923 (2001) 107–117 Journal of Chromatography A, www.elsevier.com / locate / chroma Reversed-phase separation of basic tricyclic antidepressants using buffered and fluoroform-enhanced fluidity liquid mobile phases * Jun Zhao, Susan V. Olesik Ohio State University, Department of Chemistry, 100 W . 18th Ave., Columbus, OH 43210-1153, USA Received 7 July 2000; received in revised form 18 April 2001; accepted 25 April 2001 Abstract In an effort to expand the range of applications of enhanced-fluidity liquid chromatography (EFLC) to strongly polar and basic analytes, fluoroform (CHF ) was investigated as a fluidity-enhancing agent. Fluoroform was chosen due to its high 3 polarity, low viscosity and chemical inertness toward water and basic analytes. A group of representative basic compounds, tricyclic antidepressants, covering a wide range of polarity was chosen as model compounds. Their retention behavior on a C stationary phase in methanol / phosphate buffer and methanol / phosphate buffer / CHF mobile phases was characterized. 18 3 The chromatographic performance with mobile phase conditions of different pH, with and without CHF addition and with 3 addition of triethylamine was studied. The advantages of using CHF enhanced and buffered mobile phases were shown in 3 the much improved chromatographic performance, such as shortened analysis time, increased efficiency, lower pressure drop and improved selectivity. Furthermore, this study demonstrated for the first time, that a commercial instrument could be readily utilized for EFLC separations which greatly expands the application range of the EFLC technique and chromato- graphic instrumentation.  2001 Elsevier Science B.V. All rights reserved. Keywords: Enhanced-fluidity liquid; Mobile phase composition; Fluoroform; Tricyclic antidepressants 1. Introduction problems associated with surface residual silanol groups, such as peak broadening, poor peak shape The separation of strongly polar and basic com- and irreproducible retention. pounds has remained one of the most difficult tasks Enhanced-fluidity liquid chromatography (EFLC) in reversed-phase high-performance liquid chroma- has been continuously growing because it is capable tography (HPLC). Due to their high column ef- of solving a wide range of separation problems. ficiency, ease of use, flexibility and wide applicabili- Liquid mixtures with enhanced fluidity that have ty, silica bonded phases are by far the most popular been characterized most comprehensively to date choices for such tasks. However, there are still many have all employed carbon dioxide (CO ) as the 2 fluidity modifier, including mixtures such as methanol/CO , methanol/H O/CO and THF/CO 2 2 2 2 [1–9]. Enhanced-fluidity liquid mixtures maintain solvent strengths similar to that of the pure organic *Corresponding author. Tel.: 11-614-292-0733; fax: 11-614- component in the mixture even when as much as 292-1685. E-mail address: olesik.1@osu.edu (S.V. Olesik). 40–50 mole% fluidity modifier is added and the 0021-9673 / 01 / $ – see front matter  2001 Elsevier Science B.V. All rights reserved. PII: S0021-9673(01)00922-0