Direct coupling of liquid–liquid extraction with 3D-printed microplasma optical emission spectrometer for speciation analysis of mercury in fish oil

A simple method coupling liquid–liquid extraction (LLE) with 3D printed cold vapor generation point discharge microplasma optical emission spectrometry (CVG-µPD-OES) was constructed for the speciation analysis of mercury in fish oil. Mercury species contained in fish oil (mainly inorganic mercury (IHg) and methylmercury (MeHg)) were efficiently extracted into an aqueous medium containing 1.5% (m/v) L-Cysteine and 1% (m/v) ammonium acetate after a 3 min of vortex oscillation. Subsequently, the aqueous extracted solution was analyzed by CVG-µPD-OES. IHg was reduced to mercury cold vapor (Hg0) by the reaction with 0.02% (m/v) KBH4 in the absence of KMnO4, whereas total mercury (MeHg and IHg) could be converted to Hg0 by CVG after the pre-oxidation of KMnO4. All the generated Hg0 was separated from the condensed liquid phase and analyzed by µPD-OES. Under optimal experimental conditions, limits of detection (LODs) were found to be 0.1 μg L−1 for both MeHg and IHg, with relative standard deviations (RSDs, n = 11) of better than 4.3%. Two Certified Reference Materials (CRMs) and eight fish oils were analyzed to validate the accuracy and applicability with good recoveries (84%−114%). Since the 3D printing technique significantly decreases its instrument manufacturing difficulty and LLE improves its analytical performance, the LLE-CVG-µPD-OES featured portability, simplicity, low energy consumption, and high sensitivity, showing a promising prospect for the rapid and accurate safety assessment of fish oil and its relevant dietary supplements.