Optimization, evaluation, and characterization of a hollow fiber supported liquid membrane for sampling and speciation of lead(II) from aqueous solutions

Hollow fiber supported liquid membrane sampling and speciation of lead(II) from aqueous solution using a selective carrier (Kelex 100) is studied. An optimization of different variables affecting permeation performance (chemical conditions of the sampling module - pH, concentration and nature of the acceptor phase, extractant concentration; membrane impregnation form; sampling time; and hollow fiber length) and an evaluation of those that influence the performance of the device under sampling conditions (sample pH; interfering cations - Cu(II), Cr (VI), Co(II), Cd(II), Ni(II), and Zn(II); anions - NO2-, SO42-, Cl-, NO3-, CO32-, CN- -, and organic matter - humic acids; lead concentration; and sample temperature) are reported. Kelex 100 concentration within the range 12-47 mmol dm(-3), acceptor solution pH 2.2, hollow fiber length within the range 15-100 cm, and impregnation using mode III were found as optimal conditions for operation of the device. A linear equation described well the dependency of enrichment factor on sample pH in the 5.7-7.0 interval, the presence of 1 x 10(-6) mol dm-3 of Cu(II), Cr(VI), Co(11), Cd(11), Ni(II), or Zn(II) did not interfere in Pb(II) enrichment factor, 50 mg dm-3 of anions capable of forming labile complexes (NO2-, SO42-, Cl-, NO3-, CO32-) and 5 mg dm(-3) of CN- produced a catalyzing effect in the permeation rate, which increased as lead concentration diminished. The presence of strong humic acid inert complexes in the donor phase caused a reduction in the enrichment factor, which additionally increases linearly as temperature increases. The possibilities for using the hollow fiber device for lead speciation in terms of permeation of free and labile species and rejection of inert complexes are discussed on the basis of such analyses. Composition-performance relationships for sampling module characterization and evaluation are analyzed as well. (C) 2010 Elsevier B.V. All rights reserved.