Journal of Chromatography A, 1269 (2012) 136–142 Contents lists available at SciVerse ScienceDirect Journal of Chromatography A j our na l ho me p ag e: www.elsevier.com/locate/chroma Comparative performance of capillary columns made with totally porous and core–shell particles coated with a polysaccharide-based chiral selector in nano-liquid chromatography and capillary electrochromatography Salvatore Fanali a,∗ , Giovanni D’Orazio a , Tivadar Farkas b , Bezhan Chankvetadze c,∗∗ a Institute of Chemical Methodologies, Consiglio Nazionale delle Ricerche, Area della Ricerca di Roma I, Via Salaria Km 29,300 – 00015 Monterotondo, Roma, Italy b Phenomenex Inc., 411 Madrid Ave., Torrance, 90501 CA, USA c Institute of Physical and Analytical Chemistry, School of Exact and Natural Sciences, Tbilisi State University, Chavchavadze Ave 1, 0128 Tbilisi, Georgia a r t i c l e i n f o Article history: Available online 15 June 2012 Keywords: Nano-liquid chromatography Capillary electrochromatography Core–shell silica Enantioseparations Polysaccharide based chiral stationary phases a b s t r a c t In this study two types of silica particles, one fully porous and the other superficial porous (core–shell or fused-core) were modified with a polysaccharide-type chiral selector and evaluated for the separation of enantiomers in nano-liquid chromatography (nano-LC) and capillary electrochromatography (CEC). The major goal of this project was to critically evaluate the contribution of the “flow through particles” to enhancing peak efficiency in CEC compared to nano-LC. The better performance of fused-core silica par- ticles compared with silica particles of comparable size but having through pores questions the previous assumption that “flow through particles” is the major contributor to enhancing peak efficiencies observed in CEC. In addition, based on the results of this study it is suggested that contrary to previous reports on core–shell particles behaving poorly in narrow bore columns, these materials are quite suitable for CEC, at least in capillary columns of 100 m I.D. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Capillary electrochromatography (CEC) is a separation tech- nique governed by both chromatographic separation principles and electrokinetic migration of analytes [1,2]. If properly oper- ated, CEC provides higher separation efficiency compared to chromatographic separation techniques under otherwise similar experimental conditions. This has been systematically proven in achiral [3–6] as well as chiral separations [7–13] using CEC. Faster intraparticle mass transfer due to flow through particles has been identified as one of the major contributions to the peak efficiency enhancement in CEC experiments compared with nano-liquid chromatographic (nano-LC) experiments performed on the same capillary column [7–13]. The fact that intraparticle mass transfer in CEC experiments is faster compared to nano-LC is unquestion- able as it has been clearly illustrated experimentally by a lower C-term in the van Deemter equation [7,8], as well as based on the effects of silica pore size [9,10], ionic strength of the background electrolyte [10] and other factors [11,13] on peak efficiency in CEC. Core–shell silica particles which became commercially available recently have a nonporous core potentially prohibiting (or at least ∗ Corresponding author. Tel.: +39 0690672256; fax: +39 0690672269. ∗∗ Corresponding author. Tel.: +995 322 290648; fax: +995 32 913369. E-mail addresses: salvatore.fanali@imc.cnr.it (S. Fanali), bezhan chankvetadze@yahoo.com (B. Chankvetadze). impeding) flow through particles. Thus, a comparative evaluation of the performance of totally porous and core–shell materials in nano-LC and CEC should provide experimental evidence of the con- tribution by intra-particle flow in enhancing peak performance in CEC compared to nano-LC. In addition, the current opinion is that core–shell particles do not perform as well in smaller bore (2.1 mm I.D.) columns as in standard columns of 4.6 mm I.D. [14–17]. The advantages of chi- ral stationary phases (CSPs) based on core–shell silica in standard diameter HPLC columns have been recently demonstrated [18]. It seems interesting to evaluate the performance of core–shell par- ticle based chiral capillary columns as such columns should prove even less efficient given their even lower column internal diameter to particle diameter ratio compared to 2.1 mm I.D. columns. In order to answer the above questions, two polysaccharide- based CSPs were prepared by coating the same cellulose derivative on core–shell and totally porous silica particles. These materials were evaluated for the separation of enantiomers in nano-LC and in CEC. 2. Experimental 2.1. Chemicals and samples All chemicals were of analytical reagent grade and used as received. Acetonitrile (MeCN), methanol (MeOH) and acetic acid 0021-9673/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.chroma.2012.06.021