Incredible reduce in AUC

[sara allen]

Dear reader
I have a vitamin A+D drop sample and I want to assay vitamin A$D . I use C18 column as stationary phase and mixture of CH3OH/ACN/ Hexane (46.5/46.5/7) as mobile phase and THF/ ACN (1/1 ) as diluents. AUC for vitamin A std (about 2200) but in the last 2times it is reduced to about 70. I checked the concentration , wavelength, mobile phase, diluents, but I can’t understand what happened.
Please Don’t hesitate me

[tom jupille]

Try injecting a sample or standard that contains more than one peak. If the response for all the peaks is lower than expected (by the same proportion), you probably have a malfunctioning autosampler.

[Bryan Evans]

Hi Sara

Do you have to separate D2 from D3?