Optimization of Carrier Gas Flow

The aim of flow optimization for given column properties at a given temperature and with a given carrier gas is to find the flow rate which gives either the maximum number of separation steps or at adequate efficiency the shortest possible analysis time. 

The HETP and the number of theoretical plates N depends on the flow rate of the mobile phase v according to van Deemter. The linear flow rate v of the mobile phase is calculated from the chromatogram  

Incomplete partition equilibrium. The transfer of analyte between the stationary and mobile phases only has a finite rate relative to that of the mobile phase, corresponding to the diffusion rates. The contribution to peak broadening increases with increasing flow rate of the mobile phase. 

In particular, in GC X GC, the flow rate of the second short column is accepted to be significantly above the ideal flow rate using the direct connection to the modulator. A split device would be needed between the modulator and second column for the independent adjustment of the flow rate. Most GC x GC applications do not use a flow adjustment for the second column because of the cut in substance concentration and hence sensitivity of the method. This is probably the most important factor, the overwhelming increase in peak separation and S/N by using a high-flow compromise. 

K is also expressed as the product of the capacity ratio Id) and the phase ratio (/ ). 

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