Chromatography Forum

Hi all
I have recently retuned my MS (HP-5973).
The method I am working to requires a DFTPP peak area of 750000 - 1250000 with a 1ul injection of DFTPP @ 50 ug/ml hence my peak areas are usually fairly stable.

Following retuning i adjusted the EM voltage to get the appropriate peak area (962297).

The following run (a calibration) my IS areas were highly erratic and my 1st tune the next day had a DFTPP area of 650000 (approx)

I have not experienced this problem when changing the EM voltage by small incriments however this is the second time i have seen it following a retune.

Does the electron multiplier take a while to "settle" following a tune or following a significant change in EM voltage?
Thanks for your time. AW

Diffusion pump or turbo pump? Was the source vented before tuning and if so how long was it allowed to stabilize before first tuning?

I have seen changes like that if you tune too soon after venting where the system doesn't have time to fully equilibrate thermally.

Source was vented to install a new filament however the system was left overnight to stabilise.
Next morning there was a leak at the side plate so vented, sorted that and pumped down again. Checked seal on the side plate in the afternoon and left overnight again.
Air and water check the next morning was slightly high for water (about 13%) however following a half hour bake out of the column it had returned to normal (<5%). Peak areas look to have stabilised now and air and water both <1% but will get the turbo/diffusion pumps checked (anual service coming up next week)

Cheers
AW