Preservatives can be classified into one of three categories: those that inhibit growth of bacteria, yeasts or molds (antimicrobials); those that slow air oxidation of fats and lipids (antioxidants) that cause rancidity; and those that block the natural ripening and enzymatic processes that continue to occur in foodstuffs after harvest. In this work, we investigate the effects of mobile phase pH and tetramethylammonium chloride (positive ion-interaction reagent) concentration on the separation of two antimicrobial preservatives, benzoic acid and ethyl paraben, and 4-hydroxybenzoic acid. Future work will test the methods by quantifying the preservative content of various commercial products. Additional studies will examine the effects of pH and a negative ion-interaction reagent.