Chromatography Forum

I recentally replaced by electron multiplier in my ms and all of a sudden I am getting huge peaks for ions 81 and 69. Which I wasn't getting before I replaced it. Any ideas what could be causing this?

Most likely you are detecting squalene, a constituent of skin oil. Always be sure to wear clean gloves when handling MS components, including the multiplier. If you pick up clean gloves with your bare hands, they are already contaminated, so it may be necessary to double glove for sensitive MS installations.

Hopefully the squalene is in your ion source, not the multiplier, and will go away following a bake or source clean at the worst. Good luck!!

Sincerely,

can't be in the multiplier because this is after the bit that separates things by mass...

IF this is an electron impact spectrum (EI; you don't specify), then this is likely to be m/z 69 = CF3 and m/z 81 = C2F3, both from the tuning compound, perfluorotri-n-butylamine.

I would go with squalene. 69 is the base peak and 81 is the next most intense peak at ~62%. 69 is the base peak in PFTBA, but the intensity of the peak at m/z 81 representing the C2F3 ion is >1%.