Tuesday, July 23, 2019

Theoretical plates in HPLC

In chromatography, a sample is dissolved in the mobile phase, which can be solid, gas or liquid. The mobile phase travels through a stationary phase which is immiscible and immobile. Phases are selected such that the analytes of the sample have dissimilar solubility in each phase. A molecule that takes more time to travel than the molecule which is not highly soluble in the stationary phase, but it is highly soluble in the mobile phase. In the form of this inequality in mobility, sample molecules separate from each other while traveling through a stable phase.
Any chromatographic column doesn’t include any physical plates that can be periodically measured for the efficiency of the column. The plates are produced throughout the elution of molecules through the column and it has information regarding the separation process, primarily the peak dispersion. This is a simply measured quantity utilize to take column properties. The number of theoretical plates is an index that is used to calculate the effectiveness and performance of columns. At a specific retention time, they are an indirect measure of the peak width for a peak. The number of theoretical plates (N) in chromatography can be calculated as N=16(tR /W) 2, where tR= retention time and W= peak width. The Column efficiency is a function of dimensions of the column, system flow rate, solute, and retention time (RT) of the solute. The limit of the theoretical plate (Efficiency) is N > 2000.

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