In this work, we extend our investigations regarding the separation of urinary nucleosides
by MEKC with the ionic liquid type surfactant 1-tetradecyl-3-methylimidazolium bromide
(C14MImBr). We study the impact of adding alkyl- and arylboronic acids (in the presence
of C14MImBr micelles) to the separation of these highly hydrophilic metabolites and
investigate the mechanism of interaction between the negatively charged nucleosides
(the negative charge is acquired either due to deprotonation of the amidic group and/or
complexation with boronate) and the positively charged pseudostationary phase. This
interaction is not only due to electrostatic (Coulombic) forces, but also due to hydrophobic
interaction of the alkyl or aryl group of the boronate that forms a complex with the cisdiol
group of the nucleoside. In this case, alkylboronates can act as a cosurfactant that
increases the partitioning coefficient of the analytes into the micelles. In the presence of
an alkylboronate in the BGE (employing only 20 mmol/L C14MImBr), the retention factors
of the studied analytes are increased considerably when compared to a BGE without this
additive. It is shown that the concept of one-site hydrophobically assisted ion exchange can
be applied to describe the observed retention behavior. The high selectivity of boronates
toward cis-diol-containing compounds can be used to adjust selectively the migration
behavior of members of this compound class. By adding alkylboronic acid to the BGE, the
separation selectivity is fine-tuned so that interferences from matrix components can be
avoided in real sample analysis.