used as the symbol 

Retention time ror/R Time to elute a peak to its maximum concentration 

Dead time / or tM Time to elute a non-sorbed marker 

Height equivalent of a theoretical plate H H = UN (f, = column length) 

A better way to look at chromatographic efficiency is to consider the dynamic processes that contribute to peak broadening. Recall that chromatographic peaks are Gaussian and that the width of a peak at its base is approximately four standard deviations w = 4(7. The factors that contribute to peak broadening are additive provided the variance (a ) is used instead of the standard deviation. The total variance (ff tot) is the sum of variances due to multipaths (cT mp). axial diffusion (u dif). resistance to mass transfer (ff mt) and extra-column ( r ec)- 

Ion Chromatoff apky, 4 Ed. James S. Fritz and Douglas T. Gjerde Copyright 2009 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ISBN 978 3-527-32052-3 

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Before proceeding to a more detailed discussion of LC apparatus or separation technology, it is necessary to define some chromatographic terms and, in particular, the properties of a chromatogram that will be... 

So far the models proposed to explain retention in RPC have largely remained the province of the physical chemist. The mathematical difficulty of using these models and their lack of a simple conceptual picture of the retention process in familiar chromatographic terms has diminished Interest in their use compared to simple empirical rules for trial and error optimization of separations. 

It is evident that the chromatographic term is the only source for enantioselecti vity because the retention factors may differ for the distinct enantiomers, while electrophoretic mobilities are identical for enantiomeric species. In other words, electrophoretic mobilities, like Veo, are nonselective contributions in view of generating chiral separations, but may positively contribute to the selectivity between distinct compounds (such as, for example, chemical impurities) but also of diastereomeric species. 

In chromatographic terms the purpose of this paper is to find a mixture composition which results in a good separation of the solutes, both under standard environmental conditions and for different temperatures and relative humidities. In this section this chromatographic purpose is combined with the Taguchi approach to robustness. This results in mathematical expressions which quantify the separation and the robustness against environmental influences. 

G. R. Asbury and H. H. Hill, Jr., Evaluation of Ultrahigh Resolution Ion Mobility Spectrometry as an Analytical Separation Device in Chromatographic Terms, J. Microcolumn Sep. 2000,12, 172 H. E. Revercomb and E. A. Mason, Theory of Plasma Chromatography/Gaseous Electrophoresis, Anal. Chem 1975,47,970. 

As mentioned above, the basic principle of NLC is the same as for conventional techniques. The separation is identified and characterized by measuring retention times, capacity, separation, and resolution factors. Therefore, it is necessary to explain the chromatographic terms and symbols by which the chromatographic speciation can be understood and explained. Some of the important terms and equations of the chromatographic separations are discussed below. The chromatographic separations are characterized by retention (k), separation (a), and resolution factors (Rs). The values of these parameters can be calculated by the following standard equations [92]. 

Figure 1.6 Chromatographic terms used to calculate column capacity.

The chromatograph is built around the column, in which the actual separation takes place. The column accommodates the two chromatographic phases the stationary phase, which remains in the column, and the mobile phase, which is transported through it. Separation is achieved because different sample components (solutes) show different distributions over the two phases. A solute, having such a high affinity towards the stationary phase that it resides in this phase exclusively, will stay in the column indefinitely. A solute, that does not enter the stationary phase at all, will be transported through the column at the same speed at which the mobile phase is transported. In chromatographic terms, the latter is called an unretained solute. 

Over time, the instrument has been used more widely by chromatographers, and the Analyst software is a response to this as the operation of the application is simpler and uses chromatographic terms more than mass spectrometry ones. This difference in design philosophy is a complicating factor for the data migration as terms have to be mapped between the applications, which we will describe later in this chapter. 

One further goal of this chapter is the harmonization of general chromatographic terms between engineers and chemists, avoiding slang terms" that are quite common in the literature and daily use. 

All these parameters depend on the mass loadability of the column and change significantly when a critical loadability is reached. The critical mass loadability of analytical columns is usually reached at a 10% reduction of the retention coefficient or at 50 % decrease of column plate number. At higher values the column is, in chromatographic terms, overloaded. 

The chromatographic terms for the characterization of a separator column can be inferred from Fig. 2-1. 

Some important chromatographic terms are explained below and illustrated by a schematic diagram based on a diagram by Geiss [4] (Fig. 57) ... 

Appendix 1 Glossary of chromatographic terms Appendix 2 Table of chromatography symbols Index... 

A glossary of chromatographic terms and a table of chromatographic symbols are included in the appendices at the end of this book. Further information on the terminology of chromatography is available in the literature [8]. 

The 5th edition also includes an updated and expanded set of model experiments which reflect the current practice of chromatography. These are supported by a new chapter of a comprehensive set of problems with answers. A further new feature is a glossary of chromatographic terms and a list of symbols as an aide-memoire and to support the preceding chapters. 

The cavity model of solvation provides the basis for a number of additional models used to explain retention in reversed-phase chromatography. The main approaches are represented by solvophobic theory [282-286] and lattice theories based on statistical thermodynamics [287-291]. To a lesser extent classical thermodynamics combining partition and displacement models [292] and the phenomenological model of solvent effects [293] have also been used. Compared with the solvation parameter model all these models are mathematically complex, and often require the input of system variables that are either unknown or difficult to calculate, particularly for polar compounds. For this reason, and because of a failure to provide a simple conceptual picture of the retention process in familiar chromatographic terms, these models have largely remained the province of the physical chemist. 

Asbury, R.G. Hill, H.H., Jr., Evaluation of ultrahigh resolution ion mobility spectrometry as an analytical separation device in chromatographic terms, J. Micwcol. Sep. 2000, 12(3), 172-178. 

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