Further studies on application of Al(III)-tetraazaporphine in membrane-based electrochemical sensors for determination of fluoride

Herein, fluoride-selective electrodes with polymer membranes doped with Al(III)-complex of tetraazaporphine (AlTAP) were thoroughly tested for possibility of use for determination of fluoride in samples of relatively low F− level, such as municipal water. For this aim electrodes with plasticized membranes containing AlTAP and both: unmodified poly(vinyl chloride) and borate additives or carboxylated PVC of various levels of functional groups were prepared and examined. For better characterization of tested ionophore prepared membranes were plasticized with bis(2-ethylhexyl) sebacate (DOS), o-nitrophenyl octyl ether (o-NPOE), 2-fluorophenyl 2-nitrophenyl ether (2-FPNPE) and chloroparaffin (CP).It was found that the reduction of examined sample pH from 3.0 to 2.2 allows for lowering of detection limit to levels, which are typically achieved when using LaF3-based electrode. Among tested, electrodes with membranes containing borate sites characterized themselves with slightly better detection limits and shorter response time. Optimization of measuring conditions allowed the determination of fluoride with good accuracy in municipal and mineral water samples.Moreover, in the framework of presented work, pulsed chronopotentiometry was tested in terms of elimination or limitation of OH− influence on detection limits of AlTAP-based sensors. It turned out, that chemical nature of hydroxide does not enable elimination of its influence on AlTAP-based sensors operation. Therefore, the lower detection limits obtained for sensors when using this technique were highly dependent on pH.