Separation of alkanes in Citrus essential oils by on-line coupled high-performance liquid chromatography-high-resolution gas chromatography

Abstract

The development of gas chromatography (GC) and especially high-resolution GC (HRGC) has made it possible to study essential oils in depth. The high resolving power of capillary columns has allowed separations of the many components present, but the great complexity of the matrices often requires the use of different stationary phases and the use of mass spectrometry (MS) in order to identify the components accurately. Sometimes not even MS is able to identify all the components because similar components give similar fractionation patterns, e.g., as happens with sesquiterpenes’. The recently developed coupling of high-performance liquid chromatography (HPLC) with HRGC has been a great help towards improving our knowledge of the composition of essential oils ‘g3 because it is possible to use simultaneously the high , separating power of HPLC and HRGC to separate the numerous components which are present. The components are first separated by HPLC into relatively small volume of eluate which can be introduced on-line into the gas chromatograph, thus avoiding too much handling of the sample, which can lead to errors. The alkanes in Citrus essential oils have not been studied much up to now4-‘. On-line HPLC-HRGC with concurrent solvent evaporation’-” has been used in our research to study the alkane fraction of cold-pressed Citrus essential oils. The HPLC eluate is injected into the gas chromalograph by using the concurrent solvent evaporation technique. The temperature of the GC column is maintained at a higher value than boiling point of the HPLC eluent, taking into account both the composition of the eluent and the inlet pressure of carrier gas”*r2.