Model Of Hydrogen-bonding Effects
Model of hydrogen-bonding effects
in liquid-solid chromatography
N.V. Nikolenko, A.P. Korpach
Ukrainian State Chemical Technology University,
Gagarin av. 8, 49005 Dniepropetrovsk, Ukraine,
e-mail: nick@academy.dp.ua
At present Snyder retention model, which is based on displacement of adsorbed mobile phase molecules by adsorbing solute molecules and localization effects, provides an adequate physical basis to describe different adsorbents. However, in addition to displacement and localization effects, the hydrogen bonding between sample and solute molecules in polar solvents can also play an important role in affecting sample retention and solvent selectivity. A theoretical description of hydrogen bonding effects can be made from model of charge-controlled adsorption [1].
The model of charge-controlled adsorption assumes that adsorption energy of polar molecules on silica or alumina is described by equation:
Eads = E12 – E23 – E13 ~ Q1Q2 – Q2Q3 – Q1Q3*
where the indexes 1, 2 and 3 designate adsorbent, adsorbate and solvent, Eij – energy of electrostatic interaction, Qij – effective charges of atoms. The angular factor DE/DQ of Eads(Q2)-dependences determines selectivity of adsorbents in liquid-solid chromatography:
a = exp(DE/DQ(QN – QK)) = exp(Q1 –Q3)(QN – QK),
where the indexes N and K designate different adsorbates.
The obtained equality shows that with reduction of Q3 for mobile phase the selectivity of adsorbent is naturally increased. If the reduction of Q3 does not allow receiving required selectivity, it is necessary to use new adsorbent with the large effective charges Q1 of the reactionary centers.
Application of the model to experimental data for high-performance liquid chromatography of polar aromatic compounds on silica shows a good agreement between theory and experiment.
References
1. Nikolenko N.V., Taran, I.B., Plaksienko, I.L., Vorob’ev, N.K., Oleinik, T.A. //Colloid Journal. 1999. V.61. P.488.
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