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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 peak is "well-sampled", so that less than 10% of the area or volume under the peak (area if a 1D Gaussian, volume if a 2D Gaussian) lies outside the measurement region. The width of the peak is much larger than the distance between sample locations (i.e. the detector pixels must be at least 5 times smaller than the Gaussian FWHM).
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]
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 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 retention time is the time from the start of signal detection to the time of the peak height of the Gaussian curve. From the variables in the figure above, the resolution, plate number, and plate height of the column plate model can be calculated using the equations: Resolution (R s): R s = 2(t RB – t RA)/(w B + w A), where: