New Potentiometric Sensor for Determination of Low Levels of Anionic Surfactants in Industrial Effluents

The new surfactant sensor based on tetrahexadecylammonium dodecylsulfate as sensing ion-exchange complex, incorporated in plasticised PVC-membrane, has been used for potentiometric titration of low level anionic surfactants. The sensor exhibited near Nernstian response for dodecylsulfate (55.7 mV/decade) in the range 1.4·10−6 −5.6·10−3 mol/L and 57.3 mV/decade for dodecylbenzensulfonate in the range 1.9·10−6 −1.6·10−3 mol/L There are no significant interferences from organic and inorganic anions, commonly used in surfactant based industrial and household formulations at anionic surfactant potentiometric determination. The solutions of low levels (down to 10−5 mol/L) anionic surfactants (dodecylbenzensulfonate and dodecylsulfate) were successfully titrated with 1,3-didecyl-2-methylimidazolium chloride as standard cationic titrant. The sensor was used for determination of anionic surfactants in diluted industrial detergent products and industrial waste waters. The results obtained agree satisfactory with standard extraction-spectrophotometric MBAS method and are comparable with those obtained using a commercial surfactant electrode.

Potentiometric determination of cetylpyridinium chloride using a new type of screen-printed ion selective electrodes

A new type of screen-printed ion-selective electrode for the determination of cetylpyridinium chloride (CPC) is presented. These new electrodes involve in situ, modified and unmodified screen-printed ion-selective electrodes for the determination of CPC. The screen-printed electrodes (SPEs) show a stable, near-Nernstian response for 1 x 10(-2) to 1 x 10(-6) M CPC at 25 degrees C over the pH range 2-8 with cationic slope 60.66+/-1.10. The lower detection limit is found to be 8 x 10(-7) M and response time of about 3s and exhibit adequate shelf-life (6 months). The fabricated electrodes can be also successfully used in the potentiometric titration of CPC with sodium tetraphenylborate (NaTPB). The analytical performances of the SPEs are compared with those for carbon paste electrode (CPE) and polyvinyl chloride (PVC) electrodes. The method is applied for pharmaceutical preparations with a percentage recovery of 99.60% and R.S.D.=0.53. The frequently used CPC of analytical and technical grade as well as different water samples has been successfully titrated and the results obtained agreed with those obtained with commercial electrode and standard two-phase titration method. The sensitivity of the proposed method is comparable with the official method and ability of field measurements.

PVC matrix membrane sensor for potentiometric determination of cetylpyridinium chloride

A novel cetylpyridinium chloride-selective membrane sensor consisting of cetylpyridinium-ferric thiocyanate ion pairs dispersed in a PVC matrix placticized with dioctylphthalate is described. The electrode shows a stable, near-Nernstian response for 1 x 10(-3)-1 x 10(-6) mol l-1 cetylpyridinium chloride (CPC) at 25 degrees C 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 interference from many cations, anions and pharmaceutical excipients; however, cetyltrimethylammonim bromide (CTMAB) interfered significantly. The determination of 0.5-350 micrograms/ml of CPC in aqueous solutions shows an average recovery of 98.5% and a mean relative standard deviation of 1.6% at 56.0 micrograms/ml. The direct determination of CPC in Ezafluor mouthwash gave results that 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 electrode for the determination of anionic surfactants in some commercial detergents.