I am having a problem in deciding the diluent for Related substances.

My Assay diluent contains Water:ACN:MeOH::20:40:40, pH 3.0 with OPA in which recovery is 100%.

The RS method earlier developed contains ACN:MeOH::50:50.

The problem with the RS diluent is that it doesn't give the 100 % recovery in case of Assay.

Can I go ahead with ACN:MeOH::50:50 diluent.

Is it mandatory to have RS method having 100% recovery for drug Substance?