PVC matrix membrane sensor for potentiometric determination of cetylpyridinium chloride

A novel cetylpyridinium chloride-selective membrane sensor consisting of ce tylpyridinium-ferric thiocyanate ion pairs dispersed in a PVC matrix placti cized with dioctylphthalate is described. The electrode shows a stable, nea r-Nernstian response for 1 x 10(-3) - 1 x 10(-6) mol l(-1) cetylpyridinium chloride (CPC) at 25 degreesC over the pH range 1 - 6 with a cationic slope of 57.5 +/- 0.4. The lower detection limit is 8 x 10(-7) mol l(-1) and the response time is 30 - 60 s. Selectivity coefficients for CPC relative to a number of interfering substances were investigated. There is negligible in terference from many cations, anions and pharmaceutical excipients; however , cetyltrimethylammonim bromide (CTMAB) interfered significantly. The deter mination of 0.5 - 350 mug/ml of CPC in aqueous solutions shows an average r ecovery of 98.5% and a mean relative standard deviation of 1.6% at 56.0 mug /ml. The direct determination of CPC in Ezafluor mouthwash gave results tha t compare favorably with those obtained by the British Pharmacopoeia method . Precipitation titrations involving CPC as titrant are monitored with a CP sensor. The CP electrode has been utilized as an end point indicator elect rode for the determination of anionic surfactants in some commercial deterg ents.