Author's personal copy Journal of Chromatography A, 1217 (2010) 5665–5673 Contents lists available at ScienceDirect Journal of Chromatography A journal homepage: www.elsevier.com/locate/chroma Aliphatic carboxylic acids and alcohols as efficiency and elution strength enhancers in micellar liquid chromatography Alexander P. Boichenko a,∗ , Alain Berthod b a Department of Chemical Metrology, V.N. Karazin Kharkov National University, Svoboda sq. 4, 61077 Kharkov, Ukraine b Laboratoire des Sciences Analytiques, CNRS, Universite de Lyon 1, 69622 Villeurbanne Cedex, France article info Article history: Received 5 March 2010 Received in revised form 21 June 2010 Accepted 1 July 2010 Available online 31 July 2010 Keywords: Micellar liquid chromatography Organic modifier Sodium dodecylsulfate Aliphatic carboxylic acids Elution strength Selectivity Efficiency Temperature abstract Micellar liquid chromatography (MLC) uses surfactant solutions as mobile phases with added organic additives to enhance both the elution strength and the chromatographic efficiency. Two aliphatic car- boxylic acids (1-butanoic and 1-pentanoic) were used as MLC additives and compared with the two corresponding alcohols (1-butanol, 1-pentanol) in terms of elution strength, efficiency and selectivity. A set of 11 phenol derivatives was used as probe compounds. All micellar mobile phases were prepared with sodium dodecylsulfate (SDS) with concentration ranging from 0.05 to 0.15 M and the modifier content within 1.0 and 5.0% (v/v). The elution strength of different mobile phases containing a constant amount of SDS and different amounts of modifiers; and mobile phases containing a constant amount of modifier and different SDS concentration were determined and discussed. The effect of the acid modifiers on efficiency was studied constructing van Deemter plots that showed no minimum within the 0.01–0.7 mL/min flow rate range studied. Temperature effects were also studied constructing the classical van’t Hoff plots. The slight curvature of the plots in the 25–70 ◦ C range may indicate some modification of the surfactant- bonded moiety layer on the stationary phase surface. Since no definitive advantage of the use of aliphatic acids were established compared to their alcohol counterpart, their terrible smell will probably preclude their use as MLC organic modifiers. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Micellar liquid chromatography (MLC) uses the standard HPLC equipment. Simply, the mobile phases are aqueous solutions of surfactants, modified by small amounts of organic solvents. MLC was developed over the last three decades as a possible “green” and inexpensive alternative to classical RP-HPLC [1–3]. During last years, considerable progress was achieved in the understand- ing of MLC separations. It is now possible to control separations using different surfactants, organic modifiers, pHs, temperatures and column types. Robust, fast and validated MLC methods were developed for pharmaceutical, clinic, environmental analysis. Now, MLC is a powerful complementary tool in current analytical chem- istry. Compared to classical HPLC, MLC has several advantages such as separation of complex mixtures of compounds with different hydrophobicity in isocratic mode and direct injection and simpler sample preparation in the analysis of biological fluids. Since the beginning of the MLC development it was realized that MLC will never supplant classical HPLC. MLC is a valuable option ∗ Corresponding author. Tel.: +380 509151791. E-mail address: Alexander.P.Boichenko@univer.kharkov.ua (A.P. Boichenko). especially when biological sample are treated. In 1983, Dorsey et al. explained that the low efficiency for MLC was due to a poor mass transfer on bonded stationary phase [4]. They showed that the addi- tion of 3% (v/v) 1-propanol to sodium dodecyl sulfate (SDS) micellar mobile phases associated to a 40 ◦ C column temperature improved the MLC efficiency significantly. As a result, most of MLC separations are conducted today using aqueous micellar solutions modified by small amounts of organic solvents [3]. The factors affecting the effi- ciency of MLC separations were thoroughly investigated [5–10]. Recently, the systematic investigation of a series of macroporous and specially bonded stationary phases in MLC mode has been com- pleted [11–13]. It was found that acceptable efficiencies could be reached in MLC using stationary phases bonded with short chain alkyl chain or a fluorooctyl chain [13]. The first conclusions formu- lated by Dorsey et al. [4] were fully confirmed recently performing MLC with 12 different stationary phases [14]. The added organic modifiers improve efficiency and affect elution strength and selectivity [15–21]. Several empirical and mechanical retention models have been proposed to take into account the presence of modifiers in micellar mobile phases [22–25]. The models allowed to develop optimization procedures which can be used to find quickly the best surfactant con- centration and modifier proportion in a micellar mobile phase 0021-9673/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.chroma.2010.07.001