A preliminary investigation of ghost peaks in a reversed-phase gradient HPLC system

Abstract

This study involves a reversed-phase gradient HPLC related substances (impurity) analytical method, for a drug product. These types of analyses are of crucial importance because the data they supply is such that it might be part of qualifier information used by regulatory organisations to determine whether marketing authorisations applications are to be accepted or not. Problems were observed in this method as ghost peaks were coinciding with the retention time of the active pharmaceutical ingredient (API) and also appearing at relative retention times of probable related substances of the API, thus making the quantification of such impurities difficult. Ghost peaks is the most common recently used term for non-reproducible, random and uncontrollable peaks, for which several terms were coined in the past decades including spurious peaks, vacant peaks, eigen peaks and system peaks. They are more important in reversed-phase gradient analytical systems which tend to be more able to concentrate any contaminants present in the system as the organic component of the mobile phase varies (increases). This investigation involved a preliminary analysis of the situation, the primary aim being the determination of the source of the ghost peaks should their source be one and consistent, and hence the eradication of peaks by taking limited precautionary measures thus avoiding the re-development and/or revalidation of the method.