For fun: GC-MS/MS problem diagnosis

[yangz00g]

What could cause this? A lemon instrument?

Machine: Thermo Trace GC-TSQ Quantum GC triple quadpole MS (< one year old), source: positive EI, source temperature at 250C.

Column: Zebron ZB-Multiresidue (oven program starts at 120C and end at 300C), age of a few month with a few hundred injections.

The instrument's reproducibility appears to vary day to day. For example, %RSD of 10 replicates was 5% on one day and on the following day, without any parameter change, the % RSD was 60%. On some day, a steady decline of IS could be seen on 10 replicates with last one at 50% of the first one (both peak area and high).

Turning: m/z 69 is the base peak on one day and 219 the other day for both Q1 and Q3.

All automatically diagnosis runs passed without parameter problem.

Thanks and have fun.

[Peter Apps]

Try looking at what happens at the other end of the column.

That was fun

Peter

[WK]

I assume you regularly keep the injector/liner clean?
WK

[yangz00g]

More fun here.

Yes, we keep the injector and liner clean, and we have phased out the problem coming from column bleeding, leaking, and contaiminated injector/liner/solvents/carrier gas and unstable oven temperature.

Different Thermo Reps have come and gone, no one could figure out what's wrong. Beacuse this froum has a lot sharp minds, I am here to seek comments.

any other thought? Please continue. Thanks

[Peter Apps]

OK, we need full details of all the instrumental conditions, and what it is that you are analysing, and does the instrument show the same behaviour with other samples. Having to guess is no fun at all

Peter

[haiedc]

What are you analyzing ?

[gpronger]

More than once an inexplicable "Lemon Instrument" was due to what we "water" the instrument with - facility electrical. New industrial construction in the area causing electrical sags; bonded electricians messing up the internal electical of the facility, etc.

Next most common causing inexplicable instrument problems was environmental; weird stuff with HVAC (temp swings). This tended to be more an issue with ICP and ICPMS systems.

Greg

[JI2002]

It seems like a MS problem. The ratios between m/z 69, m/z 131, m/z 131 and m/z 50 should be consistent from day to day, the intensity of the base peak should be consistent too, whether it is m/z 69 or m/z 219. Possible cause: air leak? bad filament? dirty ion source? ...