A reference standard composite was prepared that contained the active pharmaceutical ingredient sunepitron and three potential impurities. This standard was characterized and used for concomitant quantitation of sunepitron and its potential impurities in samples of drug substance and drug product. This approach minimizes the number and quantity of reference standards which often are expensive to synthesize, characterize, and maintain. In addition, running assays becomes simpler because the number of reference standard solutions required for each assay is reduced. Reference standard composites can also be used for qualitative applications such as demonstrating system suitability or for retention times markers for process related impurities or degradants.