Published:Journal of Chromatographic Science,
ISSN 0021-9665 Volume 45,
Number 5, May/June 2007, pp.256-262
Effects of Ionic Liquid as Additive and the pH
of the Mobile Phase on the Retention Factors of Amino Benzoic
Acids in RP-HPLC
J. Zheng, Y. Polyakova, and K.H. Row
Center for Advanced Bioseparation Technology, Department of Chemical
Engineering, Inha University, Incheon 402-751, South Korea
As an organic salt, ionic liquids are widely used
as new solvent media. In this paper, three positional isomers,
such as o-amino benzoic acid, m-amino benzoic acid, and p-amino
benzoic acid are separated with four different ionic liquids as
additives to the mobile phase using reversed-phase (RP) high-performance
liquid chromatography (HPLC). Amino benzoic acids are biologically
active substances; the p-isomer is present in a group of water-soluble
vitamins and is widely known as a sunscreen agent. The ionic liquids
used are 1-butyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium
tetrafluoroborate, 1-ethyl-3-methylimidazolium methylsulfate,
and 1-octyl-3-methylimidazolium methylsulfate. The effects of
the length of the alkyl group on the imidazolium ring and its
counterion, the concentrations of the ionic liquid, and the effect
of the pH of the mobile phase on the retention factor of the amino
benzoic acid isomers are studied. Separation with the ionic liquid
in the eluent was better than the separation without the ionic
liquid. The pH mainly affected the retention and elution order
of the solutes in RP-HPLC.
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