Journal of Chromatography A, 1218 (2011) 1988–1994 Contents lists available at ScienceDirect Journal of Chromatography A journal homepage: www.elsevier.com/locate/chroma Monolithic silica rod columns for high-efficiency reversed-phase liquid chromatography Shota Miyazaki a,∗ , Masakazu Takahashi a , Masayoshi Ohira a , Hiroyuki Terashima b , Kei Morisato c , Kazuki Nakanishi c , Tohru Ikegami d , Kanji Miyabe e , Nobuo Tanaka a,d a GL Sciences Inc., 237-2 Sayamagahara, Iruma, Saitama 358-0032, Japan b GL Sciences Inc., 5-3 Nagasone, Okajima, Fukushima 960-8201, Japan c Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan d Kyoto Institute of Technology, Sakyo-ku, Kyoto 606-8585, Japan e Toyama University, Faculty of Engineering, Gofuku, Toyama 930-8555, Japan article info Article history: Available online 2 December 2010 Keywords: Monilithic silica rod column HPLC Reverse phase Faster separation High efficiency Low back-pressure abstract Chromatographic properties of a new type of monolithic silica rod columns were examined. Silica rod columns employed for the study were prepared from tetramethoxysilane, modified with octadecylsilyl moieties, and encased in a stainless-steel protective column with two polymer layers between the silica and the stainless-steel tubing. A 25 cm column provided up to 45,000 theoretical plates for aromatic hydrocarbons, or a minimum plate height of about 5.5 m, at optimum linear velocity of ca. 2.3 mm/s and back pressure of 7.5 MPa in an acetonitrile–water (80/20, v/v) mobile phase at 40 ◦ C. The permeability of the column was similar to that of a column packed with 5 m particles, with K F about 2.4 × 10 -14 m 2 (based on the superficial linear velocity of the mobile phase), while the plate height value equivalent to that of a column packed with 2.5 m particles. Generation of 80,000–120,000 theoretical plates was feasible with back pressure below 30 MPa by employing two or three 25 cm columns connected in series. The use of the long columns enabled facile generation of large numbers of theoretical plates in comparison with conventional monolithic silica columns or particulate columns. Kinetic plot analysis indicates that the monolithic columns operated at 30 MPa can provide faster separations than a column packed with totally porous 3-m particles operated at 40 MPa in a range where the number of theoretical plates (N) is greater than 50,000. © 2010 Elsevier B.V. All rights reserved. 1. Introduction The development of columns for reversed-phase HPLC that can provide higher overall performance (column efficiency, permeabil- ity, and separation time combined) compared to columns packed with small totally porous particles has been attracting attention. While columns packed with sub-2 m totally porous particles pro- vide high efficiency at high speed, they require high pressure to achieve fast separations, and the chromatographic system needs to be optimized for efficient operation of small-sized columns [1–3]. Columns packed with 2.6–2.7 m superficially porous par- ticles showed similar column efficiency as columns packed with sub-2 m particles with significantly higher permeability [1,4]. The properties of such columns have been reported in detail [4]. Several types of superficially porous particles are commercially available, ∗ Corresponding author. Tel.: +81 4 2934 2123; fax: +81 4 2934 3412. E-mail address: s-miyazaki@gls.co.jp (S. Miyazaki). and the development of smaller core–shell particles has been con- tinued [5]. Monolithic silica columns can also provide higher efficiency per unit pressure drop compared to conventional columns packed with totally porous particles. This is based on the presence of small- sized skeletons and large through-pores, or the large (through-pore size/skeleton size) ratios [6,7]. The high permeability allowed the operation of a long column system to yield large numbers of theoretical plates under moderate back pressure [8,9]. The chro- matographic properties of rod-type monolithic silica columns were discussed in relation to the silica structure in early reports [10,11] as well as for commercial materials in detail [6,12,13]. A monolithic silica rod column prepared from tetramethoxysi- lane (TMOS), Chromolith, was first commercialized in 2000, followed by similar products, Onyx, distributed later by another company. The silica rod columns with through-pore size of about 2 m, mesopore size of 13 nm [14,15] clad with an engineering plastic, polyether–ether–ketone (PEEK), provided column effi- ciency equivalent to a column packed with 3.5–4 m particles, or 0021-9673/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.chroma.2010.11.032