Determination of Sodium Dodecyl Sulfate in Toothpastes by a PVC Matrix Membrane Sensor

The construction and characteristic performance of a new potentiometric PVC membrane sensor responsive for sodium dodecyl sulfate (SDS) are described. The sensor is based on the use of cetyltrimethylammonium-tetraphenylborate (CTA-TPB) ion-pair complex as electroactive material in PVC matrix in presence of dioctyl phthalate as a solvent mediator. The sensor exhibits a rapid, stable and near-Nernstian response for SDS over the concentration range of 5 x 10(-3)-5 x 10(-6) mol dm(-3) at 25 +/- A 2 A degrees C and the pH range 4-8.5 with slope of 59.6 mV/decade change in SDS concentration. The lower detection limit is 5 x 10(-6) mol dm(-3) and the response time is 45 s. The determination of selectivity coefficients for different anions shows there is no interference except that of dodecyl benzene sulfonate (DBS-) ion which has a strong interference. The results obtained in the determination of SDS in toothpastes, using this sensor as an indicator electrode, were compared with those obtained from the spectrophotometric method using methylene blue as the reagent.