Chromatography Forum

What is the typical difference in vacuum between isolated MSD vs. MSD connected to GC/MS?
When I block the transfer line I am getting very good vacuum 6x10-7 When I connect the column, I am only getting 4x10-5 with He set at 2PSI. No apparent leaks when looking at the spectrum (14, 28, 18, 32 are all very low compared to helium). It bothers me cause the sensitivity is very low so it doesn’t even tune sometimes. This is Perkin Elmer Clarus instrument, unlike chemstaiton I do not believe there is a way to do full scan or air/water scan.

Those pressure differences sound correct to me, assuming the Clarius pumps are what comparable to a low end Agilent GC/MS.

Some MS will have greater pumping capacity (multiple pumps, etc), but the entry level ones I am used to will read in that range with a 1 mL/min carrier flow.