Temperature-programmed separation high-speed

FIGURE 5.24 High-speed temperature-programmed separation of a 20-component pesticide mixture without stop-flow operation (a), with a 2-s-wide stop-flow pulse to separate components 2 and 3 and (c), and with two stop-flow pulses to separate component pairs 2,3 and 10,11. Components are 1, a-BHC 2, P-BHC 3, y-BHC, 4, 8-BHC 5, heptachlor 6, aldrin 7, heptachlor epoxide 8, a-chlordane 9, y-chlordane 10, 4,4 -DDE 12, dield-rin 13, endrin 14, 4,4 -DDD 15, endosulfan II, 16, 4,4 -DDT 17, endrin aldehyde 18, metoxychlor 19, endosulfan sulfate 20, impurity 21 endrin ketone. 

High-speed separations of wide-boiling-point-range mixtures require fast temperature programming. However, if the programming rate is too high, a serious... 

Figure 4.9 Separations of tangerine oil a) conventional GC temperature programming from 50 to 240°C at 9°C/min b) high-speed GC 50 to 240°C at 60°C/ min.

If readsorption is important part of surface event, its influence on temperature-programmed desorption is that TPD profile broadens towards higher desorption temperatures the same stands for diffusion limitations. Therefore, the task to neglect or minimize the effects of these processes is imposed and it is relatively easy if TPD experiments are performed in UHV setups. The pumping speed should be sufficiently high to prevent readsorption of the desorbed species back onto the surface. However, in the case of flow systems there are many experimental conditions that have to be adjusted even though, the interpretation of data obtained from TPD experiment is not simple—in the estimation of kinetic parameters, those experimental conditions have to be taken into consideration. Therefore, the derivation of kinetic and thermodynamic parameters from the results obtained in UHV and in the flow system will be discussed separately. 

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