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.Paper no. S1240 in JSD 5, 117-121 (April 2002).KEY WORDS: Automatic titrator, boric acid buffer, Hyamine ® 1622, nitrate ion selective electrode, sodium lauryl sulfate, surfactant electrode, two-phase titration.Quaternary ammonium antimicrobial compounds (referred to herein as quats) are widely used as hard-surface disinfectants, deodorizers, fungicides, algicides, slimicides, and sanitizers in households, nursing homes, hospitals, building maintenance, public institutions, cooling water applications, and food processing. The production of these quats requires analytical methods for their assay that are fast and accurate for process and quality control and to ensure final product compliance to specifications. With today's emphasis on safety and ecological concerns, it is also imperative that the methods avoid the use of solvents that are hazardous to laboratory workers or to the environment. A number of methods have been proposed over the years for assaying quats. A colorimetric procedure based on the reaction of the cationic salt with an anionic dye, extraction of the dye complex with chloroform, and measurement of the color absorbance with a spectrophotometer was reported by Auerbach (1). The method has proven to be useful at lower (ppm) levels but not at macro levels. Probably the most commonly used method is a modification of the one originally described by Epton (2). This is a twophase (chloroform and water) titration with a standard sodium lauryl sulfate (SLS) solution using a high pH (about 11) sodium carbonate buffer and a bromphenol blue indicator end point. Some operators have found the procedure difficult for control purposes. Moreover, chloroform has been classified as an industrial substance with suspected carcinogenic potential for humans by the American Council of Governmental Industrial Hygienists (3). Metcalfe et al. (4) titrated quats with tetraphenyl boron (TPB) using dichlorofluoroscein as a visual indicator. Wang et al. (5) improved Metcalfe's method by titrating with TPB potentiometrically using platinum-platinum electrodes.In ASTM method D-4251-89 (6), anio...

Titrimetric methods for determining cationic surfactants

“…To determine the endpoint, standard sodium lauryl sulfate was chosen as a titrant, and a nitrate-ionselective or surface-active electrode was used. A comparison of the results of these two methods showed that the automatic potentiometric method is more accurate, simpler, faster and, in general, more suitable for use in production laboratories than the biphasic titration method [64].…”

Detection and antimicrobial activity of immobilized quaternary ammonium antimicrobial monolayers on porous and non-porous surfaces

“…A variety of titration methods employing organic dyes were developed to quantify the amount of quaternary ammonium salts widely employed as antimicrobials in consumer products and pesticides in waste H 2 O. 174,175 The most popular methods employ bromophenol blue and dichlorofluorescein as dyes capable of binding to the quaternary ammonium through an ion pair interaction. Biphasic titrations employed bromphenol blue (Figure 1.51, 1.53) whereas dichlorofluorescein was used in a monophasic titration to determine QAS directly (Figure 1.52).…”

Self-Assembling Quaternary Ammonium Sulfonamide Antimicrobials

“…Over the years, various titration, colorimetric and LC -GC spectrum methods using dyes have been employed to quantify the amount of QUAT present in consumer products and waste water. 76 The most commonly used qualitative method involves a water soluble bromophenol The bromophenol blue dye complexes with the surface bound QUAT resulting in a blue stain. Once complexed, the material is permanently stained, damaged and unusable.…”