966 (2002) 81–87 Journal of Chromatography A, www.elsevier.com / locate / chroma Immobilized artificial membrane chromatography coupled with atmospheric pressure ionization mass spectrometry 1 * ´ ´ April C. Braddy, Tamas Janaky , Laszlo Prokai Center for Drug Discovery, College of Pharmacy, University of Florida, Gainesville, FL 32610-0497, USA Received 29 August 2001; received in revised form 2 May 2002; accepted 17 May 2002 Abstract Liquid chromatographic separations on monolayers of cell membrane phospholipids covalently immobilized to silica particles at high molecular density is used for mimicking solute partitioning into biological membranes that generally correlates with membrane transport. This technique called immobilized artificial membrane chromatography usually employs ultraviolet (UV) detection where a single compound is analyzed in a chromatographic run limiting thereby its throughput for drug discovery applications. For coupling with atmospheric pressure ionization mass spectrometry, the phosphate-buffered saline mobile phase was replaced with one that used ammonium acetate as a volatile buffer. While atmospheric pressure chemical ionization accommodated a purely aqueous effluent, interfacing with electrospray ionization required effluent splitting and the addition of an organic modifier (5%, v / v, acetonitrile). Neuropeptide FF antagonists as early-phase drug candidates were used for the comparative evaluation of the methods. Whereas electrospray ionization produced essentially no fragment ions, several compounds involved in our study yielded low-abundance molecular ions with atmospheric pressure chemical ionization. The use of mass spectrometry yielded data that correlated well with those obtained by the method employing UV detection. Both atmospheric pressure ionization methods permitted the simultaneous determination of the 9 k capacity factors and, therefore, an increased-throughput ranking of potential new leads emerged from the drug IAM discovery process based on affinity to artificial membranes.  2002 Elsevier Science B.V. All rights reserved. Keywords: Membrane chromatography; Interfaces, LC–MS; Peptides 1. Introduction drug candidates through the membrane is essential in early-phase drug discovery. Membrane partitioning A common biological process is the interaction of usually affects a drug’s activity, toxicity, absorption, drug molecules with cell membranes. The ability to distribution, metabolism, and its pharmacokinetic determine membrane interaction and diffusion of properties. There are several in vitro models in which drug permeation through membranes can be estimated. Caco-2-cells [1,2] and intestinal tissue [3] *Corresponding author. Tel.: 11-352-392-3421; fax: 11-352- are common methods employed, but they are both 392-3421. time-consuming and costly. Another commonly used E-mail address: lprokai@grove.ufl.edu (L. Prokai). 1 method is n-octanol–water partitioning [4], which On leave from the Department of Medical Chemistry, Uni- versity of Szeged, Hungary. has limitations because it often reflects only the 0021-9673 / 02 / $ – see front matter  2002 Elsevier Science B.V. All rights reserved. PII: S0021-9673(02)00700-8