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In liquid chromatography, the mobile phase velocity is taken as the exit velocity, that is, the ratio of the flow rate in ml/second to the cross-sectional area of the ‘column-exit flow path.’ For a packed column, the cross-sectional area of the column exit flow path is usually taken as 0.6 times the cross-sectional area of the column.
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 second separation is rapid, allowing the introduction of subsequent fractions from the first column without mutual interference. Dallüge et al. [28] reviewed the principles, advantages and main characteristics of this technique. One of the main advantages is the very high separation power, making the technique ideal for unravelling the ...
This also increases the peak height (the peak looks "sharper"), which is important in trace analysis. The gradient program may include sudden "step" increases in the percentage of the organic component, or different slopes at different times – all according to the desire for optimum separation in minimum time.
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]
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 .
A sample whose compounds concentrations are known is used to calibrate the TCD: concentrations are affected to peak areas through a calibration curve. The TCD is a good general purpose detector for initial investigations with an unknown sample compared to the FID that will react only to combustible compounds (Ex: hydrocarbons). Moreover, the ...
Between each sample reading, the mobile phase and filter paper are changed to ensure the best outcomes. The spot capacity (analogous to peak capacity in HPLC) can be increased by developing the plate with two different solvents, using two-dimensional chromatography. [8] The procedure begins with development of a sample loaded plate with first ...