TD-GC/MS - Lost of sensitivity

Discussions about GC-MS, LC-MS, LC-FTIR, and other "coupled" analytical techniques.

2 posts Page 1 of 1
Dear all,

I need your help cause I'm trying to solve the problem myself but with any results…

I will try to summarize point by point.

- Thermal Desorber Unity 1 Markes, buy in 2007, no support on this since 2015 in France, no spare parts available. Coupling by direct transfert line to GC (no injector)
- GC Agilent 6890, buy in 2007, full maintenance contract.
- MS Agilent 5975, buy in 2007, full maintenance contract. HED + supply HED change in 2017, diffusion pump change in 2018

All was working good up to last Thusday. We perform the calibration curve (injection of a solution of Toluene in Methanol in Tenax tube) and we see that the reference point is lower (1.8E8 area) in comparison what we have generally (2.1E8 area). So we decide to re-check the point: 1.6E8 area. Next point 1.3E8 and now we are at 1E8... each analysis decrease the sensitivity. We try to analysis a sample analysed last week, very poor sensibility and a lot of peaks are missing.
The tune of the MS is very good: H2O < 2%, N2 < 1%, O2 <0.6%, EM = 1550, Repeller = 25, peak m/z 69 = 340 000 absolute unit, peak m/z 219 = 350 000 absolute unit, peak m/z 502 = 45 000 absolut unit.

Solution already try:
- On calibration equipement: change of septum, change of syringe
- On GC: change of column, change of transfer line
- On MS: source cleaning, change of filament
- On TD: change of all seals, change of cold trap, change of thermo desorption tube, check the temperature of thermo desorption oven, check flow rate on split and desorption flow
- On all: check leak

I have no other idea. I think the problem comes from the TD cause GC/MS seems in order (TD seems also in order). SO I'm looking to buy a new one TD but if you have any idea to help me...

Thanks in advance for your help.
I had the same problem a few months ago.
I use am TD/GCMS from Perkinelmer but i think the it's look similar.

The Vaccum and the mass spectrometer tuning condition was also ok.
The Toluene signal became less and less over time.
=>The capillary column between GC and MS was broken in the nut (screw) but still held in place.
At low oven temperature (<100°C) the signal was low due to the leak, but normal at higher oven temperature (no more leak)

maybe you have a similar problem

2 posts Page 1 of 1

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