We have recently replaced the ESI needle on our Agilent 6100 LC-MS. All is well with the flow, but we are not able to tune our instrument. Last week, the tune looked fine, but since replacing the needle the peaks (118, 622, 922) are not found and we get a fail for the check tune. It says to calibrate the mass axis and the peak width and it still fails when you do that. I am confused as to why this occurred - it could just be an unwelcome coincidence but I'm wondering what to try next...I read something in the manual about cleaning the ion optics but I don't want to do that unless I'm really certain that that is the problem. Can anyone recommend a systematic procedure to try and narrow down the problem? Thanks.