1106 Electrophoresis 2014, 35, 1106–1113 Katriina Lipponen 1 Sari T ¨ ahk¨ a 1 Mauri Kostiainen 2,3 Marja-Liisa Riekkola 1 1 Laboratory of Analytical Chemistry, Department of Chemistry, University of Helsinki, Finland 2 Molecular Materials, Department of Applied Physics, Aalto University, Espoo, Finland 3 Biohybrid Materials, Department of Biotechnology and Chemical Technology, Aalto University, Espoo, Finland Received July 1, 2013 Revised December 18, 2013 Accepted December 19, 2013 Research Article Stable neutral double hydrophilic block copolymer capillary coating for capillary electrophoretic separations Quaternized diblock copolymer, poly(N-methyl-2-vinylpyridinium iodide-block-ethylene oxide), was successfully used as a neutral, dynamic coating to suppress the electroosmotic flow. The block copolymer consisted of two polymers that were linked covalently together. The cationic block (poly(N-methyl-2-vinylpyridinium iodide)) was bound efficiently to the negatively charged capillary wall via electrostatic interactions, and the hydrophilic block (ethylene oxide) stabilized the system and created a neutral capillary surface with ultralow electroosmotic flow (+2.0 ± 4.5 × 10 −10 m 2 /Vs). The main advantages of the coating were simple and fast preparation, easy regeneration and automation, and stable electroosmotic flow. To emphasize the potential of this type of coating its stability was measured at a wide pH range demonstrating a high stability in the pH range of 4.0–10.5 and lifetime up to 8 days. The successful studies carried out with beta-blockers, basic proteins, and lipopro- teins proved the suitability of the coating for the separation of different sized analytes. Furthermore, the neutral coating developed is useful in a wide range of protein analysis and biological interaction studies under physiological condition. Keywords: Basic proteins / Beta-blockers / Block copolymer coating / Capillary electrophore- sis / Lipoproteins DOI 10.1002/elps.201300425  Additional supporting information may be found in the online version of this article at the publisher’s web-site 1 Introduction CE is a versatile separation technique for different biomolecules and pharmaceuticals. One of the shortcomings of this technique is still the unwanted adsorption of positively charged compounds, such as proteins and peptides, onto un- coated capillary wall. To overcome this problem numerous polymeric and copolymeric coatings have been developed dur- ing the last years [1–4]. The coating of the capillary gives also an excellent opportunity to control the electroosmotic flow for Correspondence: Professor Marja-Liisa Riekkola, Laboratory of Analytical Chemistry, Department of Chemistry, P.O. Box 55, FIN- 00014 University of Helsinki, Finland E-mail: marja-liisa.riekkola@helsinki.fi Fax: +358-9-191-50253 Abbreviations: AFM, atomic force microscopy; DHBC, double-hydrophilic block copolymer; HDL, high density lipoprotein; LDL, low density lipoprotein; MeI, methyl iodide; PEO, poly(ethylene oxide); P2QVP-b-PEO, poly(N-methyl-2- vinylpyridinium iodide-block-ethylene oxide); P2VP-b-PEO, poly(2-vinylpyridine-block-ethylene oxide); VLDL, very low density lipoprotein repeatable and reproducible separations, especially for large biomolecules. Although frequently used, covalently bound, quite neutral linear polyacrylamide coatings [5, 6] are stable at a wide pH range, their preparation is unfortunately quite laborious and time consuming. Accordingly, there is still a great need for new, especially neutral dynamic coatings with a short preparation time and applicable also under physiolog- ical pH. Among several polymers whose applicability for the cap- illary coating has been studied, the diblock copolymers belong to the less studied ones. According to IUPAC [7], block copoly- mers include two blocks with a different constitution. Either adjacent blocks differ in constitution, derived from different species of monomer or from the same species of monomer. However, in the latter case they can have a different composi- tion or different sequence distribution of the units. Materials of very different chemical nature, polarity, and size can be con- trolled and combined by choosing the most suitable blocks for each special case [8–10]. Grafted copolymers instead are, according to IUPAC [7], composed of adjacent blocks in the main chain or side-chains both of which are constitutionally Colour Online: See the article online to view Fig. 2 in colour. C  2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.electrophoresis-journal.com