N2 for GC-MS "Rest" Gas

[DReggio]

Restek resells it from Swagelok Restek part #23219 for 1/8" brass $116

It can also be ordered directly from Swagelok cheaper
B-41XS2 $62.10

Awesome thanks!

[LALman]

I did as James suggested and installed the T valves so I could switch back and forth from He to H2 easily. H2 is considerably cheaper than He at ~$175 for a T size of UHP Hydrogen. Locally I have one vendor selling a T UHP He for $327 and the other selling the same size for ~$1100. I was using the latter vendor for most of the rest of my gases. You can guess which vendor I fell back on for He.

I am using dewar LN2 for purge gas and have used it for "Rest" gas. But I went with the hydrogen because I will eventually switch both my GC-MS to H2. Also, I am already using H2 as the carrier for my GC-FID. I've not seen any contamination from the T valves. But I did buy them brand new from the Swagelok dealer instead of half the cost on Amazon because of dubious provenance.

Note: My 5890/5972 can only flow at 0.6mL/min or higher when on hydrogen with a DB-VRX 20m 180um x 1um.

When I was trying H2 for Volatiles I went with a longer column of 40m or 60m to increase the head pressure so I could achieve lower flows of H2. The run is a little longer but not terribly so and with a higher head pressure I had better control of the flow so the retention times were more reproducible. The same works for a semivolatile injection of Methylene Chloride, if you can run a longer column to increase the head pressure you reduce the backflash of the solvent for better peak shapes, and with H2 the run times are no longer than the shorter column using Helium.

RE 40m or 60m column: I will certainly keep that in mind for my next column purchase. I think it might also move the gases away from the water surge I get from the Tekmar3000. That might prolong times between source cleaning and filiment replacement. Even though I am running RT locked there is some movement of the early analyte peaks even at toluene-d8 which is my locking compound.