HIGH PERFORMANCE METAL CHELATE INTERACTION CHROMATOGRAPHY

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A diethylenetriamine functional stationary phase, capable of complexing transition metal ions, was developed and evaluated for use in HPLC separations. Synthesis involved evaporation of the trimethoxysilylpropyl-monomer from acetate buffered aqueous solution and derivatization at 200 degrees C and 0.55 torr. Reproducible surface coverages of 3.0 micro moles/m-squared were obtained on 100-angstrom, 550 m-squared/g silica. Analytical columns were loaded with Cu(II), Ni(II) and Zn(II) by frontal elution process; breakthrough volumes corresponded well with metal uptake determined by atomic absorption spectrophotometry. Buffered aqueous-organic mobile phases were used for separations of sulfonamide antimicrobials that included sulfa-diazine, sulfa-thiazole, sulfa-merazine and sulfa-pyridine. An empirical retention expression was developed that related chromatographic retention to: a) electrostatic interaction of the acidic sulfonamide function with the cationic stationary phase, b) secondary metal-ligand complexations involving the heterocyclic aromatic substituents of the solutes and c) solubilization of the relatively hydrophobic solutes in the mobile phase. Retentions were inversely proportional to concentrations of organic modifier and buffer and were generally directly proportional to eluent pH. An eluent of pH 7.3 phosphate buffer and 50% methanol was effective in minimizing electrostatic interactions while allowing retention based on metal-ligand interactions.