Retention separation time

If the sample components have a widely varying degree of retention, separation times can be excessively long for reasonable peak resolution. To improve the separation, programming of some variable during the course of the separation is necessary. The most common parameters are flow rate, solvent strength, temperature, and column type. 

The stationary phase is selected to provide the maximum selectivity. Where possible, the retention factor is adjusted (by varying the mobile phase composition, temperature, or pressure) to an optimum value that generally falls between 2 and 10. Resolution is adversely affected when k 2, while product dilution and separation time... 

Again from Figure 1.8 it can be seen that resolution will initially increase rapidly with retention starting at k 0. By the tine k reaches a value of around 5, further increases in retention result in only small changes in resolution. The optimum resolution range for most separations occurs for k between 2 and 10. Higher values of k result in excessive separation time with little concomitant iagnrovement in resolution. 

It is this ordering that gave the concept a theoretical bent as real separations are not ordered the retention times in most separation techniques appear almost random across a range of separation time. The mathematical definition of peak capacity, nc, for an isocratic separation is given as (Grushka, 1970)... 

Total theoretical peak capacity for the ID and 2D LC/MS analyses of the yeast ribosomal protein sample was calculated as 240 and 700, respectively. Individual separation peak capacities were calculated by dividing the total separation time by the average peak width at baseline, and the 2D peak capacity determined as the product of the peak capacity of the two dimensions. These theoretical calculations rely on optimal use of the two-dimensional separation space, which in turn is dependent upon the lack of correlation between the component retention times in the two separation modes. Thus, the maximum use of the theoretical peak capacity is not only dependent on the selection of chromatographic modes based on different physicochemical... 

Effect OF Efficiency, Selectivity, and Retention on Separation Time... 

Similarly, ahigh retention factor also favors high resolution. However, a high retention factor results in increased retention time. The separation time is given as... 

Gas chromatography uses a separation technique to divide the urine extracts into the component parts. An inert gas carries the urine through chromatographic columns, and the samples are separated by their boiling temperature and by their affinity for the column. Compounds are identified by separation time, called retention time. The retention time is unique and reproducible for each drug in a given chromotographic column. 

Centrifugal partition chromatography (CPC) relies on centrifugal force rather than gravitation for the retention of the stationary phase and solvents can be pumped at higher speeds through the instruments. In addition, no need for droplets formation is required. This allows shorter separation times, without loss of resolution, and an infinite choice of solvents with the only requirement of forming two immiscible phases, stable with the time. Chloroform-based systems have been mostly used for the separation of saponins due to their favourable partition coefficient towards such solvents. [116, 119, 120]. 

Efficiency Separation Factor (a) Specificity (Detector) Retention Quantitative Time Reproducibility Reproducibility Sensitivity Linearity Dynamic Range Throughput (Preparative) Speed Baseline Stability Total... 

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