Chromatography Forum

Setting up a method with a DB-1 30m x 530um x 1.5 set flow to 36cm/sec should give 3.7psi and about 4.7ml/ml. When I set the split to 100:1 (split flow about 470ml/min) the column pressure moves to 4.1psi and the instrument won't go ready.
If I decrease the split to 75:1 column pressure returns to 3.7psi and run can start.
Do you think there is some built up restriction in the split vent causing back pressure. Or is the split flow just too high?

Yes, as the split flow gets higher the flow restrictions in the plumbing will become too great to offset. I have heard claims from Agilent that the inlet seal with a cross (rather than a single line) is needed for large split flows. I haver never tried it; better to use a low enough flow. Just keep in mind that some portion of the pressure reading is due to plumbing restrictions.

I routinely run 500:1 splits for pure materials checks with a standard 30m .25um .25mm column and have no issues using a standard gold seal. Perhaps check that you split line is not gummed up. A lot of crap condenses in those lines from the inlet as it not heated. I checked mine for the first time a year ago and it was full of very foul black tar.