There days I was facing one challenge when doing MD and MV. I need to use rat and pig' plasma as matrix. I used to spike the solvent with different concentrations into the plasma to make STD and QC samples. But in pig study, the LQC were always lower the acceptance (+-15%), we changed different person to repeat the operation, the results were all the same. So we changed the preparation way from spike into using plasma to dilute analyte directly into different concentrations to make STD and QCs, and the results were good. So my confusion are:

1. why? is this species difference?

2. can I use spike way to do rat MV and dilution way to do pig MV? These MVs need to be used in the IND filling. Do I need to do some extra work to prove anything?

Thank you in advance.