Dear Ella Hasan,

Do you get no peak in standards and QCs or in unknown samples? Could it be that the concentrationa are actually below Limit of detection?

If you are concerned with response in real sample extracts compared to standards you can test over-spike / standard addition (add known concentration in selected real samples). This will reveal issues with e.g.  ion Suppression, formulation interference.

It is not unusual for intercept to be negative when using all non-Zero standards, as is common practice in bioanalytics.It is not necessarily an issue, as Long as standrds and QCs are reproducible and robust, and you do not extrapolate concentrations out of your Standard curve.

Are you taking special care with light protection of your samples, working solutions...? Sunitinib is very light sensitive, could this be part of the problems you observed? For some compounds stability may be fine in plasma but more sensitive in extracts..

Best of luck

Patrice

Dear Ella 

Absence of peaks may be due to column blockage or autosampler needle blockage.check for any carryover or extend your chromatographic run.try to change to any c18 100mm,5micron column.Use 1mm ammonium acetate with acetonitrile as mobile phase ideally it should elute faster in the column using high organic mobile phase.check for your ion source for proper spray.

Good luck

Kannadhasan

Very useful information for my work! I will gladly follow further discussion!