Gas chromatographic techniques and spectroscopic approaches for a deep characterization of Piper gaudichaudianum Kunth essential oil from Brazil.

Piper gaudichaudianum Kunth essential oil (EO) is a natural source of bioactive components, having multiple therapeutic applications. Its chemical composition is highly variable, and strictly depends on abiotic factors, resulting in various biological activities. The present study details the utilization of multiple gas chromatographic techniques alongside nuclear magnetic resonance (NMR) spectroscopy to characterize the essential oil of Piper gaudichaudianum Kunth from Brazil. Seventy-six components were identified using GC-MS analysis, while enantio­selective multidimensional gas chromatography elucidated the enantiomeric distribution of eight chiral components, for the first time in the literature. Following GC-MS analysis, an unidentified component, constituting approximately 27 % of the total oil, prompted an isolation step through preparative gas chromatography. Through the combined use of nuclear magnetic resonance, GC-Fourier transform infrared spectroscopy (FTIR), and mass spectrometry (MS), the unknown molecule was structurally identified as 4-[(3E)­dec-3-en-1-yl]phenol. Remarkably, it was identified as a known molecule, gibbilimbol B, and not previously listed in any MS database. Subsequently, the spectrum was included in a commercial library, specifically the FFNSC 4.0 MS database, for the first time.

Parallel coupling of gas chromatography to mass spectrometry and solid deposition Fourier transform infrared spectroscopy: an innovative approach to address challenging identifications.

The request for novel hyphenated instruments and techniques, capable of affording exhaustive information and results, is a focus continuously watched out. In this context, the present work aimed at the development of an integrated system combining gas chromatographic (GC) separation with mass spectrometry (MS) and (solid deposition) Fourier transform infrared spectroscopy (FTIR) detection. An external transfer line was designed in the lab for the parallel coupling of the two detectors, in such a way to obtain complementary analytical information consisting of an MS spectrum, an IR spectrum and linear retention indices (LRI), within a single analysis. The instrument performance was demonstrated for the analysis of a commercial mixture consisting of 139 hydrocarbons, comprising linear, branched, unsaturated and aromatic compounds. A 100-m poly(dimethylsiloxane) column was employed for the separation, and the outlet flow was split 95:5 between the IR and MS detectors using two uncoated capillaries. The IR spectra were acquired from solid deposits on a zinc selenide disc (-90 °C), over a spot (detector area) of about 0.1 mm2, in the range of 4000-700 cm-1 and at a resolution of 4 cm-1. Final identification of the separated compounds by a library search was achieved by excluding incorrect results, sequentially using a three-filter approach (85% similarity against reference MS and IR library spectra and ±10 LRI unit tolerance). Based on these preliminary results, the GC-MS/sd-FTIR system is a promising tool for the characterization of complex matrix constituents, for which identification is cumbersome, by using only one detection technique.

From grape to wine: A thorough compound specific isotopic, enantiomeric and quali-quantitative investigation by means of gas chromatographic analysis.

In this study, multiple analytical approaches, including simultaneous enantiomeric and isotopic analysis, were employed to thoroughly investigate the volatile fraction in Moscato giallo grape berries and wines. For the qualitative and quantitative profiling, a fast GC-QqQ/MS approach was successfully utilized. However, prior to isotopic analysis, the extracts underwent an additional concentration step, necessitating an assessment of isotopic fractionation during the concentration process. Once the absence of carbon isotopic fractionation was confirmed, this research aimed to develop a suitable gas chromatographic method for the simultaneous detection of both enantiomeric and isotopic ratios of target monoterpenoids in Moscato giallo samples. To address the limitations associated with a one-dimensional approach, multidimensional gas chromatography was employed to enhance separation before IRMS and qMS detections. Utilizing a Deans switch transfer device, the coupling of an apolar column in the first dimension and a chiral cyclodextrin-based stationary phase in the second dimension proved effective for this purpose. The data obtained from the analysis of Moscato giallo samples allowed for the assessment of natural isotopic and enantiomeric distributions in grapes and wines for the first time in the literature. Significant enantiomeric excesses were observed for the target terpenoids investigated. Regarding isotopic distribution, a consistent trend was observed for all detected target terpenols, including the linalool enantiomers. To date, this study represents the first investigation of simultaneous δ13C and chiral investigation of the main terpenoids in oenological products in the literature.

Profiling of seized Cannabis sativa L. flowering tops by means of microwave-assisted hydro distillation and gas chromatography analyses.

This research aimed to support police forces in their battle against illicit drug trafficking by means of a multi-technique approach, based on gas chromatography. In detail, this study was focused on the profiling of volatile substances in narcotic Cannabis sativa L. flowering tops. For this purpose, the Scientific Investigation Department, RIS Carabinieri of Messina, provided 25 seized samples of Cannabis sativa L. The content of Δ9-tetrahydrocannabinol (THC), useful to classify cannabis plant as hemp (≤ 0.2 %) or as marijuana (> 0.2 %), was investigated. Essential oils of illicit drug samples were extracted using a microwave-assisted hydro-distillation (MAHD) system; GC-MS and GC-FID analytical techniques were used for the characterization of the terpenes and terpenoids fingerprint. Furthermore, the enantiomeric and carbon isotopic ratios of selected chiral compounds were investigated using a heart-cutting multidimensional GC (MDGC) approach. The latter exploited a combination of an apolar column in the first dimension, and a chiral cyclodextrin-based column in the second one, prior to parallel isotope-ratio mass spectrometry (C-IRMS) and MS detection. Finally, all the data were gathered into a statistical model, to demonstrate the existence of useful parameters to be used for the classification of seized samples.

Chiral isotopic fractionation in lemon essential oil: A tool for authenticity assessment?

The present research aimed to retrieve key information about the genuineness of Sicilian lemon essential oils by evaluating simultaneously the chiral and isotopic data of target terpene components. With respect to previous literature references, where chiral recognition and isotope discrimination were performed by distinct gas chromatographic methods, this study aimed to develop a single analytical approach. To overcome limitations associated to monodimensional gas chromatographic approaches, an enantio­selective multidimensional gas chromatographic approach coupled to isotopic ratio mass spectrometry and to parallel single quadrupole detection (Es-MDGC-C-IRMS/qMS) was developed. Thanks to the features of this system, enantiomeric excesses and target δ13C of the chiral and achiral components were evaluated in a single gas chromatographic run, allowing to reduce total time analysis, as well the consumption of electricity, solvents and samples. Moreover, due to the capability to baseline separate the enantiomeric couples, further considerations were done about the specific δ13C value of the target separated enantiomers. Dealing with the genuine lemon oils analysed, a different δ13C value was found between the enantiomers of the same chiral component, namely (-) and (+) of α and ß-pinene, suggesting a different isotopic fractionation related to a specific biosynthetic pathway. This research aimed to evaluate the reasons behind this behaviour, paving the way to newer considerations in the field of authenticity assessment.

Simultaneous evaluation of the enantiomeric and carbon isotopic ratios of Cannabis sativa L. essential oils by multidimensional gas chromatography.

Recent times have witnessed an upsurge of interest in hemp and hemp-derived products, as driven by the scientific findings specific to the pharmacological properties of Cannabis sativa L. and its constituents. There has been evidence that the terpene profile, along with the cannabinoid content, produces in humans the effects associated with different strains, beyond fragrance perception. A great deal of effort has been put into developing analytical approaches to strengthen the scientific knowledge on cannabis essential oil composition and provide effective tools for ascertaining the authenticity of commercial cannabis samples. For this concern, enantio-selective-GC-C-IRMS has proven to be effective for assessing the ranges characteristic of the genuine samples and detecting any fraudulent additions. This research aimed at providing for the first time the enantiomeric and isotopic ratios of target terpenes in cannabis essential oils, obtained from microwave-assisted hydro-distillation from the fresh and dried inflorescences of different cannabis varieties. Implementing multidimensional gas chromatography separation was mandatory prior to detection, in order to obtain accurate δ13C values and enantiomeric data from completely separated peaks. For this purpose, a heart-cut method was developed, based on the coupling of an apolar first dimension column to a secondary chiral cyclodextrin-based stationary phase. Afterwards, the data gathered from enantio-selective-MDGC-C-IRMS/qMS analysis of a set of genuine samples were used to evaluate the quality of nineteen commercial cannabis essential oils purchased from local stores. Remarkably, the data in some cases evidenced enantiomeric ratios and δ13C values outside the typical ranges of genuine oils. Such findings suggest the usefulness of the method developed to ascertain the genuineness and quality of cannabis essential oils.

Overcoming the lack of reliability associated to monodimensional gas chromatography coupled to isotopic ratio mass spectrometry data by heart-cut two-dimensional gas chromatography.

The use of IRMS as a GC detector has a history going back decades, however the critical issue of wrong δ13C measurements resulting from impure peaks has been often underestimated. To this regard, multidimensional separation techniques are effective tools to improve the reliability of the data, with respect to those obtained after monodimensional analysis. The present research aims to draw attention to one critical issue, related to the reliability of the δ13C data obtained by means of monodimensional GC-C-IRMS. Although already known from the literature, such aspect has been greatly overlooked, as is reflected in the few papers reporting the use of MDGC, among the plethora of published research dealing with GC-C-IRMS applications. Hereby, a set of natural samples of complex composition were analysed to investigate the presence of minor or even undetected coelutions, and to which extent it affected the isotope ratio determination. Apart from chromatographic effects, and issues related to analytes conversion to CO2 prior to IRMS measurement, unpredictable co-elutions with compounds, either resulting from oxidation or intentionally added in fraudulent practices, could also contribute to a shift of the δ13C data, up to 10‰ and higher. Last, the influence of column bleed was investigated, as affecting the determination of the δ13C data for compounds that were eluted at high temperatures. It was finally demonstrated by the selected key studies that implementation of MDGC separation is mandatory to prevent the aforementioned issues, aiming to guarantee accurate results. In the light of the above conclusions, and considering the level of automation of heart-cut devices nowadays available, routine practice of MDGC results highly recommendable in any IRMS applications.

Collection and identification of an unknown component from Eugenia uniflora essential oil exploiting a multidimensional preparative three-GC system employing apolar, mid-polar and ionic liquid stationary phases.

The present research deals with the collection and structural elucidation of an unknown component, accounting for about 35% of the essential oil obtained upon distillation of the leaves of Eugenia uniflora L., harvested during summer (January, 2017) in Paraná State (Southern Brazil). A multidimensional gas chromatographic preparative system, based on the coupling of three GC systems equipped with apolar, PEG and ionic liquid-based stationary phases, was successfully applied for the isolation of the chromatographic band relative to the unknown molecule. The use of wide-bore columns allowed for an increased sample capacity compared to conventional micro-bore columns, thus the injection of a neat sample was feasible, greatly reducing the total collection time. A higher chromatographic efficiency was afforded by the use of a multidimensional approach in the heart-cut mode, exploiting the different selectivity of three stationary phases, which ensured the attainment of a highly pure fraction. In only five runs, more than 3 milligrams were collected, with an average purity greater then 95%. Finally, the unknown component was subjected to nuclear magnetic resonance spectroscopy, mass spectrometry and condensed phase Fourier-transform infrared spectroscopy, leading to the identification of 6-ethenyl-6-methyl-3,5-di(prop-1-en-2-yl)cyclohex-2-en-1-one. The presented approach has been demonstrated to be effective for the isolation and structural elucidation of unknown molecules in complex samples, which will allow for further in-depth studies, like biological evaluation or pharmacological tests.

Multidimensional Gas Chromatography Coupled to Combustion-Isotope Ratio Mass Spectrometry/Quadrupole MS with a Low-Bleed Ionic Liquid Secondary Column for the Authentication of Truffles and Products Containing Truffle.

Truffles are among the most expensive foods available in the market, usually used as flavoring additives for their distinctive aroma. The most valuable species is Tuber magnatum Pico, better known as "Alba white truffle", in which bis(methylthio)methane is the key aroma compound. Given the high economical value of genuine white truffles, analytical approaches are required to be able to discriminate between natural or synthetic truffle aroma. Gas chromatography coupled to combustion-isotope ratio mass spectrometry (GC-C-IRMS), exploiting the 13C/12C ratio abundance of the key flavorings compounds in foods, has been a recognized technique for authenticity and traceability purposes; however, a number of issues have greatly limited its widespread use so far. In the present research, a high-efficiency HS-SPME MDGC-C-IRMS with simultaneous quadrupole MS detection has been applied for the evaluation of bis(methylthio)methane, resolving the coelution occurring with other components. With the aim to minimize the effect of column bleeding on δ13C measurement, a medium polarity ionic liquid-based stationary phase was preferred to a polyethylene glycol one, as the secondary column. In total, 24 genuine white truffles harvested in Italy were analyzed, attaining a δ13C values between -42.6‰ and -33.9‰, with a maximum standard deviation lower than 0.7‰. Two commercial intact truffles and 14 commercial samples of pasta, sauce, olive oil, cream, honey, and fresh cheese flavored with truffle aroma were analyzed, and the results from δ13C measurement were evaluated in comparison with those of genuine "white truffle" range and commercial synthetic bis(methylthio)methane standard.

Quali-quantitative characterization of the volatile constituents in Cordia verbenacea D.C. essential oil exploiting advanced chromatographic approaches and nuclear magnetic resonance analysis.

Cordia verbenacea D.C. (Boraginaceae, Varronia curassavica Jacq. synonym) is a medicinal plant, native from Brazil, especially the leaves are used in folk medicine. The aim of this study was to extend the characterization of the volatile fraction of the essential oil obtained from this plant, by using GC-FID, GC-MS, and chiral GC. Moreover, to further clarify the composition of the volatile fraction, preparative multidimensional-GC (prep-MDGC) was used to collect unknown compounds, followed by NMR characterization. Specifically, the chemical characterization, both qualitative and quantitative, of the volatile fraction of the essential oil obtained from Cordia verbenacea cultivated in the Minas Gerais area (central area of Brazil) was investigated for the first time. The principal components from a quantitative point of view were α-pinene (25.32%; 24.48g/100g) and α-santalene (17.90%; 17.30g/100g), belonging to the terpenes family. Chiral-GC data are reported for the enantiomeric distribution of 7 different components. Last, to obtain the complete characterization of the essential oil constituents, prep-MDGC analysis was used to attain the isolation of two compounds, not present in the principal MS databases, which were unambiguously identified by NMR investigation as (E)-α-santalal and (E)-α-bergamotenal, reported for the first time in Cordia verbenacea essential oil.

Rapid isolation, reliable characterization, and water solubility improvement of polymethoxyflavones from cold-pressed mandarin essential oil.

Polymethoxyflavones possess many biological properties, as lipid-lowering, hypoglycaemic, anti-inflammatory, antioxidant, and anticancer activities, therefore, they may be employed as nutraceuticals or therapeutic agents. The scarcity of pure polymethoxyflavones on the market as well as their low water solubility limited in vivo studies and the use of polymethoxyflavones as food or pharmaceutical supplements. Since mandarin peels are a rich source of polymethoxyflavones, tangeretin, nobiletin, sinensetin, tetra-O-methyl scutellarein, and heptamethoxyflavone were purified from a nonvolatile residue of a cold-pressed mandarin essential oil using a multidimensional preparative liquid chromatographic system coupled with a photodiode array detector and a single quadrupole mass spectrometer. A new prototype, consisting of a nano-liquid chromatography system coupled with an electron ionization mass spectrometer, was used for the characterization of the pure isolated molecules. Finally, due to the collection of highly pure nobiletin and tangeretin, the ability of 2-hydroxypropyl-ß-cyclodextrin to enhance the water solubility of both polymethoxyflavones was evaluated by phase solubility studies and Job's plot method.

Enhanced resolution of Mentha piperita volatile fraction using a novel medium-polarity ionic liquid gas chromatography stationary phase.

The evaluation of a novel medium-polarity ionic-liquid-based gas chromatography column, SLB-IL60, towards the analysis of a complex essential oil, namely, a peppermint essential oil sample, is reported. The SLB-IL60 30 m column was subjected to bleeding measurements, by means of conventional gas chromatography with mass spectrometry. The SLB-IL60 column was then evaluated in the analysis of pure standard compounds, chosen as typical constituents of peppermint essential oil. Resolution and peak symmetry (expressed as tailing factors at 10% of peak height) were measured and the results were compared to those obtained on the most widely used columns in such an application, namely a medium-polarity [100% poly(ethyleneglycol)] stationary phase, and an apolar 5% diphenyl/95% dimethyl siloxane. The final part of the evaluation was dedicated to the gas chromatography with mass spectrometry analysis of a peppermint essential oil sample and again the data were compared to those obtained on the 100% poly(ethyleneglycol) and the 5% diphenyl/95% dimethyl siloxane phase. Linear retention indices were determined for all the identified components on the ionic liquid capillary.

Improvement of mineral oil saturated and aromatic hydrocarbons determination in edible oil by liquid-liquid-gas chromatography with dual detection.

Mineral oils, which are mainly composed of saturated hydrocarbons and aromatic hydrocarbons, are widespread food contaminants. Liquid chromatography coupled to gas chromatography with flame ionization detection represents the method of choice to determine these two families. However, despite the high selectivity of this technique, the presence of olefins (particularly squalene and its isomers) in some samples as in olive oils, does not allow the correct quantification of the mineral oil aromatic hydrocarbons fraction, requiring additional off-line tools to eliminate them. In the present research, a novel on-line liquid chromatography coupled to gas chromatography method is described for the determination of hydrocarbon contamination in edible oils. Two different liquid chromatography columns, namely a silica one (to retain the bulk of the matrix) and a silver-ion one (which better retains the olefins), were coupled in series to obtain the mineral oil aromatic hydrocarbons hump free of interfering peaks. Furthermore, the use of a simultaneous dual detection, flame ionization detector and triple quadrupole mass spectrometer allowed us not only to quantify the mineral oil contamination, but also to evaluate the presence of specific markers (i.e. hopanes) to confirm the petrogenic origin of the contamination.

Determination of phthalate esters in vegetable oils using direct immersion solid-phase microextraction and fast gas chromatography coupled with triple quadrupole mass spectrometry.

Phthalates are a group of synthetic compounds mainly used as plasticizers, which have been classified as endocrine-disrupting chemicals and potential human-cancer causing agents. They can be found in high amounts in foods, deriving mainly from plastic packaging. The analytical determination of these compounds is very challenging since they are ubiquitous. Therefore, minimization of sample manipulation is highly desirable. The present work exploited the application of a solid-phase microextraction method for the analysis of phthalates in vegetable oil. A preliminary comparison between a polydimethylsiloxane (PDMS) and a Carbopack Z/PDMS fiber was carried out both in the headspace and direct immersion extraction modes. Before immersing the fiber, a rapid liquid-liquid extraction was performed using acetonitrile to remove the bulk of triglycerides. PDMS in the direct immersion mode showed the best performance. The method was fully validated obtaining a good linearity with a coefficient of correlation of over 0.9960 for all compounds, repeatability and accuracy values generally better than 10%, and very good limit of quantification values.

Performance evaluation of a versatile multidimensional chromatographic preparative system based on three-dimensional gas chromatography and liquid chromatography-two-dimensional gas chromatography for the collection of volatile constituents.

The present research deals with the multi-collection of the most important sesquiterpene alcohols belonging to sandalwood essential oil, as reported by the international regulations: (Z)-α-santalol, (Z)-α-trans bergamotol, (Z)-ß-santalol, epi-(Z)-ß-santalol, α-bisabolol, (Z)-lanceol, and (Z)-nuciferol. A versatile multidimensional preparative system, based on the hyphenation of liquid and gas chromatography techniques, was operated in the LC-GC-GC-prep or GC-GC-GC-prep configuration, depending on the concentration to be collected from the sample, without any hardware or software modification. The system was equipped with a silica LC column in combination with polyethylene glycol-poly(5% diphenyl/95% dimethylsiloxane)-medium polarity ionic liquid or ß-cyclodextrin based GC stationary phases. The GC-GC-GC-prep configuration was exploited for the collection of four components, by using a conventional split/splitless injector, while the LC-GC-GC-prep approach was applied for three low abundant components (<5%), in order to increase the quantity collected within a single run, by the LC injection of a high sample amount. All target compounds, whose determination is hampered by the unavailability of commercial standards, were collected at milligram levels and with a high degree of purity (>87%).

Evaluation of a novel helium ionization detector within the context of (low-)flow modulation comprehensive two-dimensional gas chromatography.

The present research is focused on the use and evaluation of a novel helium ionization detector, defined as barrier discharge ionization detector (BID), within the context of (low-)flow modulation comprehensive two-dimensional gas chromatography (FM GC×GC). The performance of the BID device was compared to that of a flame ionization detector (FID), under similar FM GC×GC conditions. Following development and optimization of the FM GC×GC method, the BID was subjected to fine tuning in relation to acquisition frequency and discharge flow. Moreover, the BID performance was measured and compared to that of the FID, in terms of extra-column band broadening, sensitivity and dynamic range. The comparative study was carried out by using standard compounds belonging to different chemical classes, along with a sample of diesel fuel. Advantages and disadvantages of the BID system, also within the context of FM GC×GC, are critically discussed. In general, the BID system was characterized by a more limited dynamic range and increased sensitivity, compared to the FID. Additionally, BID and FID contribution to band broadening was found to be similar under the operational conditions applied. Particular attention was devoted to the behaviour of the FM GC×GC-BID system toward saturated and aromatic hydrocarbons, for a possible future use in the field of mineral-oil food contamination research.

Rapid isolation of high solute amounts using an online four-dimensional preparative system: normal phase-liquid chromatography coupled to methyl siloxane-ionic liquid-wax phase gas chromatography.

This study reports the recent evolution of a multidimensional GC-GC-GC preparative system, now combined with an online LC preseparation step, operated under normal phase conditions. It is herein shown that the four-dimensional instrument can collect sample components with a concentration lower than 10%, in a short time period, while maintaining a high level of analyte purity. The LC dimension allows (I) the injection of higher sample amounts, compared to "direct" GC injection; (II) a polarity-based preseparation, leading to the GC injection of simplified subsamples, and thus reducing the possibility of coelutions; (III) to eliminate the essential-oil "matrix", replacing it with the LC mobile phase (the GC system is more protected from potential contamination); (IV) the LC mobile phase is of much lower viscosity with respect to a pure, or highly concentrated essential oil, avoiding difficulties in the syringe sample withdrawal process, prior to GC injection. System optimization was performed by using standard solutions; in addition, a very complex sample, namely, vetiver essential oil, was subjected to the preparative process, with the scope of isolating two low-amount constituents (namely, α-amorphene and ß-vetivone). The latter two sesquiterpenoids, which accounted for 1.7 and 4.0% of the sample (considering the volatiles), respectively, were successfully collected at the milligram level, in a one-day work period, with a purity degree in excess of 90%.

Rapid collection and identification of a novel component from Clausena lansium Skeels leaves by means of three-dimensional preparative gas chromatography and nuclear magnetic resonance/infrared/mass spectrometric analysis.

The present research reports the use of a three-dimensional preparative gas chromatography (prep GC) system, equipped with three Deans-switch devices and 5%diphenyl/wax/mid-polarity ionic liquid stationary phases, for the isolation of volatile components from a complex natural source, namely wampee essential oil (derived from Clausena lansium Skeels leaves). Collection was performed by using a simple and effective lab-constructed trapping device. Initially, an unknown (and abundant) wampee oil constituent was erroneously identified as α-sinensal, through an MS database search (a low similarity match was attained), performed after a GC-quadMS experiment., The unknown compound was then the isolated by using the novel prep GC system, in a highly pure form (at the mg level), and was correctly identified by using nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR) and mass spectrometry (MS). Both FTIR and MS data were used to confirm the NMR information. The name given to the molecule was (2E,6E)-2-methyl-6-(4-methylcyclohex-3-enylidene)hept-2-enal. The results herein described will demonstrate the need for a high-resolution GC step, prior to analyte collection, in the prep GC analysis of complex samples.

Determination of petitgrain oils landmark parameters by using gas chromatography-combustion-isotope ratio mass spectrometry and enantioselective multidimensional gas chromatography.

Gas chromatography-combustion-isotope mass spectrometry was employed for the assessment of the Carbon isotope ratios of volatiles in Italian mandarin and lemon petitgrain oils. In addition, the composition of the whole oil and the enantiomeric distribution of selected chiral compounds were determined for all the samples by using gas chromatography and by multidimensional and conventional enantioselective gas chromatography. The composition of the oils was compared with previous studies. The enantiomeric distribution of lemon petitgrain oils is here reported for the first time. On the composition of mandarin petitgrain oil, the information available in literature, to date, is relative only to one sample from Egypt. Carbon isotope ratio of several terpene hydrocarbons and of their oxygenated derivatives contained in petitgrains was compared with the δ (13)C(VPDB) values of the same compounds present in the corresponding genuine Italian Citrus peel oil. The results prove that the isotopic values obtained for lemon and mandarin petitgrain oils are very close to those relative to the corresponding peel oils determined in previous studies.