A mesofluidic platform integrating restricted access-like sorptive microextraction as a front end to ICP-AES for the determination of trace level concentrations of lead and cadmium as contaminants in honey

Abstract

An automatic programmable-flow system capitalizing upon mesofluidic Lab-On-Valve (LOV) sample processing coupled on-line to inductively coupled plasma atomic emission spectrometry (ICP-AES) is proposed in this work as a quality control tool for expedient assessment of potential contamination episodes of food safety elements (namely, Cd and Pb) in a variety of undigested ripened honeys, taken as a model of an edible matrix. On-chip micro-solid phase extraction (μSPE) is effected in a bead-injection disposable sorbent mode using a cationic exchange restricted access-like material (viz., Bond Elut Plexa PCX). We have proven that the lifetime of the miniaturized solid reactor on-chip (11 ± 0.6 mg) is limited to processing less than 6 mL of unfiltered sample suspension (5% (w/w) honey buffered at pH 4.5) after which the analytical performance is severely deteriorated because of strong adherence of the sample matrix to the bead surface. Several physicochemical parameters including the nature of the sorbent material and its ionic form were investigated in detail so as to maximize absolute recoveries and enrichment factors of Pb and Cd. Variables for the elution process were explored by means of a full factorial design. Using 4.0 mL of sample and 200 μL of 3.0 mol L⁻¹ HNO₃ as an eluent, enrichment factors of ca. 15 with extraction/elution efficiencies close to 80% and relative recoveries ranging from 90–111% in honey were obtained for both Pb and Cd. The limits of detection (LODs), based on the 3s_intercept criterion, were 26 ng g⁻¹ and 68 ng g⁻¹ for Cd and Pb, respectively, which are far below those endorsed by current regulatory agencies (namely, 100 and 300–500 ng g⁻¹ for Cd and Pb, respectively). Demonstrated by the analysis of a suite of off-the-shelf honey brands, the proposed LOV-μSPE platform hyphenated to ICP-AES is deemed suitable for the reliable quantitation of trace level concentrations of Pb and Cd in honey and the detection of heavy metal contamination episodes.