Optimization faster separation

Figure 2.2—Optimum linear velocity and viscosity of carrier gas. The optimal mean linear velocities of the various carrier gases are dependent on the diameter of the column. The use of hydrogen as a carrier gas allows a faster separation than the use of helium while giving some flexibility in terms of the flow rate (which can be calculated or measured). This is why the temperature program mode is used. The significant increase in viscosity with temperature can be seen for gases. In addition, the sensitivity of detection depends on the type of carrier gas used.

Many chromatographic systems are run at or above the optimum flow velocity vopt to achieve faster separation. In this case Eq. 12.57 is no longer valid for plate height. However, for purposes of the present discussion, in which we are seeking ways to reduce plate height but not time, we will assume that the first step, velocity optimization, has been taken, and that Eq. 12.57 is applicable. 

CE versus LC versus CEC. CE will provide for faster separations, while LC will provide for increased sample loading capacity. Complex interactions between the sample, the stationary phase, and the mobile phase can result in a difficult optimization process of CEC-MS methods. LC and CEC do not necessitate high buffer concentrations, thus the ESI signal is not suppressed during analysis. The higher the efficiency of either separation method, the more intense the analyte peaks will be, the better the detection limits, and the more complex samples can be analyzed. 

Optimized conditions allow faster separations (threefold reduction), substantial increased injection volume capacity, reduced degradation of thermally labile compounds, and lower detection limits due to increased sample loadability. 

Flow Rate The optimal flow rate is often chosen based on a best balance between separation speed and efficiency. For a typical 2.1 mm diameter column, the recommended flow rate is 0.2 mL/min. However, it is often advantageous to use higher flow rates than this for faster separation and better peak shape. Therefore, the typical flow rate seen in current bioanalytical applications for a 2.1 mm diameter column often ranges from 0.4 to 0.6 mli min, under which the minor loss in separation efficiency is well tolerated and compensated by the improved separation speed. 

Figure 8 shows the resolution map describing the response of the system versus pH. Indeed, despite the fact that we had reasonable resolution of all components in our first experiment (pH 2.9), it is clear that a small change in pH (Fig. 8) would result in co-elution of components 3 and 4. pH 2.6 appears to oiler a good solution we can proceed to further optimization, examining for an isocratic and/ or faster separation from here. 

Khan, A.I. (2013) Optimizing GC Parameters for Faster Separations with Conventional Instrumentation, Technical Note 20743, Thermo Fisher Scientific, Runcorn, Cheshire, UK. 

Lesellier et al., [23] stndied variables as modifier percentage, backpressure and temperature in supercritical fluid chromatography to optimize the identification of triterpenoids, therefore, had faster separations, which shows... 

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