Separation and analysis of lipophilic extractives by hyphenated gas chromatography (GC-MS/FID)

Lipophilic plant extractives are typically obtained by extraction/maceration with organic solvents or supercritical fluids. They are complex mixtures of terpenes, fatty acid derivatives, and phenolics, which are both traditional and contemporary sources for bioactive compounds. To analyse their composition, chromatographic methods with high resolution are necessary, one of them being gas chromatography. Identification of the components is then based on mass spectrometric techniques or retention time.

The approach of gas chromatography hyphenated to mass spectrometer and flame ionization detector (GC-MS/FID) has been established as a reliable and robust work-horse method for qualitative analysis (by MS) and synchronized quantification (by FID) of the families of extractives found in lignocellulosic material. With the available high-temperature GC-MS/FID, apolar molecules can be analysed with several columns of different polarity. For more hydrophilic compounds, multiple optimized and validated derivatization techniques are available. As the system is optimized for high-temperature separations, molecules  up to and including triterpenes and triglycerides can be analysed, with or without derivatization beforehand. Identification of the individual compounds is achieved by Mass Spectrometry (single quadrupole) and by comparing the obtained fragment patterns with mass spectral libraries, both commercial and in-house. As orthogonal identifier, retention indices are used. Quantification can be based on the response of a Flame Ionization Detector – which is operated simultaneously during the same analysis – even if no analytical standard is available.2 Besides solid, liquid and oily samples, Solid Phase Microextraction is available to sample very volatile, small molecules from a sample’s headspace.

References:

1) Gutiérrez, A.; del Rı́o, J. C.; González-Vila, F. J.; Martı́n, F. Analysis of lipophilic extractives from wood and pitch deposits by solid-phase extraction and gas chromatography. J. Chromatogr. A 1998, 823(1), 449-455. doi.org/10.1016/S0021-9673(98)00356-2.

2) de Saint Laumer, J.-Y.; Leocata, S.; Tissot, E.; Baroux, L.; Kampf, D. M.; Merle, P.; Boschung, A.; Seyfried, M.; Chaintreau, A. Prediction of Response Factors for Gas Chromatography with Flame Ionization Detection: Algorithm Improvement, Extension to Silylated Compounds, and Application to the Quantification of Metabolites: Gas Chromatography. J. Separation Sci. 2015, 38(18), 3209–3217.

doi.org/10.1002/jssc.201500106.

3) Guggenberger, M.; Potthast, A.; Rosenau, T.; Böhmdorfer, S. Quantification of Volatiles from Technical Lignins by Multiple Headspace Sampling-Solid-Phase Microextraction-Gas Chromatography-Mass Spectrometry. ACS Sust. Chem. Eng. 2019, 7, 9896–9903. doi.org/10.1021/acssuschemeng.9b00630.