Study of pH dependence using molecular modeling in reversed-phase liquid chromatography of 1-phenyl-3-methyl-5-pyrazolone derivatives of aldose

A series of 1-phenyl-3-methyl-5-pyrazolone (PMP) aldose was eluted on a C₁₈ column with an acetonitrile-phosphate buffer over the range of pH 2-10 in reversed phase liquid chromatography. The relationship between the retention factor, k, and the eluent pH was expressed by an equilibrium scheme representing the probable retention process. The experimental data were fitted to the correlation curve drawn according to the equation containing the formation of the hydrogen bond with a hydroxonium ion in the eluent and the ionization of the oxygen atoms in the pyrazolone rings of the solute.The conformational changes of PMP-aldose according with the eluent pH were corroborated by computer-aided molecular modeling using quantum chemical calculations. The retention behavior was elucidated as a function of the geometrical feature of the PMP-aldose.