Carry over issue of Phosphatidylcholine in Shimadzu LC

[Aveline Neo]

Hi, I am new to using Shimadzu LC system with Sciex 6500 QTRAP MS. I kept seeing high levels of carry over of different PC molecular species in my analysis despite changing the flush solvents from Methanol to isopropanol to DCM/IPA (10%:90%). Changed a new needle, cleaned or changed injector seal/rotor. Did injection by pass the injector and still seeing the peak in my column. Changed a new column and still there. Different mobile phase mix also doesn't get rid of the peaks.

I was wondering if anyone uses ROMIL solvents and face the same issues before? I usually use OPTIMA LCMS grade solvents from fisher so that is one last thing I can think of trying. Anyone can suggest what can I try or what could be the reason? Thanks.

[sav]

Anyone can suggest what can I try or what could be the reason?

Phosphatidylcholines are zwitterions, so you must "canceled" it to decrease crossover. You can try to add some soft ion-pairing compounds in the eluent and needle wash solution (0.01 - 0.1 %v): TFA, Trimethylamine or Triethylamine. Start with TFA (note that TFA cause of supression of ionization in ESI). Needle wash solution = MeOH:Chloroform or MeOH:DCM (8:2 to 1:2; must be optimized).