Claire--

I've had occassion problems where just saving the tune settings would
cause them to shift slightly and cause a large drop in intensity.  I try
to adjust the tune settings to a more robust region, albeit sacrificing
some intensity.  You can double check your settings after tuning and
then again during a run to make sure there are no changes on passing
them to the current gas configuration.  You may also want to double
check the peak centering routine--the hvdac values for tuning and after
peak centering during the GC run should be the close to each other.  If
they are a bit off, or the peak centering looks funny, you may have to
redo your mass calibration.

good luck

take care

gerry

C Bickers wrote:

> Dear All,
>
> I am currently working on a ThermoFinnigan Delta XP coupled via a GCIII
> interface to a Trace GC , with ISODAT 2.0.  After tuning cup 3, with
> reference gas CO2, I can achieve a signal intensity of ~7700 mV for
> m/z 45.
> After the injection of a standard, or even after carrying out a
> diagnostic
> test, the intensity drops by an order of magnitude.  After tuning cup 3
> once more, it easily returns to ~7700 mV signal, but again drops to
> ~700 mV
> when the system is operated.
>
> Has anyone experienced any problems like this and can offer any help?
>
> Thanks,
> Claire
>
> ----------------------
>
> Claire Bickers
> Organic Geochemistry Unit
> Biogeochemistry Research Centre
> School of Chemistry
> University of Bristol
> Cantock's Close
> Bristol
> BS8 1TS
> UK
>
> Tel: +44 (0)117 3316795
> [log in to unmask]
>