Lead-selective membrane electrode based on dibenzyl phosphate

Lead-selective poly(vinyl chloride) electrodes based on some synthesized benzo-substituted macrocyclic diamides

A series of recently synthesized benzo- and pyridine-substituted macrocyclic diamides were studied to characterize their abilities as lead ion carriers in PVC membrane electrodes. The electrode based on 3,15,21-triaza-4,5;13,14-dibenzo-6,9,12-trioxabicycloheneicosa-1,17,19-triene-2,16-dione exhibits a Nernstian response for Pb2+ ions over a wide concentration range (1.3 x 10(-2) to 3.6 x 10(-6) mol L(-1)) with a limit of detection of 2.0 x 10(-6) mol L(-1) (0.4 ppm). The response time of the sensor is approximately 16 s, and the membrane can be used for more than two months without observing any deviation. The electrode revealed comparatively good selectivities with respect to many cations including alkali earth, transition and heavy metal ions. The proposed sensor could be used in pH range of 3.7-6.5. It was used as an indicator electrode in potentiometric titration of chromate ions with a lead ion solution.

Developments in the Field of Conducting and Non-conducting Polymer Based Potentiometric Membrane Sensors for Ions Over the Past Decade

Many research studies have been conducted on the use of conjugated polymers in the construction of chemical sensors including potentiometric, conductometric and amperometric sensors or biosensors over the last decade. The induction of conductivity on conjugated polymers by treating them with suitable oxidizing agents won Heeger, MacDiarmid and Shirakawa the 2000 Nobel Prize in Chemistry. Common conjugated polymers are poly(acetylene)s, poly(pyrrole)s, poly(thiophene)s, poly(terthiophene)s, poly(aniline)s, poly(fluorine)s, poly(3-alkylthiophene)s, polytetrathiafulvalenes, polynapthalenes, poly(p-phenylene sulfide), poly(p-phenylenevinylene)s, poly(3,4-ethylenedioxythiophene), polyparaphenylene, polyazulene, polyparaphenylene sulfide, polycarbazole and polydiaminonaphthalene. More than 60 sensors for inorganic cations and anions with different characteristics based on conducting polymers have been reported. There have also been reports on the application of non-conducting polymers (nCPs), i.e. PVC, in the construction of potentiometric membrane sensors for determination of more than 60 inorganic cations and anions. However, the leakage of ionophores from the membranes based on these polymers leads to relatively lower life times. In this article, we try to give an overview of Solid-Contact ISE (SCISE), Single-Piece ISE (SPISE), Conducting Polymer (CP)-Based, and also non-conducting polymer PVC-based ISEs for various ions which their difference is in the way of the polymer used with selective membrane. In SCISEs and SPISEs, the plasticized PVC containing the ionophore and ionic additives govern the selectivity behavior of the electrode and the conducting polymer is responsible of ion-to-electron transducer. However, in CPISEs, the conducting polymer layer is doped with a suitable ionophore which enhances the ion selectivity of the CP while its redox response has to be suppressed.