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

•A compact point dischage microplasma optical emission spectrometry was fabricated by 3D printing for speciation analysis of mercury.•Total mercury (IHg and MeHg) and IHg were selectively reduced to Hg0 in the presence and the absence of the oxidant KMnO4.•The limits of detection (LODs) were found to be 0.1 μg L−1 for both IHg and MeHg and the relative standard deviations (RSDs) (n = 11) were better than 4.3%.•The propose method was applied for the rapid and on-site safety assessment of fish oil and its relevant dietary supplements.