HPLC Analysis of Codeine Formulation: Influence of Buffer Concentration and pH on Separation

Codeine and two parabens were separated using mixed-mode chromatography on the Zodiac HST C column. Codeine is retained through a combination of reversed-phase and cation-exchange mechanisms, while parabens are retained primarily by the reversed-phase mechanism.

The retention time of codeine can be fine-tuned by adjusting the acetonitrile content, buffer concentration, and buffer pH. The mobile phase and separation conditions are fully compatible with UV, ELSD, LC/MS, and preparative chromatography. A variety of organic or inorganic acids and buffers can be employed for flexible method development.

Codeine is a hydrophobic basic drug commonly used in pharmaceutical formulations as an analgesic, antitussive, anxiolytic, and sedative. It is widely administered for moderate pain and cough relief and is typically formulated as tablets or syrups. These drug compositions often include preservatives such as methyl paraben, propyl paraben, and benzoates.

A mixture of codeine, methyl paraben, and propyl paraben was successfully separated using the Zodiac HST C mixed-mode reversed-phase cation-exchange column. Codeine is retained through a combination of reversed-phase and cation-exchange interactions, while the parabens are retained via the reversed-phase mechanism alone.

The Zodiac HST C column eliminates the need for external ion-pairing reagents, as its stationary phase contains an embedded ion-pairing group, providing efficient and robust separation.