Chromatography theoretical considerations

Y Xu, PA Siegenthaler. Phosphatidylglycerol molecular species of photosynthetic membranes analyzed by high performance liquid chromatography theoretical considerations. Lipids 31 223-229, 1996. 

Jandera, P. Churacek, J. Gradient elution in liquid chromatography II. Retention characteristics (retention volume, bandwidth, resolution, plate number) in solvent-programmed chromatography—Theoretical considerations. J. Chromatogr. 1974, 91, 223-235. 

Jandera, P. and Churacek, J., Gradient elution in liquid chromatography. I. The influence of the composition of the mobile phase on the capacity ratio (retention volume, band width, and resolution) in isocratic elution — theoretical considerations, /. Chromatogr., 91, 207, 1974. 

Docherty, G., Jones, V. and Evershed, R. P. (2001) Practical and theoretical considerations in the gas chromatography/combustion/isotope ratio mass spectrometry 813C analysis of small polyfunctional compounds. Rapid Communications in Mass Spectrometry 15, 730 738. 

Colin, H. and Guiochon, G, Comparison of some packings for reversed phase high performance hquid sohd chromatography, ii. Some theoretical considerations, J. Chromatogr., 158, 183, 1978. 

The Van Deemter equation can be applied to gas chromatography with a different emphasis on the relative importance of its terms. In fact, the interactions between an analyte and a stationary phase are much simpler in gas chromatography than those in liquid chromatography since the mobile phase does not modify the stationary phase in any way. The theoretical considerations are different for packed GC columns vs open tubular capillary columns. 

Boehm, R. E., Martire, D. E., and Armstrong, D. W., Theoretical considerations concerning the separation of enantiomeric solutes by liquid chromatography. Anal. Chem., 60, 522-528,1988. 

Theoretical considerations indicate that, on homogeneous surfaces, C. is smaller than Cj/, and this implies highly efficient applications of gas-solid chromatography. 

The ELS detector was previously also referred to as a mass detector, pointing to the fact that the response is (mainly) determined by the mass of the sample rather than by its chemical structure. Van der Meeren et al., though, demonstrated that the ELSD calibration curves of phospholipid classes were also dependent on the fatty acid composition (52). The dependence on the fatty acid composition is, however, completely different in nature and much less pronounced than for UV detection. The reason for this behavior is to be found in the partial resolution of molecular species, even during normal-phase chromatography. Thus, the peak shape depends not only on the chromatographic system but also on the fatty acid composition and molecular species distribution of the PL sample (47). Because it was shown before, based on both theoretical considerations and practical experiments, that the ELS detector response is generally inversely proportional to peak width (62,104), it follows that the molecular species distribution of the PL standards used should be similar to the sample components to be quantified. It was shown that up to 20% error may be induced if an inappropriate standard is used (52). 

For both GC and LC, the efficiency of a chromatographic system is optimal at intermediate flow velocities. Optimal performance is usually not obtained in practice because of the emphasis on separation speed, which requires the use of greater than optimal flow rates. Theoretical considerations of the thermodynamic and kinetic aspects of chromatography led to the development of HPLC and capfllary GC, both of which possess the speed necessary for clinical analyses. 

Theoretical Considerations in Electrokinetic Separations. Models have been proposed for electrophoretic (52) and electrochromatographic systems. Similar to developments in chromatography, we may write a model equation for these systems ... 

When describing the chromatographic process in terms of mathematics it is necessary to define a suitable (sufficiently realistic and yet mathematically tractable) model of chromatography. From the point of view of theoretical considerations the following models are of interest [10],... 

Theoretical considerations are a useful guide to the practical design and operation of the chromatographic experiment. The object of chromatography is separation— or rather, separation in a reasonable time. 

Knox JH, Grant IH. (1987). Miniaturization in pressure and electroendosmotically driven liquid-chromatography— some theoretical considerations. Chromatographia 24 135-143. 

Many of the applications within forensic science adopt a reverse phase (RP) HPLC mode of separation in relation to analyses. We have chosen to use example applications of HPLC based on this particular mode of chromatography because it is the most frequently used. We have broken each chapter down into theoretical considerations with examples where appropriate, a key point summary, a series of questions where appropriate, and, finally, a list of books and journal articles that we believe will give further, thorough insight into each of the topics covered. We have attempted to keep the book as succinct as possible whilst still providing sufficient information to allow the reader to develop his or her knowledge at an effective pace. 

An absolute method of measuring the molecular weight is one that depends solely on theoretical considerations, counting molecules and their weight directly. The relative methods require calibration based on an absolute method and include intrinsic viscosity and gel permeation chromatography (GPC). 

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