Assay of quaternary ammonium antimicrobial compounds by aqueous potentiometric titration

Abstract

An automatic potentiometric titration method for the determination of quaternary ammonium antimicrobial compounds at the macro level is described. The procedure involves the use of standard sodium lauryl sulfate as the titrant and a nitrate ion-selective or surfactant electrode to detect the end point. The method, which includes a new, simpler means of titrant standardization, avoids the use of hazardous solvents such as chloroform, which are employed in two-phase titration methods currently in common use. In this study, four frequently produced antimicrobial quats were titrated potentiometrically and by a two-phase titration using bromphenol blue as the indicator. Comparison of results shows the automatic potentiometric method to be accurate, more precise, easier, faster, and generally better suited for use in a production laboratory than the two-phase approach. The nitrate and the surfactant electrodes appear to be equal in performance.