LC-MS contamination m/z 391 and 285

[MHV]

Hi,

I've had trouble with phthalate contamination (dioctyl phthalate, m/z 391) for the past few weeks and can't find the source of the contamination but so far it seems to be coming either from the water used in mobile phases or from the LC system itself. Has anyone had problems with phthalate contamination? Where was the source?

Also, when using ACN, a new contamination peak appears, m/z 285, does anyone know what it could be? This last peak appears only when using ACN (while the m/z 391, 413 and 429 from the phthalate are always there, no matter what solvent is used!).

Thanks a lot for your help!!

MHV

[Uwe Neue]

Connection tubing in your deionized water lines?

[MHV]

Thanks for your reply.

According to the equipment maintenance staff, there are no plastic tubing connected to the water purification system. Some of the tests we made indicate a contamination in formic acid (3 bottles of varying manufacturers and uses all tested positive). Could the contamination be from pipette tips used to prepare mobile phases? I also obtained diverging opinion concerning PEEK tubing, have you heard of phthalate contamination in PEEK before?

Many thanks