Chromatographic separation of carbohydrates is one of the most in-demand types of analysis. There are various options for the separation of underivatized mono- and disaccharides including the most common anion-exchange chromatography with alkali eluent [1], ligand exchange chromatography (LEC) on sulphonated resins loaded with metal ions (Ca2+, Pb2) [2] and hydrophilic interaction liquid chromatography [3,4]. Hydrophilic interaction liquid chromatography (HILIC) using aminopropylsilica columns with water – acetonitrile mixtures as mobile phase has been widely used for almost 50 years for the separation of carbohydrates since 1974 [5].

The retention mechanism in HILIC is still not well identified and includes various possible interactions of different natures, which are mainly associated with the definition of the polarity of the stationary phase. In other words, the high polarity and hydrophilicity are sort of synonyms for considering properties of the stationary phase. Hemstrom and Irgum discussed the retention mechanism of this chromatographic variant in detail [3]. Briefly, two basic possibilities are considered for the possible interaction of solutes with a stationary phase. One of them is the partition of a solute between a water layer retained on the surface and the bulk of the eluent. In this case, the hydrophilicity of the solutes defines their retention as suggested by Alpert [6]. The second possibility includes a combination of interactions of solutes with functional groups, while the majority of these interactions are related to the polarity of analytes and adsorption sites. Therefore the retention of analytes is associated with either hydrophilicity or polarity of substances and the surface.

The traditional polarity scales comprise various interactions including weak non-specific dispersion (energy of 0.05–40 kJ/mol) and induction (2.0–10 kJ/mol) forces, and the stronger specific hydrogen bonding (10–40 kJ/mol), π-π interactions (up to 50 kJ/mol), ion-induced dipole (3–15 kJ/mol), dipole-dipole (5–25 kJ/mol), ion-dipole (50–200 kJ/mol) and ion-ion (100–350 kJ/mol) interactions [7]. However, none of the above mentioned approaches considered one more strong interaction, which can be also considered as polar and hydrophilic. This is a reversible coordinate bonding between sorbate and metal ion with an interaction energy of 150 −1100 kJ/mol.

The complexation of analytes with bonded functional groups in HILIC has been used for the selective separation of the anticancer drug cisplatin (cis-diammindichloroplatinum(II)) from trans-diammindichloroplatinum (II) and decomposition products by using Lichrosorb-NH2 column and acetonitrile – water (70 : 30 v/v) mixture as mobile phase [8]. Later, Falta et al. used Phenomenex Luna NH2 column for the separation of cisplatin, carboplatin, and oxaliplatin using descending acetonitrile gradient elution with acetonitrile- 0.05% formic acid eluent [9]. Strong complexing properties have been reported for classic Polycat A column packed with polyaspartic acid functionalized silica [10], [11], [12]. Potentially, a significant coordination of metals can be also expected for cyano-, mercaptoethanol-, amido-, phosphorylcholine (SeQuant®ZIC®-cHILIC) [13] and some other bonded HILIC stationary phases.

The coordination of sugars on metal ions has been exploited for their separation using sulfonated poly(styrene-divinylbenzene) gel type cation exchangers loaded with Ca2+ and La3+ with eluents containing up to 30% acetonitrile or 50% ethanol in water as the mobile phase [14]. Such content of organic solvent in the eluent is lower as compared with that normally used for the separation of carbohydrates in HILIC. However, the authors underlined that the Ca2+ and La3+ stability constants for all complexing compounds are from three to ten times higher in water – ethanol (50:50) and from two to five times higher in water – acetonitrile (70:30) mixtures than in water [15].

Obviously, the complexation in the stationary phase can modify the separation selectivity of carbohydrates under HILIC mode, especially in the eluents enriched with organic solvents. In this study, properties of a hydrophilic complexing sorbent based on silica gel with grafted groups of 2-hydroxyethyliminodiacetic acid (HEIDA-silica) in free form (H+ form) [16,17] and in the form of complexes with metal ions (Ca2+, Pb2+, and La3+) was investigated under HILIC conditions with mono-, di-, and trisaccharides as probes.