Synthesis, characterisation and application of two new lariat crown ethers in construction of PVC membrane, coated wire and coated graphite electrodes: application to flow injection potentiometry

Abstract

Two lariat crown ethers, 7-(2-Hydroxy-5-methylbenzyl)-5,6,7,8,9,10-hexahydro-2H-benzo[b][1,4,7,10,13]pentadecine-3,11(4H,12H)dione, L1 and, (7-(5-tert-buthyl-2-hydroxybenzyl)-5,6,7,8,9,10-hexahydro-2H-benzo[b][1,4,7,10,13]dioatriazacyclopentadecine-3,11 (4h, 12, H) dione, L2 was synthesised, characterised and used as active components for fabrication of PVC membrane electrode (PME), coated graphite electrode (CGE) and coated wire electrodes (CWE) for sensing Co2+ ion. Potassium tetrakis(p-cholorophenyl) borate(KTpClPB) and o-nitrophenyloctyl ether (o-NPOE) were used as anion excluder and plasticiser, respectively, in a PVC matrix. The two lariat ethers were tested, L1 has shown better electrode characteristics than the other. The electrodes exhibited linear Nernstian responses to Co2+ ion in the linear concentration range of 3.3 × 10−6–1.9 × 10−2 M (for PME), 2.3 × 10−7–7.9 × 10−2 M (for CWE), and 5.0 × 10−8–1.2 × 10−2 M (for CGE). The CGE was used as a proper detection system in flow-injection potentiometry (FIP) with a linear Nernstian range of 2.3 × 10−7–1.2 × 10−2 M. Over a pH range of 3.2 to 8.0, the limit of detection for PME, CWE, CGE, and CGE-FIP systems were found to be 1.2 × 10−6, 2.5 × 10−7, 3.5 × 10−8 and 1.0 × 10−7 M, respectively. The electrodes revealed fairly good discriminating ability towards Co2+ in comparison with a large number of alkali, alkaline earth, transition and heavy metal ions. The electrodes were found to be chemically inert, showing fast response time of <5 s, and could be used practically over a period of 1 month. CGE has also been used for measurement of Co2+ in binary mixtures.