Eluent Additives and the Optimization of High‐Performance Liquid Chromatography Procedures

Abstract

High‐performance liquid chromatography (HPLC) is one of several separation techniques that are based on the differential migration of an analyte (solute) through a fixed medium as the result of a driving force, the eluent. In the case of HPLC, the eluent is typically either a binary or ternary mixture of solvents and the stationary phase is most often a porous adsorbent or a chemically bonded phase attached to a porous substrate. The rate of migration of an individual solute and the separation between groups of solutes are governed by their interactions with the stationary phase. Thus, the optimization of an HPLC method involves the selection/adjustment of the physical and chemical parameters which control the rate of migration of the solute in such a fashion that baseline resolution is obtained between it and other co‐analytes or interfering compounds within the mixture. In doing this, given a series of closely related compounds, it is important to identify structural differences between solutes and to maximize the interactions with the stationary phase arising from them. This article considers the important physical and chemical aspects of the solute, eluent, and stationary phase in terms of chemical equilibria, solute structure, eluent conditions, operational parameters, and nonideal effects. Likewise, as several approaches may lead to acceptable analytical separations, other performance criteria such as simplicity, reliability, speed, and cost also are discussed in terms of arriving at the optimal method.