Chromatography Forum

Hi,

This is my first time posting here but I've noticed that the forums are quite useful

So recently we moved the GCMS from one laboratory to another and in doing so have made our MS unhappy.
After first moving the MS, I've tried tuning and it seemed fine (EM sitting about 1600 and Repeller at 32).
However, the next day when I came in to run a sample, the trace showed no baseline and only a few scattered peaks of arbitrary size. So I figured it needed re-tuned, but the tuning now fails stating that the peak widths are inconsistent.
I moved the column slightly, for fear that I'd inserted it too far into the EI source and this seemed to allow me to tune again and subsequently run samples but now today I'm having the same problem with scattered sharp peaks, no baseline and tuning failures.

Any advice?

K

Does the instrument have a turbo or diffusion pump?

Turbo.

How's your air/H2O? Make sure your pump connections are good and your carrier gas connections aren't leaking.

bad filament?
broken repeller insulator?

how's your vacuum. E-5? range
check for leaks

When moving the instrument, I disconnected the MS from the GC. After reconnecting, the gases (N2, O2, CO2) were all quite high (around 20%) but letting the instrument equilibrate has lowered all of these below 2%.
The Air/H2O is higher than the others, last time I checked it was around 100%.

The instrument is able to vent and pump down without problems. The pump routinely sits >90%.

I'm not sure how you check the filament, repeller instrument for damage?

The filament usually you just switch to the other one. Go to manual tune and if it says filament 1 switch it to 2 or vice versa. Chances are both aren't bad.

As for the repeller insulator you need to vent the system and take apart the source. There are two cylindrical hollow white insulators on the repeller one on each side of the heater sensor array. Check to see if they are intact.

You seem to have a leak if your air/H2O is that high. I wouldn't switch to the opposite filament until you correct the air leak. High air/H2O will damage filaments (bowing and possibly blowing them). MSCHemist is right. The filament you are using may be damaged, the one you haven't been using is probably good so you don't want to damage that one. Once you correct the air leak you can try tuning on the filament you''ve been using and then tuning on the opposite filament and choose the one that gives you the best tune. If you still have problems on both filaments, I would then remove the source and make sure it's clean and the insulators aren't dirty or cracked.

Yep but the first order of business is to hunt down any leaks. If you have an electronic leak detector go arround with that. Otherwise make a bottle of 50% isopropanol in water and put some in each gas line connection between the tube and nut and watch for bubbling. If you see any try tightening it and if that doesn't stop it cut it off and put a new nut ferrule set on.

for inside the oven spray and arround the gc compressed air at the connections while scanning in manual tune mode for m/z 52 from the propellant. If a leak is present where you sprayed it should show up instantly as a 52 peak and quickly subside.

Could be a funky tune. Try another ( Stune or DFTTP tune).

Thanks for your input. I'll give these ideas a try, and let you know.

The exact values from my most recent successful tune are:

Emission - 34.6
EIEnergy - 69.9
Repeller - 34.31
EMVolts - 1529

H2O - 1.72%
N2 - 1.84%
O2 - 0.45%
CO2 - 0.25%
N2/H2O - 106.85%

Also, I've tried other tune files and had no luck, the tune still fails. I've even tried loading up an old atune file that worked in the past but this fails too.

Loose connections somewhere? If the connections to the source are loose strange things could happen. The source connections should be snug enough that they don't come off with a gentle pull using forceps. If loose you can try gently squeezing them with needle nose pliers. GENTLY.

I will assume you checked that the PFTBA valve is in fact "open" when doing a manual tune? This sounds exactly like something I experienced and for whatever reason the software had defaulted to a closed valve. Also make sure there is in fact PFTBA in the little glass bulb. One of my 5975s is about to run dry. Other than that and leak checking..maybe rebuild the source. Very possible it's a loose connection somewhere..as suggested.