Cetyltrimethylammonium-selective PVC electrode based on its trinitrobenzene sulfonate ion-pair

A PVC membrane electrode selective for cetyltrimethylammonium ion was prepa red. The active element is a plasticized polyvinyl chloride membrane contai ning a dissolved ion pair complex of CTAB with trinitrobenzene sulfonic aci d (TNBS). The electrode showed a near-Nernstian response within the CTA(+) concentration range from 1.08 x 10(-6) to 8 x 10(-4) M at 25 +/- 1 degrees C, good selectivity, precision (RSD=1.04%), and usable within the pH range 2.5-10.2. The isothermal temperature coefficient of the electrode amounted to -0.00007 V/degrees C. The electrode has been used for the direct determi nation of cetyltrimethylammonium bromide either by the standard addition me thod or by potentiometric titration against TNBS at pH 7.