Lead(II) ion selective electrodes with PVC membranes based on two bis-thioureas as ionophores: 1,3-bis(N′-benzoylthioureido)benzene and 1,3-bis(N′-furoylthioureido)benzene

Abstract

Two PVC membrane ion selective electrodes for Pb(II) ion based on two bis-thioureas: 1,3-bis(N′-benzoylthioureido)benzene and 1,3-bis(N′-furoylthioureido)benzene as ionophores, are reported. A first membrane formulated using 1,3-bis(N′-benzoylthioureido)benzene as carrier exhibited a Nernstian response to Pb(II) over a wide concentration range (4.0 × 10 −6 to 1.0 × 10 −2 M) with a slope of 31.5 ± 1.6 mV/dec. It showed a fast response time ( t 90% = 14 s) and could be used for 10 weeks without any divergence in potentials. The membrane formulated using 1,3-bis(N′-furoylthioureido)benzene as carrier exhibited a Nernstian response in the concentration range (5.0 × 10 −6 to 1.0 × 10 −2 M), with a slope of 30.0 ± 1.3 mV/dec. Its response time was t 90% = 14 s, and it could be used for 14 weeks without any divergence in potentials. The two proposed potentiometric sensors revealed acceptable selectivities for Pb(II) over a wide variety of other metal ions and could be used in a pH range of 2.2–6.0. Both electrodes were assayed in direct potentiometric determination of lead in soils (10–30 mg/kg range) with very good performance (0.99935 correlation coefficient in the comparison against ICP-MS method).