6550 QTOF problems with sensitivity

[sartaj]

Hi,

I turned on 6550 iFunnel QTOF after a long shutdown state. Vaccum builup took a long time but now I am able to operate it. However, there is steep dip in sensitivity in positive mode. I used to observe 0.5 M counts average intensity, now it is in few thousands. When I tuned the machine in positive as well as negative mode, the issue did not get resolved.

Further, I prepared fresh tune mix, cleaned source and nebulizer.

Please provide suggestions to improve the response of the MS.

Thanks,
SAM

[carlo.annaratone]

Firstly I would clean thoroughly the source, replacing key parts as the electrospray needle. If it does not do the job, I would clean the MS inside, as per maintenance manual. Bu I do know that microplate detectors and electromultipliers do not like to be exposed to air (or anything else than vacuum) so maybe that is the problem