Chromatography Forum

It's making me crazy...

The unit:
P.E. Clarus 500 gc-ms, DB 5 column, UHP He carrier 1 ml/min, E.I. Detector

The problem:

Changed the column after prolonged downtime. Pumped overnight. Good vacuum. HUGE Nitrogen tune peak. LEAKING?

Re-plumbed the column (new ferrules) , Changed to new colum, new ferrules, changed He gas tanks, changed He gas LOT #'s, Squited Freon ALL OVER the system (no freon masses), re-tuned.... slowly loosing control... about to pick up hammer.

after 3 days

m/z
4 = 39%
18 =17%
28= 100%
32= 19%

Help!

I've never used a Clarus...but what is the %response of your closest tuning ion (69?)?

Might not be the column. Could be inlet, carrier gas supply, gaskets...

Next step; take the column out of the MS, plug the column connection to the transfer line and pump down. Nitrogen and oxygen means there is a leak in the MS. No nitrogen and oxygen probably means a leak in the GC or upstream of it.

HOWEVER a peak at 28, which is usually assigned to nitrogen can also appear in a leak-proof system. There was a thread a few months ago on this, can't recall the details, and I have seen it in our lab. Best guess is that it is something coming off the column. What stationary phase do you have ?

Good luck

Peter

After pumping over the weekend I finally get a respectable He peak. I didn't mention it before, but I did seal off the transfer line with a "no hole" ferule" and got no measuarble air peaks.
But today:

18/69 = 0.2%
28/69 = 0.2%
32/69 = 2.0%
44/69 = 7.5%

I will make a blannk run and see waha gives.

Thanks to all of you.

RS

just a real quick thought, have you checked the level of the calibrant in the vial for the MS, perhaps it is low, hence apparently high "leak" signals.

peggsy