decrease m/z135，152，253，391

[pyao]

Hi,
When I use the Agilent 1200 HPLC and Finnigan LCCQAdvantageMAX to get the BG with the mobile phase of 85%water/15%MeOH, m/z135, 152, 253, 391 are so high. I think they are something contaminated, do you have some suggestions to decrease these valvues?
Thanks!

[willnatalie]

I had a lot of issues with 391m/z. I had to switch out most to all of the plastic tubing. Also had a N2 generator that could have caused this issue as well so I switched to a larger doer. Hope this helps.

[lmh]

391 is usually a common phthalate (dioctyl I think, can't remember). It's found in solvents, tubing, plastics anywhere, it just happens. My lab finds that if we keep using solvents fast enough, it isn't a major problem. If your instrument is new, just use it lots, and it'll probably get less. Note that if you have a sodium-rich method you'll start getting 413 isntead, and you may also get 279 at some point, another phthalate. Look on the bright-side, if you ever do accurate mass, they make quite useful internal standards!

[pyao]

Thanks a lot!