Hugues Brevard

Qualitative and quantitative analysis of vetiver essential oils by comprehensive two-dimensional gas chromatography and comprehensive two-dimensional gas chromatography/mass spectrometry.

Vetiver essential oils (VEO) are important raw ingredients used in perfume industry, entering the formula of numerous modern fragrances. Vetiver oils are considered to be among the most complex essential oils, resulting most of the time in highly coeluted chromatograms whatever the analytical technique. In this context, conventional gas chromatography has failed to provide a routine tool for the accurate qualitative and quantitative analysis of their constituents. Applying comprehensive two-dimensional gas chromatography techniques (GC×GC-FID/MS) afforded the mean to separate efficiently vetiver oil constituents in order to identify them in a more reliable way. Moreover, this is the first time that a complete true quantitation of each constituent is carried out on such complex oils by means of internal calibration. Finally, we have studied the influence of the injection mode on the determined chemical composition, and showed that several alcohols underwent dehydration under defined chromatographic conditions (splitless mode) usually recommended for quantitation purposes.

Identification of odor impact compounds of Tagetes minuta L. essential oil: comparison of two GC-olfactometry methods.

Odor impact compounds of Tagetes minuta L. essential oil were studied by gas chromatography (GC)-olfactometry using aroma extract dilution analysis (AEDA) and vocabulary-intensity-duration of elementary odors by sniffing (VIDEO-Sniff). AEDA was conducted by direct injection and revealed the presence of 43 odorant zones. Highest flavor dilution (FD) values were obtained for ethyl 2-methylpropanoate, ethyl 3-methylbutanoate, (E)-ocimenone, two tentatively identified thiols, and two yet unknown compounds. VIDEO-Sniff was realized by dynamic headspace sampling (D-HS) combined with 8W-GC-olfactometry where eight sniffers simultaneously detect volatile compounds obtained from a single chromatographic separation and revealed the presence of 42 odorant zones. Odorant trace compounds detected by GC-O that were present in quantities inferior to the GC-qMS systems detection limit and those subject to coelutions were identified by GC x GC-time-of-flight mass spectrometry (TOFMS). A total amount of 37 odorant components could be identified by VIDEO-Sniff, and the strong influence of the fruity notes of numerous esters stood out. Highest olfactory signals were obtained for ethyl 2-methylpropanoate, ethyl 2- and 3-methylbutanoate, and oct-1-en-3-one. Both methods hence come to the conclusion that ethyl 2-methylpropanoate and ethyl 2- and 3-methylbutanoate are among the main odorants in Tagetes minuta L. essential oil. Differences, advantages, and drawbacks of both GC-O methods are discussed.

Populus nigra L. bud absolute: a case study for a strategy of analysis of natural complex substances

AbstractThe new European regulations (e.g., REACH) require that Natural Complex Substances such as essential oils, absolutes, concretes, and resinoids are registered. This need implies that the chemical composition of these complex mixtures is characterized as exhaustively as possible in view of defining their toxicological risk. This study proposes an analysis strategy to be applied to the chemical characterization of poplar absolute as an example of Natural Complex Substances of vegetable origin. In the first part, the proposed strategy is described, and the advantages and the limitations related to the combination of conventional analytical techniques such as gas chromatography (GC) without and with sample derivatization and high-performance liquid chromatography (HPLC) are critically discussed. In the second part, the qualitative data obtained with GC and HPLC analysis of poplar bud absolute confirm the sample complexity which mainly consists of phenolic components. Fourteen compounds (i.e., phenolic acids, phenylpropanoids, and flavonoids) were then chosen as markers representative of the main classes of components characterizing poplar bud absolute. The marker quantitation carried out by GC-SIM-MS and HPLC-PDA analyses gives similar results confirming the reliability of both techniques. These results demonstrate that conventional analytical techniques can positively and effectively contribute to the study of the the composition of Natural Complex Substances, i.e., matrices for which highly effective separation is necessary, consisting mainly of isomers or homologous components. The combination of GC and HPLC techniques is ever more necessary for routine quality control when conventional instrumentations are used. FigureElucidation of Natural Complex Substances (NCS)

Characterization of volatile compounds of Indian cress absolute by GC-olfactometry/VIDEO-sniff and comprehensive two-dimensional gas chromatography.

Indian cress (Tropaeolum majus L.) has been consumed in salad or soup for decades, but its odors detailed molecular composition is still unknown. Here we report on the study of the odorant profile and odor-impact compounds of Indian cress absolute by GC-olfactometry/vocabulary-intensity-duration of elementary odors by sniffing (GC-O/VIDEO-Sniff) on an eight-way multiport system, combined with GCxGC-MS analyses for the identification of odorant trace constituents. Odor impact compounds of Indian cress absolute were determined by GC-O, and the overall influence of sulfury and fruity notes stood out. Forty-four odorant compounds were identified among which 22 (50% of the identified odorant molecules) were identified by using comprehensive two-dimensional GC coupled to a time-of-flight-mass spectrometer (TOFMS). These trace compounds were not detected by 1D-qMS or could only be found with specific searches once they were detected by comprehensive 2D-GC, although they were well perceived by the judges in GC-O. This was amongst others the case for the two molecules having the highest odor impact, (E)-hex-2-enal (fruity) and diethyl trisulfide (alliaceous, sulfury, cabbage). A powerful sulfur-containing odor compound whose first identification in cress was recently reported by the authors was detected by GC-O: O,S-diethyl thiocarbonate (fruity/red fruit and sulfury odor).

Unravelling the scent of vetiver: identification of character-impact compounds.

Vetiver oil is a highly esteemed basic ingredient of modern perfumery, but the nature of the constituents that really impart its typical and most sought woody‐earthy scent has remained controversial. Indeed, vetiver oil is considered as one of the most complex essential oils, being mostly composed of several hundreds of sesquiterpene derivatives with a large structural diversity. Its complexity has hindered the direct identification of its odoriferous components. We thus aimed at using a combination of GC×GC/MS and GC‐Olfactometry in order to identify most of its odor‐impact constituents. The olfactory analysis of vetiver oil and vetiveryl acetate revealed a huge variety of odors in both products. While khusimone has almost unanimously been recognized as the most characteristic vetiver odorant, we have identified several even more important contributors to the typical vetiver character.

StructureOdor Relationships of Semisynthetic β-Santalol Analogs

A series of eleven β‐santalol analogs, including nine new derivatives, was prepared by semisynthesis from natural (−)‐(Z)‐β‐santalol and studied by gas chromatography‐olfactometry (GC‐O) to characterize their olfactory properties and potencies. These compounds and 45 others selected in the literature were used to build three olfactophores by molecular modelling. Three models were obtained that gather structural and physicochemical constraints that will be useful for further design of new sandalwood odorants.

First Identification of O,S-Diethyl Thiocarbonate in Indian Cress Absolute and Odor Evaluation of Its Synthesized Homologues by GC-Sniffing

Indian cress (Tropaeolum majus L.) absolute was studied by GC-olfactometry (VIDEO-Sniff method) in order to identify odor-active aroma compounds. Because of its fruity-sulfury odor note, a compound that has never been identified in plant extracts before stood out: O,S-diethyl thiocarbonate, present at 0.1% (percentage of the total GC/FID area) in the extract. GCxGC-TOFMS allowed for a clean mass spectrum to be obtained, and isolation by preparative GC followed by NMR studies allowed its identification. Here, we report on the first detection of O,S-diethyl thiocarbonate in Indian cress absolute by GC-olfactometry/VIDEO-Sniff and on its isolation and identification. The synthesis and odor evaluation of its homologues are presented.

Towards a complete characterisation of guaiacwood oil

Guaiacwood oil is a common perfume ingredient used in modern compositions for its suave woody-rosy scent. This essential oil is a byproduct of the timber industry obtained by hydrodistillation of the heartwood of Bulnesia sarmientoi, a tree native from Latin America. Despite being widely used in perfumery, guaiacwood oil has been poorly described in the past. This study aims at giving an in-depth characterisation of its chemical composition as well as disclosing the odorant compounds responsible for its characteristic fragrance. Our methodology was based on a combination of fractionation and analytical techniques, including comprehensive two-dimensional gas chromatography coupled to mass spectrometry and preparative capillary-gas chromatography. The entire analytical work led to the isolation of 20 constituents among which 14 have never been reported so far in natural extracts. Each isolated compound was fully characterised by spectroscopic methods. Finally, the accurate knowledge of the chemical composition permitted the identification of the odour-active constituents by gas chromatography-olfactometry.

Revisiting the Chemistry of Guaiacwood Oil: Identification and Formation Pathways of 5,11- and 10,11-Epoxyguaianes

Guaiacwood oil from Bulnesia sarmientoi Lorentz ex. Griseb is a common natural ingredient of the perfume industry used in both domestic and luxury fragrances for its highly appreciated woody-rosy odor, as well as its excellent fixative properties. Despite its long and traditional use as a perfume ingredient, guaiacwood oil has not been extensively studied. Thus, the chemical characterization of its constituents by using a full array of GC-hyphenated techniques (GC-MS, GC × GC-MS, and pc-GC) combined with conventional chemical fractionation was undertaken. In the course of this work, 15 new sesquiterpenoids mostly belonging to the 5,11- and 10,11-epoxyguaiane families were identified. Each isolated compound was fully characterized by NMR and MS. Collectively, the specific chemical relationships observed between sesquiterpene oxides and alcohols permitted the formulation of probable formation pathways regarding their presence as natural constituents of guaiacwood extracts.

Integrated comprehensive two-dimensional gas-chromatographic and spectroscopic characterization of vetiveryl acetates: Molecular identifications, quantification of constituents, regulatory and olfactory considerations

Vetiveryl acetate is a common ingredient of the perfume industry highly prized by perfumers for its crisp vetiver note and thus often used in high-end perfume compositions. Vetiveryl acetate is currently manufactured from vetiver oil by means of various industrial processes that result in the conversion of the main vetiver alcohols into their corresponding acetates. Despite being used for decades as perfume ingredient, vetiveryl acetate has barely been studied in the past, therefore its chemical composition is poorly documented. While vetiveryl acetate is currently under investigation by regulation authorities, it was crucial to fill this gap of knowledge. We report here the first detailed investigation of different types of vetiveryl acetates, covering analytical, regulatory, and olfactory aspects. This study is based upon an integrated analytical methodology involving a full array of gas chromatographic techniques and spectroscopic/spectrometric methods. The principal objective was the identification of the main ester constituents contained in different samples of vetiveryl acetate, as well as linking their chemical composition with their manufacture process. Among the major esters detected in all samples, 23 ester constituents were either isolated by capillary preparative-gas chromatography or synthesized in order to provide their complete spectral characterization. The quantification of constituents in both commercial and laboratory-made vetiveryl acetates was carried out by internal calibration using comprehensive two-dimensional-gas chromatography and predicted relative response factors. The generated set of analytical data permitted to explore both the regulatory aspects and the olfactory properties associated with the substance. The manufacture of vetiveryl acetate modulates the initial scent of vetiver essential oil by suppressing the notes brought by the main fragrant alcohols. While the impact of undesired odorant molecules such as phenol derivatives and geosmin is lowered, the major odour-active ketones such as khusimone, ziza-6(13)-en-3-ones, and the two vetivones develop their own odor characters in vetiveryl acetate.