Dear All.

I'm writing this here because I don't have any validated person to contact for this problem.

If anyone who has knowledge in LC FLD and Aflatoxin M1, Please hope you to give us any advices for us.

The problem we got is different Aflatoxin M1 standard's signal value in ACN and Mobile phase(DW 75: ACN 25).

We dilute AFM1 std(The Stock is in ACN) with ACN only based on local method and there are no problem over an year.
But recently, the chromagram of STD dilluted in ACN (Working std) is not well.

Peak is going very lower than a month ago.
the Peak area of 15 ppb in recent days is same with 0.5 ppb in the past.

And the important thing is..
If dilute same STD with Mobile phase (DW 75 : ACN 25),
the peak is came out without any degradation.

Nothing is changed.
Same instrument, Same column, Same condition, Same Std, Same solvent.

Are there anything that can cause this?
Anything need to be doubt, including aging of consumable parts of FLD etc.

Please feel free to give any advices.