Construction of an anion-selective electrode: Dichromate-selective electrode

The construction, performance and application of dichromate-selective PVC membrane electrodes based on 5,11,17,23-tetra-tert-butyl-25,27,-bis-(isoniazidylcarbonylmethoxy)-26,28-dihydroxycalix[4]arene are reported in this study. An optimum membrane composition of 2% ionophore, 68.3 mol% plasticizer, 29.7 mol% PVC and 60 mol% lipophilic additive with respect to the ionophere is found for the proposed electrodes. The influences of the plasticizer, polimer, lipophilic additives, pH of test solutions, internal filling solutions and thickness of membrane on the potentiometric response of electrodes are investigated. The electrode exhibits linear response of the dichromate ions in the concentration range of 1.0 × 10−1 to 1.0 × 10−7 M with 4.3 × 10−8 M detection limit at pH 1.0. The slope of the calibration curve is 41.5 ± 0.2 mV/decade. The proposed electrode shows good selectivity for dichromate ions in presence of some metal cations and anions. The electrode has a response time about 15–20 s and it can be used at least for 14 months with good reproducibility and repeatibility. The redox titrations involving dichromate as a titrant are monitored with the sensor, and iron(II) in pharmaceutical preperations is determined.