Paraquat sensors containing membrane components of high lipophilicities

In the first part of this paper, the development of high-performance paraquat selective potentiometric sensors based on octamethylcyclotetrasiloxane is described. In the fabrication of these sensors, the use of highly lipophilic PVC-based membrane components, namely, plasticizer and anionic sites, is emphasized. The electrochemical characteristics of such sensors were evaluated and compared with earlier paraquat ion-selective electrodes (ISEs) that were based on the same sensing compound but with nitrophenyl octyl ether (NPOE) as plasticizing solvent and also based on dibenzo-30-crown-10. The use of bis(1-butylpentyl)decane-1,1-diyldiglutarate (BBDG) and tetra-n-undecyl 3,3′,4,4′-benzophenone tetracarboxilate (TBT) as plasticizer in conjunction with either sodium tetrakis[3,5-bis(trifluoromethyl)phenyllborate (NTB) or potassium tetrakis(4-chlorophenyl) borate (KTPB) as membrane additives all yielded functional paraquat selective chemical sensors of Nernstian slopes. Although the selectivity profile of these electrodes were slightly inferior as compared to a similar membrane system that uses NPOE as a plasticizer but was better than the earlier reported paraquat ISEs based on dibenzo-30-crown-10. A distinct advantage of the paraquat sensors described here was their resistance to fouling by surfactants as compared to earlier sensors that used NPOE as a plasticizer. The second part of this paper deals with the usage of the promising membrane systems described above when applied on the surface of platinum wire and subsequently used as a flow-through potentiometric detector. A brief description of the flow-through detector design and optimization of the flow-injection analysis (FIA) set-up were also presented. Analysis of 0.01–0.l mM paraquat dichloride in backgrounds of well, river and lake waters when performed in the FIA mode gave excellent recoveries. A throughput of 85 samples h−1 can be achieved with this system.