Lead (II) Ion-Selective Membrane Electrodes Based on Four Nitrogen-Containing Heterocyclic Thioethers

Electrochemical performance of lead (II) ion-selective PVC membrane electrodes based on four nitrogen-containing heterocyclic thioethers L1∼L4 as the novel neutral ionophores is reported. Four ionophores are 1,4-bis(benzothiazol-2-ylthio)butane (L1), bis(benzothiazol-2-ylthio)methane (L2), bis(1,3,4-thiadiazol-2-ylthio)methane (L3), and 1,2-bis(1,3,4-thiadiazol-2-ylthio)ethane (L4). These electrodes are composed of bis(2-ethylhexyl) sebacate (DOS) as a plasticizer. The optimum electrodes based on L1∼L4 exhibited near-Nernstian or Nernstian response towards Pb²⁺ over a wide concentration range of 1.0 × 10⁻²∼5.0 × 10⁻⁶ M with the response slopes of 23.8, 30.2, 29.8, 29.6 mV/decade and the detection limits of 2.1 × 10⁻⁶, 1.0 × 10⁻⁶, 3.0 × 10⁻⁶, 3.6 × 10⁻⁶ M, respectively. Also, the sensors based on L1∼L3 and the electrode based on L4 have found to work satisfactorily in partially non-aqueous media up to 20% (v/v) or 50% (v/v) content of methanol, respectively. Good potential stability and reproducibility were observed for these sensors. The electrodes displayed good selectivity for lead ion over a number of alkali, alkaline earth and common transition metal ions. The practical analytical utility of the electrodes was demonstrated by measurement of Pb (II) in puffed food and the dust on the road, as well as potentiometric titration of lead ion with K₂CrO₄.