[tozlj525]

this is thermo Delta v Isotope ratio mass spectrometry. Last week, we replaced a new filament of ion source. Now there is no peak center of any gas: CO2, N2, H2O, and the backgruond is very small, 0.80 mv, should be 40 mv.
all parameters of software are normal.
the high voltage of filament is 3 kv, the box of filament is 0.8 mA, the trap of filament is 0.62 mA. the vaccum is 8.1 e -7.
the High voltage of magnet is 3.0 kv
Does anybody use the same instrument or meet similar problems? Could you give me some tips? thank you very much.

[MOTOBALL]

Dear tozlj525,

I am not familiar with this particular instrument, however some general thoughts for an EI source would be,

(1) is the multiplier ON (or dead or dying) ??

(2) does the electron beam from the filament pass through a small aperture to intersect the sample cloud, and is the aperture blocked /misaligned ??; is there a repeller behind the filament ?? is the filament touching the repeller ??

(3) is the filament misaligned  ??

(4) even if correctly aligned, filaments have been known to sag and therefore fall below the aperture.

(5) is the trap clean  ??

(6) if the multiplier is OK, suggest that you remove source and first give it a VERY careful visual inspection.  Then use a multimeter to make sure that (a) the filament is continuous from post to post, (b) there are no short circuits.

Loss of sensitivity usually comes down to a source contamination issue or an incorrectly assembled source, as referred to above.

You may also have a power-supply board issue, which is beyond my skill-set.

Good luck with this---and please let us know the outcome.

Motoball

[tozlj525]

Dear Motoball,
thank you very much for your reply.
I will keep on reporting what is going on untill the problem is solved.