Hydrophilic Interaction Chromatography (HILIC) Separation of Basic Drugs using MS/MS Detection Application

The basic drugs, ranitidine and paroxetine were successfully separated using hydrophilic interaction liquid chromatography (HILIC). The elution order was reversed compared to reversed-phase liquid chromatography (RPLC). Good linearity was shown over the 0.5–100 ppb levels. A spiked serum was cleaned up by protein precipitation and an aliquot was directly injected into the HILIC/ESI-MS system. Recovery was found to be 98% for ranitidine and 79% for paroxetine at the 100 ppb level. Introduction Because of its versatility, RPLC is the most widely used technique in all of HPLC. It separates molecules based on the hydrophobic interactions between the nonpolar stationary phase and the Hydrophilic Interaction Chromatography (HILIC) Separation of Basic Drugs using MS/MS Detection Application organic portions of typical analytes. However, the retention of polar analytes often requires a highly aqueous mobile phase to achieve retention. Highly aqueous systems sometimes lead to problems such as phase collapse (dewetting) [1], decreased sensitivity in mass spectroscopic detection due to poor mobile phase desolvation and ion suppression, and still may not allow retention of very polar analytes. Some specialized packings were developed to allow the use of highly aqueous systems such as polar embedded phases, hydrophilically endcapped reversed phase bonded silicas, wide-pore lowdensity bonded silicas, short-chain phases, and other special designs [2]. An alternative technique for the separation of highly polar analytes that gets around some of the problems associated with RPLC is HILIC. HILIC requires a high percentage of a nonpolar mobile phase and a polar stationary phase, similar to the requirements in normal phase chromatography (NPC). However, unlike NPC, which uses nonpolar solvents such as hexane and methylene chloride and tries to exclude water from the mobile phase, HILIC requires some water in the mobile phase to maintain a stagnant enriched water layer on the surface into which analytes may selectively partition. In addition, water-miscible organic solvents are used instead of the water-immiscible solvents used in NPC. With HILIC, sorbents such as bare silica, bonded diol, and polyhdroxyethylaspartamide are used. Polar analytes are well retained Drug Analysis