Pressure-driven mesofluidic platform integrating automated on-chip renewable micro-solid-phase extraction for ultrasensitive determination of waterborne inorganic mercury

Abstract

A dedicated pressure-driven mesofluidic platform incorporating on-chip sample clean-up and analyte preconcentration is herein reported for expedient determination of trace level concentrations of waterborne inorganic mercury. Capitalizing upon the Lab-on-a-Valve (LOV) concept, the mesofluidic device integrates on-chip micro-solid phase extraction (μSPE) in automatic disposable mode followed by chemical vapor generation and gas–liquid separation prior to in-line atomic fluorescence spectrometric detection. In contrast to prevailing chelating sorbents for Hg(II), bare poly(divinylbenzene-N-vinylpyrrolidone) copolymer sorptive beads were resorted to efficient uptake of Hg(II) in hydrochloric acid milieu (pH=2.3) without the need for metal derivatization nor pH adjustment of prior acidified water samples for preservation to near-neutral conditions. Experimental variables influencing the sorptive uptake and retrieval of target species and the evolvement of elemental mercury within the miniaturized integrated reaction chamber/gas–liquid separator were investigated in detail.

Using merely <10 mg of sorbent, the limits of detection and quantification at the 3sblank and 10sblank levels, respectively, for a sample volume of 3 mL were 12 and 42 ng L−1 Hg(II) with a dynamic range extending up to 5.0 μg L−1. The proposed mesofluidic platform copes with the requirements of regulatory bodies (US-EPA, WHO, EU-Commission) for drinking water quality and surface waters that endorse maximum allowed concentrations of mercury spanning from 0.07 to 6.0 μg L−1. Demonstrated with the analysis of aqueous samples of varying matrix complexity, the LOV approach afforded reliable results with relative recoveries of 86–107% and intermediate precision down to 9% in the renewable μSPE format.

Highlights ► Mesofluidic pressure-driven platform for automatic on-chip μSPE. ► Bead injection in a Lab-on-a-Valve platform for determination of waterborne Hg(II). ► Selective retention of Hg(II) in hydrochloric acid onto bare Oasis HLB® copolymer. ► Determination of Hg(II) at levels below maximum allowed concentrations in waters.