We have a LC Packings Ultimate-Switchos-Famos coupled to Applied Biosystems QStar Mass Spec. I believe it is a typical set-up for most people doing shotgun proteomics.

We are picking up a peak at m/z= 327 to 329 with quite high intensity (~1500 cps). We cannot work out what it is- we have changed buffers, ion source, nitrogen gas source and can't seem to reduce or remove this peak.

Has anyone come across this problem or know what the hell this peak is??

Please please help!

EuhaloJags