Effect of Bound Copper(II) on the LC Separation of Selected Phenols Using an Aminophosphonic Acid Silica Stationary Phase

Abstract

The effects of Cu (II) on the separation of phenol and chloro‐, nitro‐, and methyl‐substituted phenols by ligand exchange chromatography using the aminophosphonic acid silica (APAS) stationary phase were investigated. Retention times for the phenols were longer, and the peaks were more asymmetric with more tailing on APAS‐Cu(II) compared with the APAS. However, by using the mobile phase of hexane/dichloromethane/methanol and 5‐µm bonded APAS‐Cu (II) particles, good separation was achieved for a number of mixtures among the 12 compounds studied. This chromatographic system, however, did not resolve many of the most closely related compounds of interest. The order of elution can be explained by a separation mechanism involving complexation of phenols with Cu (II) on the APAS‐Cu (II) stationary phase, as well as van der Waals forces and hydrogen bonding. Excellent recovery, good linearity in response, and low detection limits (0.1–1 mg/L) were achieved. Capacity factors remained stable (1–2% relative standard deviation) for repeated column use over several days.

Keywords:

• Aminophosphonic acid silica
• Phenols
• Ligand exchange chromatography

Acknowledgments

The authors would like to express their thanks to the Postgraduate Education and Research Program in Chemistry for financial support of this work. Also, we are grateful to Assistant Professor Dr. Viwat Hahnvajanawong for helpful discussions.