Abstract: Hydrophobic solvent such as chloroform can be used as modifier to induce phase separation of the acetonitrile aqueous mixture. Capitalizing on this phase transition phenomenon, a novel approach, named solvent induced phase transition extraction(SIPTE), was proposed to extract drug in plasma. SIPTE is superior to conventional liquid-liquid extraction(LLE) as the recovered acetonitrile solution can be directly injected into the RP-LC system, which greatly simplifies the sample preparation procedure. Furthermore, the proposed SIPTE is excellent due to the function of automatically preconcentrating the sample. Nitrendipine was used as the test drug to design and validate the SIPTE method. Nitrendipine was separated on a RP-C₁₈ column, using acetonitrile/water containing 20 mmol/L of ammonium formate(70∶30, volume ratio) as the mobile phase. Nimodipine was selected as the internal standard for the quantification purpose. The obtained good linear, accuracy and precision results prove that the SIPTE method is sensitive and accurate enough to be used for pharmacokinetic study.

Key words: Solvent induced phase transition extraction(SIPTE), HPLC-MS, Nitrendipine, Nimodipine