Sequential determination of lead and cobalt in tap water and foods samples by fluorescence

In this work, a new procedure was developed for the separation and preconcentration of lead(II) and cobalt(II) in several water and foods samples. Complexes of metal ions with 8-hydroxyquinolein (8-HQ) were formed in aqueous solution. The proposed methodology is based on the preconcentration/separation of Pb(II) by solid-phase extraction using paper filter, followed by spectrofluorimetric determination of both metals, on the solid support and the filtered aqueous solution, respectively. The solid surface fluorescence determination was carried out at lambda(em)=455 nm (lambda(ex)=385 nm) for Pb(II)-8-HQ complex and the fluorescence of Co(II)-8-HQ was determined in aqueous solution using lambda(em)=355 nm (lambda(ex)=225 nm). The calibration graphs are linear in the range 0.14-8.03 x 10(4) mu g L-1 and 7.3 x 10(-2)- 4.12 x 10(3) mu g L-1, for Pb(II) and Co(II), respectively, with a detection limit of 43 x 10(-2) and 2.19 x 10(-2) mu g L-1 (S/N=3). The developed methodology showed good sensitivity and adequate selectivity and it was successfully applied to the determination of trace amounts of lead and cobalt in tap waters belonging of different regions of Argentina and foods samples (milk powder, express coffee, cocoa powder) with satisfactory results. The new methodology was validated by electrothermal atomic absorption spectroscopy with adequate agreement. The proposed methodology represents a novel application of fluorescence to Pb(II) and Co(II) quantification with sensitivity and accuracy similar to atomic spectroscopies. (C) 2014 Elsevier B.V. All rights reserved.