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The van Deemter equation is a hyperbolic function that predicts that there is an optimum velocity at which there will be the minimum variance per unit column length and, thence, a maximum efficiency. The van Deemter equation was the result of the first application of rate theory to the chromatography elution process.
The Purnell equation is an equation used in analytical chemistry to calculate the resolution R s between two peaks in a chromatogram. [1] [2]= (′ + ′) where R s is the resolution between the two peaks
Chromatographic peak resolution is given by = + where t R is the retention time and w b is the peak width at baseline. The bigger the time-difference and/or the smaller the bandwidths, the better the resolution of the compounds. Here compound 1 elutes before compound 2.
The valley definition defines ΔM as the closest spacing of two peaks of equal intensity with the valley (lowest value of signal) between them less than a specified fraction of the peak height. Typical values are 10% or 50%. The value obtained from a 5% peak width is roughly equivalent to a 10% valley. [1]
The [N 1/2 /4] term is the column factor, the [(α-1)/α] term is the thermodynamic factor, and the [k 2 '/(1+k 2 ')] term is the retention factor. The 3 factors are not completely independent, but they are very close, and can be treated as such.
where is the number of theoretical plates (also called the "plate count"), H is the total bed height and HETP is the height equivalent to a theoretical plate. The material in packed beds can either be random dumped packing (1-3" wide) such as Raschig rings or structured sheet metal .
Full width at half maximum. In a distribution, full width at half maximum (FWHM) is the difference between the two values of the independent variable at which the dependent variable is equal to half of its maximum value.
, the carbon number of n-alkane peak heading peak i, the retention time of compound i, minutes, the air peak, void time in average velocity = /, minutes; The Kovats index also applies to packed columns with an equivalent equation: