Ge9x volumetrix flow rate
Expressed mathematically,įour chromatograms are presented in Figure 4.9. With reference to either a GC or HPLC chromatogram, the resolution, R у is defined as the ratio of the distance between retention times of two separated peaks to the average base peak width, t n, of both peaks, 1 and 2. Our understanding of what causes chromatographic peaks to broaden as they elute has led to the achievement of columns that maximize chromatographic resolution. This measured retention time for acetone, commonly termed the void or dead time, can be used to calculate the linear velocity. In reversed-phase HPLC with ultraviolet absorption detection (RP-HPLC-UV), this author has used as a source of an unretained component the strongly absorbing and water-miscible solvent acetone. Knowing the length of the column, L, enables the linear velocity to be calculated according to In the case of GC, injection of methane or, as this author has done, injection of the butane vapor from a common cigarette lighter using a 10 pL liquid-handling glass syringe gives t 0. Linear flow rates can also be determined independently of Equation (4.26) by measuring the retention time of an unretained component of the injected sample. It then becomes evident that open tubular columns exhibit linear flow rates that are three to five times higher than packed columns, despite the fact that the user would have to replace compressed gas tanks less frequently. The columns are listed from the smallest commercially available diameter to the largest, along with a representative volumetric flow rate passing through the column. Equation (4.26) is used to calculate и for the five most commonly used GC column diameters, and these results are shown in Table 4.4. 18) 26įigure 4.8 reveals that with respect to the average linear velocity, the optimum linear velocity for a packed GC column is lower than that for an open tubular or capillary GC column. Jennings has articulated an interesting relationship between linear and volumetric flow rates, F, incorporating the column radius, r c according to: (p. Any comparison of van Deemter curves, such as that shown in Figure 4.8, must use linear velocity because the influence of the column radius is eliminated. It is the linear velocity that conducts analytes of interest through a chromatographicĬolumn to the detector. Notice that Equation (4.25) examines column efficiency as a complex function of linear mobile- phase velocity.