Without dilution, drugs which are poorly water soluble may precipitate from biorelevant medium at room temperature after sampling. Immediately diluting biorelevant dissolution samples with an appropriate organic diluent prevents drug precipitation. Sample precipitation is undesirable as it can cause column damage and adversely affects the quality of HPLC results. Furthermore, undiluted biorelevant media (especially fed state) can reduce the efficiency of stationary phase, increase the pressure and block the detector cells.

The diluent should prevent these potential problems and keep the biorelevant dissolution sample physically and chemically stable at room temperature. It should maintain the drug in solution and keep the sample homogeneous during analysis by HPLC (usually about 24 hours).

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