Chromatography Forum

how does retention time change from 30m to 60 m long DB5 column? I usually use solvent delay of 5 minute in the 30 m long column. What should be the corresponding solvent delay in 60 m long. Can we relate with the K value only? I used twice the time and 1.5X the column flow but did not work. Does anyone know what should be the proper setting? posting.php?mode=post&f=2#

Why don't you just re-check the solvent retentio time? Way I used to do this was to use an empty vial and with the autosampler wash solution the same as your analysis solution. You get a small wash solvent carryover peak, small enough for the MS to handle, and you can then set your solvent delay accordingly.

Depending on what you are doing, you do not need to worry about when the solvent elutes, simply turn the filament on before the first peak of interest elutes.

Peter

if you translate your present method to a longer column the right way, you will have exactly double the retention time. In order to get the same chromatography, you need to adjust your oven temperature program also, so you get the same elution temperatures.
The average linear gas velocity should stay the same. For this you need probably to double the inlet pressure. solvent delay time should also be twice as long.

Concerning your program conditions, roughly iso times must be doubled and program rates must be Halved.


Jaap de Zeeuw, Restek corporation

Thank you all for valuable comments.