Chromatography band broadening

Hydrodynamic (kinetic) aspects of chromatography, band broadening and column efficiency... 

This equation is based on experience with liquid chromatography of low molecular weight samples displaying single peaks. Its application for the GPC of polymers, however, contains a disadvantage, as it mixes two inseparable properties the retention difference for the separation and the peak width for the contrary effect of band broadening. Such a procedure is acceptable if both effects are accessible for an experimental examination. For the GPC experiment, we do not possess polymer standards, consisting of molecules that are truly monodisperse. Therefore, we cannot determine the real peak width necessary for a reliable and reproducible peak resolution R,. This equation then is not qualified for a sufficient characterization of a GPC column. 

Traditionally, column efficiency or plate counts in column chromatography were used to quantify how well a column was performing. This does not tell the entire story for GPC, however, because the ability of a column set to separate peaks is dependent on the molecular weight of the molecules one is trying to separate. We, therefore, chose both column efficiency and a parameter that we simply refer to as D a, where Di is the slope of the relationship between the log of the molecular weight of the narrow molecular weight polystyrene standards and the elution volume, and tris simply the band-broadening parameter (4), i.e., the square root of the peak variance. 

In the chromatography of plant extracts on an enlarged scale, there are a few main problems general elution because of the differentiated polarity of complex mixture components being separated the structural and chemical analogy of compounds and resolution decrease due to band broadening. 

Terabe, S., Otsuka, K., and Ando, T., Band broadening in electrokinetic chromatography with micellar solutions and open-tubular capillaries, Anal. Chem., 61, 251, 1989. 

Injection systems of a capillary gas chromatography should fulfil two essential requirements (i) the injected amount should not overload the column (ii) the width of the injected sample plug should be small compared with band broadening due to the chromatographic separation. Good injection techniques are those which achieve optimum separation efficiency of the column, allow accurate... 

Packed columns, 10 769-772, 773 band broadening, 6 412 for distillzation, 5 768-776 gas chromatography, 6 377, 379 instrumentation, 6 423-424 Packed column supercritical fluid chromatography (pSFC), 19 567 Packed fiber-bed mist eliminators, 23 781 Packed towers, 25 810, 811 Packing(s)... 

The band broadening may be characterised by a plate height, and its causes provide a basis for understanding why modem chromatography is such an efficient separation technique. 

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