What would be the effect of increasing the carrier gas flow rate, raising the column temperature, retention?

What would be the effect of increasing the carrier gas flow rate, raising the column temperature, have on the retention time?





Can anyone help me with this chem question?|||In GC a low temp %26lt;180 degrees will cause good separation in early eluting components but may result in longer retention times and band broadening in components (bound to stat phase) which take longer in the column.





At a higher temperature e.g at 250 degrees the solutes which are retained in the stat phase are now eluted faster with the mobile phase thus lower retention times. the first eluted peaks are also eluted faster. Thus peaks formed will be very close to each other resulting in poor resolution.





Thus both high and low temps are problematic.





The solution is to use temperature programming.


i.e start at 150 degree (to elute first peaks) and than increase to 250 degrees to elute longer retained components. This result in good peak separation ie good resolution and no band broadening....





By altering the carrier gas flow rate one is affecting the b and c terms of van deemter equation....By increasing the flow rate one is reducing the band broadening caused by molecular diffusion since there is less time for backward or longitudinal diffusion. Therefore use highest flow rate possible within limits imposed by the c term since by increasing flow rate, analyte in mob phase will move ahead of analyte retained in the stat phase resulting in band broadening. Thus reduce the flow rate within values imposed by the b term(resistance to mass transfer).





Hope this will help you!