Effect of ionic liquids as additives on the separation of bases and amino acids in HPLC

In this paper, four bases, including cytosine, thymine, adenine, 6-chlorouracil and four amino acids, including L-histidine, L-tyrosine, L-phenylalanine, and DL-tryptophane, were separated with different types of ionic liquids as additives for the mobile phase in high-performance liquid chromatography. Four different ILs, including 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-hexyl-3-methylimidazolium tetrafluoroborate, and 1-butyl-3-methylimidazolium chloride were used. The effects of the length of the alkyl group on the imidazolium ring and its counterion, the concentrations of the ionic liquids on the retention factor of the bases and amino acids are investigated. The results showed that the retention and resolution of the bases and amino acids were improved when ionic liquids were used as additives. The mechanism at the separation with ionic liquids as additive to mobile phase is discussed.