Chromatography Forum

Hi!

I can't figure out really what is happening here. The air/water check RIC was always 5,000-9,000 but all of a sudden it changed to ~44,000 RIC. Even though the check passes, I am confused. I have checked for leaks, changed the liner, septum, cut off front of column, bakeout column and bakeout trap... but all this to no avail (did these all one at a time, of course).

I did notice that when I cut off the front of the column, I watched the air/water check as the temp rose and it looked normal until the injector reached ~170. After that point the RIC rose to ~44,000......

Any ideas??

The column installed right now is a VF-5ms. The analysis I am preparing for is PAHs in cyclohexane (standards only). The RTs haven't changed at all, just the RIC of the air/water...

cheers!
Kerri

Maybe the elevated temperature of the injector causes a temporary leak.
Did you tighten the injector nut while is was warmer than 50°C? If you did so, let the injector cool down and use a new septum.
Did you also check that the ferrule of the column nut is tight?
Maybe some sample residue is creeping out from the gas or split line from previous overfilling of the injector?
Manually check for the ions of the leak.

I'd spray all injector parts with argon to check for that leak (note: argon needs the dead time of the column from the injector to the detector).

Let us know what you find

Well, i didn't find any leaks int he injector.

Then I just decided to do a full tune. I'm glad I did because there were a lot of things that were terribly bad. RF was way too high, cal gas was basically all the way open, and because of that the EMT voltage was set at 2300 V. After the tuning, the EMT went to 2150 V and the RIC of the air/water check went to ~23,000.

I called the engineer and he said that as the EMT ages and we have to use a higher voltage, and with that we will typically see higher RIC in the air/water checks.

Interesting.

So. Back to normal (I guess?).

Thanks!!!!
Kerri