Selective and eco-friendly method for determination of mercury(II) ions in aqueous samples using an on-line AuNPs–PDMS composite microfluidic device/ICP-MS system

In this study we developed an on-line, eco-friendly, and highly selective method using a gold nanoparticle (AuNP)-coated polydimethylsiloxane (PDMS) composite microfluidic (MF) chip coupled to inductively coupled plasma mass spectrometry (ICP-MS) to separate trace Hg2+ ions from aqueous samples. Because Hg2+ ions interact with AuNPs to form Hg–Au complexes, we were able to separate Hg2+ ions from aqueous samples. We prepared the AuNPs–PDMS composite through in situ synthesis using a PDMS cross-linking agent to both reduce and embed AuNPs onto PDMS microchannels so that no additional reductants were required for either AuNP synthesis or the PDMS surface modification (2% HAuCl4, room temperature, 48 h). To optimize the proposed on-line system, we investigated several factors that influenced the separation of Hg2+ ions in the AuNPs–PDMS/MF, including adsorption pH, adsorption and elution flow rates, microchannel length, and interferences from coexisting ions. Under optimized conditions (pH 6.0; adsorption/elution flow rates: 0.05/0.5 mL min–1; channel length: 840 mm), we evaluated the accuracy of the system using a standard addition method; the measured values had agreements of ≥93.0% with certified values obtained for Hg2+ ions. The relative standard deviations of the proposed method ranged from 2.24% to 6.21%. The limit of detection for Hg2+ for the proposed on-line AuNPs–PDMS/MF/ICP-MS analytical method was as low as 0.07 µg L−1.