Gradient chromatography principles

The most important techniques of the chromatography principle are column elution based on a solvent — non solvent gradient, and column elution with a superimposed temperature gradient. 

Diffusion coefficient. Dm. Coefficient characterizing the intensity of the diffusive flux or the rate of diffusion along a concentration gradient. In principle, the diffusion coefficient is a function of the concentration, and the diffusive flux of one component depends on the concentrations of all the components of the system. These effects are neglected here, since only dilute solutions are used in chromatography. For the same reason, diffusion coefficients at infinite dilution are used. 

Principles and Characteristics SFC-MS is a sensitive coupled technique that can be selective or universal it was first mentioned in 1978 [396]. Further developments are given in Table 7.36. It is used in an on-line mode with open cell gas-phase interfaces, where the mobile phase is decompressed to low pressures. SFC presents a number of features which allow for easier coupling with MS than other chromatographies. In practice, however, SFC-MS coupling did not turn out to be as easy as expected, a fact which can be ascribed to the problems met in the adiabatic expansion of the mobile phase and the effects of pressure gradients in the ion... 

This chapter reviews the underlying principles of ion chromatography and its application in pharmaceutical analysis. It provides an overview of eluent systems, applications of gradients, electrolytic eluent generation, suppressors, and stationary phases. Applications of ion chromatography to the confirmation of counter ions, active ingredient analysis, competitive analysis and development work are discussed. 

Isocratic versus Gradient Elution. The principles of chromatography just described hold true for isocratic elution schemes, in which the nature of the mobile phase remains constant throughout the de-... 

A relatively new analytical separation technique known as Ultra Performance HPLC or Ultra Performance Liquid Chromatography (UPLC ) is similar in principle to HPLC except that it uses smaller particle sizes (<2.5 pm) and higher flow rates to increase the speed of separation and peak capacity, or number of peaks resolved per unit time in gradient separations (Swartz, 2005). UPLC was used to separate and quantify six major polyphenolic compounds in cocoa with a 50 mm by 2.1 mm column with a 1.7 pm particles size and a run time of only... 

In the isothermal chromatography (IC) experiments, one usually measures elution curves - the time-dependent relative concentration of each of the analytes in carrier gas at the column exit. In principle, one could also fix the internal chromatogram (e.g., by rapid cooling of the column well below the working temperature) actually, it is impractical except for the compounds of similar volatility. In the ther-mochromatographic (TC) separations of mixtures of differently volatile tracers, given a proper stationary temperature profile, each of the components finally comes to practical rest somewhere within the column. The temperature gradient g may... 

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