1 For submission to Journal of Chromatography A 1 Rapid quantification of imidazolium-based ionic liquids by hydrophilic interaction 2 liquid chromatography: Methodology and an investigation of the retention 3 mechanisms 4 Cory A. Hawkins*, Anna Rud, Margaret L. Guthrie, and Mark L. Dietz 5 Department of Chemistry and Biochemistry 6 University of Wisconsin – Milwaukee 7 Milwaukee, WI 53211 8 9 Abstract 10 The separation of nine N,N'-dialkylimidazolium-based ionic liquids (ILs) by an 11 isocratic hydrophilic interaction high performance liquid chromatographic method using 12 an unmodified silica column was investigated. The chosen analytical conditions, using a 13 90:10 acetonitrile-ammonium formate buffer mobile phase on a high purity, unmodified 14 silica column were found to be efficient, robust, and sensitive for the determination of ILs 15 in a variety of solutions. The retention window (k’ = 2 to 11) was narrower than that of 16 previous methods, resulting in a 7-minute runtime for the nine IL homologues. The lower 17 limit of quantification of the method, 2-3 mol L -1 , was significantly lower than those 18 reported previously for HPLC-UV methods. The effects of systematically modifying the 19 IL cation alkyl chain length, column temperature, and mobile phase water and buffer 20 content on solute retention were examined. Cation-exchange was identified as the 21 dominant retention mechanism for most of the solutes, with a distinct (single methylene 22 group) transition to a dominant partitioning mode at the highest solute polarity. 23 24 Keywords: ionic liquid determination; HPLC; aqueous normal-phase; rapid separation; 25 mixed-mode retention 26 27 _____________________________________________ 28 *To whom correspondence should be addressed. 29 Cory A. Hawkins 30 University of California, Irvine 31 Department of Chemical Engineering and Materials Science 32 916 Engineering Tower 33 Irvine, CA 92617 USA 34 Email: cahawkin@uci.edu; 35 36 © 2016. This manuscript version is made available under the Elsevier user license http://www.elsevier.com/open-access/userlicense/1.0/