Bioequivalence and Bioavailability Forum

Dear stdev,

❝ Thank you very much for your suggestions, they were really valuable feedback! Any other possible causes that you may think would be of great help!

OK, let's try, though you have probably already thought of all of these.

The method worked initially. Was there any change afterwards in:

• instrument, particularly the autosampler and tubing (stainless steel vs. peek...)
  
• tubes used (different polypropylene tube vendor...)
  
• pipette tips
  
• mobile phase solvent (acetonitrile, methanol) provider or even batch number (I think I have somewhere a nice paper on matrix effects due to impurities in methanol depending on the provider, I'll try and have a look)
  
• mobile phase water

If you have the same problem with standards in mobile phase it should not be a problem of SPE columns batch number or extraction solvent.

Did you try with a new HPLC column ? If you still have the same problem it is not due to plasma dirt getting slowly released from it.

Do you have a second LC/MS/MS of the same make and model ? If you do, do you have the same issue on the second instrument ?

Finally, was there any re-calibration of your MS in between ? Did you try to re-do some fine tuning of your source and MS conditions ?

Regards
Ohlbe