Determination of mineral oil hydrocarbon contamination in Citrus essential oils by using on-line liquid-gas chromatography: critical aspects

The present manuscript reports and discusses critical issues related to the determination of mineral oil hydrocarbon contamination in Citrus essential oils (EOs); an on-line liquid-gas chromatography system equipped with a Y-interface was used (with no additional off-line step for pre-concentration). In total, eighteen samples were analyzed, specifically eleven cold-pressed (CP) and seven distilled EOs. With regard to the CP EOs, various degrees of mineral oil saturated hydrocarbon (MOSH) contamination were detected, ranging between 10.7 and 338.4 mg kg(-1) (only one sample was MOSH-free); different MOSH sub-fractions were determined, with the > C-25- = C-35 sub-fraction always present, with an average concentration of 74.5 mg kg(-1). Based on the EO composition, different sample amounts were injected to avoid the overloading of the LC column and consequently the GC one, thus leading to different limits of quantification (LoQ), which were either 2 mg kg(-1) (for bergamot EO) or 5 mg kg(-1) (for all the other investigated samples). For all samples, the mineral oil aromatic hydrocarbon level was always lower than the LoQ.

Automated summary

This study analyzed and discussed the contamination of mineral oil hydrocarbons in Citrus essential oils using an online liquid-gas chromatography system. Various degrees of mineral oil saturated hydrocarbon (MOSH) contamination were found in the cold-pressed (CP) essential oils, ranging from 10.7 to 338.4 mg kg(-1). However, no MOSH contamination was detected in the distilled essential oils. The level of mineral oil aromatic hydrocarbons in all samples was below the limit of quantification.