Quantitative determination of 2-and 4-methylimidazole in soy sauce using dispersive solid phase extraction and ultra-high performance liquid chromatography-tandem mass spectrometry.

Objective To establish a simple and rapid method for determination of 2-methylimidazole(2-MID) and 4-methylimidazole(4-MID) in soy sauce using dispersive solid phase extraction(dSPE) clean-up and ultra-high performance liquid chromatography-tandem mass spectrometry(UPLC-MS/MS). Methods The isotope internal standard was added into the samples, which then was diluted with water and adjusted to alkaline, processed by liquid-liquid extraction with acetonitrile, followed by adding anhydrous MgSO4 and anhydrous NaAC. Then the extract of dark soy sauce was purified by primary secondary amine(PSA) sorbent plus multi-walled carbon nanotubes(MWNTs). The ultimate solution was separation with UPLC BEH HILIC(50 mm×2.1 mm, 1.7 μm), elution with acetonitrile and 10 mmol/L ammonium acetate(containing0.1% formic acid, v/v), and detection with tandem mass spectrometry under ESI at positive and multiple reaction monitoring(MRM) mode. The targets were quantified by isotope internal standard. Results The limit of detection(LOD) of the MIDs were both 1.5 μg/kg, and the linear range were 1.0~100 μg/L with the correlation coefficients larger than 0.999. The average recoveries ranged from 89.6% to 117.2%, and within-day precisions were in a range of 4.8%~12.9% when three levels of standard were spiked into light and dark soy sauce. The inter-day precisions were less than 15%. Conclusion The developed method is simple, rapid, accurate and sensitive for the detection of 2-MID and 4-MID in soy souse.