Measuring quaternary ammonium cleaning agents with ion selective electrodes

• Published in: Analytica chimica acta 2006-06, Vol.570 (2), p.186-194
• Main Authors: Plesha, Michael A., Van Wie, Bernard J., Mullin, James M., Kidwell, David A.
• Format: Article
• Language: English
• Subjects: Analytical chemistry; Chemistry; Electrochemical methods; Exact sciences and technology; Ion selective electrode; Polymeric reference electrode; Quaternary ammonium ion; Selectivity; Surfactant
• ISSN: 0003-2670; 1873-4324
• DOI: 10.1016/j.aca.2006.04.024

Data for coated-wire, ion selective electrodes (ISEs) are presented for cationic surfactant ions found in common cleaners including benzyldimethyltetradecylammonium, benzyldimethyldodecylammonium, and benzyldimethylhexadecylammonium. The ion exchangers dinonylnaphthalene sulfonic acid, tetraphenyborate, and tetrakis(4-chlorophenyl)borate are examined, showing dinonylnaphthalene sulfonic acid to be the favored species. The ISEs exhibit approximately Nernstian behavior down to the 10 −6 M limit of detection with lifetimes in excess of 50 days when used continuously, and a shelf life of over 100 days. Reaching the upper detection limit at the critical micelle concentration requires use of polymeric-membrane reference electrodes including a new membrane cocktail, which allow response measurements of an order of magnitude higher than the traditional fritted-glass reference electrode. The surfactant ISEs show excellent selectivity over the common metal ions Na +, K +, Mg 2+, Ca 2+, and Cu 2+ with selectivity coefficients less than 10 −5.3. The ISEs are also selective over the lower molecular weight quaternary ammonium ions tetradecyltrimethylammonium, dodecyltrimethylammonium, benzyldimethyl(2-hydroxyethyl)ammonium, and tetrabutylammonium with selectivity coefficients ranging from 10 −1.7 to 10 −5.5. Use of a single electrode to determine accurately the total cationic surfactant concentration in common cleaning solutions is accomplished with information about concentration dependent interferences and a modified Nikolsky–Eisenman model. Finally, quaternary ammonium surfactants have a deleterious effect on the measurements of pH and common ions like K +, Mg 2+ and Ca 2+ with polymeric ISEs. This makes it critical to include surfactant electrodes in a detector array when cleaning agents are present.