Abstract: A method for the determination of mineral oil saturated hydrocarbons (MOSH) and mineral oil aromatic hydrocarbons (MOAH) in chocolate was established using on-line liquid chromatography-gas chromatography (LC-GC). Samples were extracted with n-hexane while sonicating at 60 ℃ for 20 min, and the collected supernatant was treated with silica gel for lipid removal. Then epoxidation was employed with m-chloroperoxybenzoic acid in order to oxidize the endogenic olefins in samples. Finally, the separation and determination were conducted by LC-GC, in which LC was used to retain both oil and olefin epoxide, and the isolated MOSH and MOAH were separately introduced into the two parallel GC channels through the LC-GC interface consisting of transferring valves, retention gaps and solvent release valves and detected with a flame ionization detector. The calibration curves for MOSH and MOAH were linear in the range of 0.5–85.5 mg/L (R2 = 0.998), and the limit of quantification (LOQ) of the method was 0.5 mg/kg. The spiked recoveries were in the range of 80.3%–93.8% with relative standard deviation (RSD) of 1.58%–8.22%. This method was used to determine the mineral oil in 28 commercial chocolate products, of which 20 samples were found to contain MOSH in the range of 1.83–22.23 mg/kg and 1 sample was found to contain MOAH at 1.57 mg/kg. The analysis of on-line LC-GC chromatograms demonstrated that some chocolate products contained polyolefin oligomeric saturated hydrocarbons (POSH) migrating out from plastic packages. POSH and MOSH could not be separated from each other by on-line LC-GC, so the measured results were actually the total amount of MOSH and POSH.

Key words: chocolate; mineral oil saturated hydrocarbons; mineral oil aromatic hydrocarbons; on-line liquid chromatography-gas chromatography; epoxidation