Ag-Solid-Phase Extraction-Programmed Temperature Vaporization-Gas Chromatography for Analysis of Mineral Oil-Saturated Hydrocarbons in Commercial Chocolates / 分析化学

ABSTRACT

An offline silver-impregnated silica gel solid-phase extraction (Ag-SPE) approach combined with a programmed temperature vaporization-gas chromatography-flame ionization detector (PTV-GC-FID) was proposed for routine analysis of mineral oil saturated hydrocarbons (MOSH) in chocolates. The MOSH in chocolates were extracted by n-hexane and 1 mL of extract was purified by offline Ag-SPE column. The SPE columns packed with 0.3％ Ag-activated silica gel were used to separate MOSH from triglycerides and olefins in chocolates. The eluent of MOSH fraction was only 5 mL and then concentrated to 0.2 mL through nitrogen blowing with little evaporation loss. The PTV parameters were as follows: the initial temperature was set at 45℃ and held for 1 min (split ratio was 200∶1), then warmed up to 360℃ at linear gradient of 250℃ minSymbolm_1 and held for 27 min (split valve was closed for 2 min followed by split ratio of 100∶1). The GC injection volume was 40 μL. The GC column was heated from 35℃ (3 min) to 350℃ at 25℃/min, and then raised to 370℃ (10 min) at 5℃/min. The flow rate of the carrier gas was 1.3 mL/min (and pressure was 60 kPa), FID temperature was set at 380℃. The limit of quantification (LOQ) and the recoveries of the method were 0.5 mg/kg and 84.9％-108.6％, respectively, with the relative standard deviations (RSD) of 0.2％-1.5％. Twenty-five commercial chocolate samples were analyzed with the proposed method, and it was found that the MOSH in three samples were not detected, and the concentrations of MOSH in other 22 samples were 1.09-8.15 mg/kg (the concentrations of MOSH with C16-C35 component were 0.56-4.43 mg/kg). The results suggested that it was necessary to routinely detect mineral oil contamination in chocolates for food safety.