MS/MS ion drift

[zupahfly]

Hello,

I currently have a GC-MS Varian Saturn 2200. I'm using it mainly for quantification of haloanisoles by SPME. It worked just fine for almost a year. However, despite noting else changed (methods, conditions, etc..), since a few days now i'm having a problem i cannot solve and the maintenance guys can't either. I work in MS/MS mode (MRM) and i need to identify the ions 171 and 167, and my problem is that it drifts up and down and fails to identify them. What happens is that the peak is there, but under 170 or 172, and 166 or 168. What can i do to resolve this? I've tried RF tunning, mass defect adjustment but it keeps drifting around (for example to 171.6, 170.4)

Thanks very much in advance for any help

Regards,

[cleh]

It could be temperature related. Check the fans in the instrument. Even if they're working, shut the instrument down and spin them by hand to make sure they spin freely. Also, make sure you're room temp is constant and within the temp specs for the instrument.

[zupahfly]

Hi,

Thanks for your answer. Both fans are working perfectly and the room is under constant temperature (around 23ºC). I dont think that is the problem... I tried again to perform and AMD excitation to evaluate the excitations and it works fine, but the spectra are still very near of .5 and then it shifts...