lead-selective neutral carriers in liquid membrane electrodes. Lead was detected as a ... Carrier mediated transport of cations was studied in a coaxial cell in ...
Sensors and Actuators B, 18-19 (1994) 383-386
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PbOH+ -selective membrane electrode based on crown ethers Wolfgang Hasse, Benedikt Ahlers, Jorg Reinbold and Karl Cammann Institute of Chemical and Biochemical Sensor Research, Westfiilische Wilhelms-Universitiit Manster, Chair of Analytical Chemistry, Wilhelm-Kiemm-Strasse 8, D-48149 Munster (Germany)
Abstract Crown ethers have often been reported as potential ionophores in alkali ion-selective electrodes. Several new lipophilic lariat crown ethers possessing a variety of single and double side alkyl ann(s) were found to act as lead-selective neutral carriers in liquid membrane electrodes. Lead was detected as a monovalent permeating species of the type PbOH+. The obtained analytically relevant lead sensors show a high selectivity with regards to other heavy metal ions, low detection limits ranging between 10- 6 and 10~7 molll and short response times.
Introduction Macrocyclic compounds are applied as ionophores in ion-selective electrodes widely used in analytical medicinelbiochemistry, environmental pollution monitoring etc. Crown ethers as ionophores with defined cavities, which have alkali-ion complexation properties and even sensitivities for Pb2+, have been well documented in the literature [1, 2]. Investigations on PVC-based membranes with new crown ethers 1-16 as neutral ionophores showed a considerably higher response to lead than to alkali ions. This paper deals with the preparation of a series of lariat crown ethers as carriers in electrodes and with investigations of the effect of structure on their properties in polymeric membranes with respect to lead ions. Due to the association of Pb 2 + with hydroxy anions the pH dependence of e.mJ. measurements was examined.
Experimental
solution I membrane II internal electrolyte 10- 2 M KCI, saturated with PbCl2 and AgCl at 10 °C; AgCl; Ag. Potentiometric selectivity coefficients KPb-M were determined by the separate solution method using 10- 2 M solutions of metal nitrates. The pH was adjusted by the addition of 0.1 M HN03 and Ca(OHh, respectively.
Transport experiments Carrier mediated transport of cations was studied in a coaxial cell in which two aqueous (receiving/source) phases are separated by a stirred chloroform membrane phase containing the carrier (5 X 10- 3 M). As a reference experiment (blank) transport without a carrier was carried out. The aqueous source phase consisted of a 0.1 M Pb(N03 h, the receiving phase was deionized water.
Carriers
Membranes The ion-selective membranes consisted of almost 1% wt./wt. of carrier dissolved in 33% wt./wt. PVC and 66% wt./wt. plasticizer (dibutylsebacate = DBS). Potentiometric measurements All measurements were carried out with cells of the following type: Ag; AgCl; 3 M KCl; 0.1 M LiAc Isample
