ionization stability on API 2000

[Maristela]

Dear friends

I am working with determination of mycophenolic acid in plasma samples by LC-MSMS.
I developed a method to exctract and optimized the MS.

I have a variation of ±10% between injections (n=7-15) of the same vial no matter if I test pure standard or extracted sample.

mobile phase> acetonitrile-acetic acid 1mM (8_2) isopropanol 5%
ion source temperature> 450°C
flow 0.8ml_min
split 1_1

Does anybody has an idea about the reason of this variation ? I am not working with my limit of quantitation value in other words, it is not a matter of low concentration.

Hope to hear from you soon......

[OtherGeoff]

Hi Maristela

When you say you have a variation of 10% do you mean the absolute peak areas or the ratio to the internal standard. What internal standard are you using? mycophenolate can be difficult if you use the wrong one.