Analysis of ionic compounds by reversed-phase HPLC requires the pH of the eluent to be controlled with acid or buffering agent. The pH control stabilises the dissociation state of compounds and enhances the reproducibility of retention and separation. Unsuitable pH in analysis causes problems such as a double peaks or peak broadening. As shown in the figure below; the same compound eluted at pH4.8 shows a double peak, whilst at pH7.0 it shows a single sharp peak. When analysing an ionic compound, finding the optimum pH range for each functional group will result in avoiding such problems.