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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.
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.
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
It is simply a hypothetical equilibrium stage. However, the theoretical plate in packed beds, chromatography and other applications is defined as having a height. The empirical formula known as Van Winkle's Correlation can be used to predict the Murphree plate efficiency for distillation columns separating binary systems. [4]
A high value for resolution corresponding to good separation of peaks is similar to the convention used with chromatography separations, [13] although it is important to note that the definitions are not the same. [14] High resolution indicating better peak separation is also used in ion mobility spectrometry. [15]
, 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:
The definition of peak capacity in chromatography is the number of peaks that can be separated within a retention window for a specific pre-defined resolution factor, usually ~1. It could also be envisioned as the runtime measured in number of peaks' average widths. The equation is shown in the Figure of the performance criteria.
The Scherrer equation, in X-ray diffraction and crystallography, is a formula that relates the size of sub-micrometre crystallites in a solid to the broadening of a peak in a diffraction pattern. It is often referred to, incorrectly, as a formula for particle size measurement or analysis.