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Quality control of essential oils is fundamental for verifying their authenticity and conformity with quality standards, ensuring their safety and regulatory compliance, and monitoring their consistency. Companies that produce or market essential oils routinely evaluate the quality and authenticity of their products. However, they also must deal with increasing attention to environmental sustainability as well as practical considerations such as productivity, cost, and simplicity of methods. In this study, enantioselective gas chromatography (GC) was adopted to evaluate the quality of sweet and bitter orange essential oils, used as a case study. The analytical conditions were optimized and translated to fast GC to evaluate the impact of this approach on the environmental footprint of the analyses. The greenness of fast GC, compared with conventional GC, was quantitatively evaluated using a dedicated metric tool (AGREE), and important improvements have been calculated. The developed methods were applied to a set of commercial essential oils, and the data about the enantiomeric composition and relative percentage abundance were elaborated through multivariate statistics (principal component analysis). The results showed that fast chiral gas chromatography enables the classification of citrus essential oil samples and can be considered an environmentally friendly and sustainable approach for evaluating their quality. [ABSTRACT FROM AUTHOR]

The fragrance industry plays a key role in the global economy, producing a wide range of personal care and household products. However, some fragrance ingredients have been linked to allergic reactions in sensitive people, and their concentrations are regulated at the European level. For this reason, reliable, rapid, and sustainable analytical methods are needed to rapidly detect and quantify these compounds. Recently, a new class of hydrophobic eutectic solvents (HES) has been introduced; they consist of natural terpenoids or phenolic compounds that can be used as hydrogen bond donors (HBD) and acceptors (HBA), and they are more suitable for GC applications due to their higher volatility. In this study, a dispersive liquid–liquid microextraction (DLLME) approach is proposed for the analysis and quantification of a range of allergens in hydroalcoholic perfumes. The optimized method requires only 50 µL of a natural HES (thymol–eugenol), which is readily dispersed by vortexing in 2 mL of sample. After centrifugation, the HES rich phase is diluted in 400 µL EtOH and directly injected into the GC-FID system. The proposed method has been successfully applied in the analysis and quantification of commercial fragrances, demonstrating good enrichment of target allergens and suitability for aqueous matrices analysis. [ABSTRACT FROM AUTHOR]

This review is an overview of the recent advances of gas chromatography in essential oil analysis; in particular, it focuses on both the new stationary phases and the advanced analytical methods and instrumentations. A paragraph is dedicated to ionic liquids as gas chromatography stationary phases, showing that, thanks to their peculiar selectivity, they can offer a complementary contribution to conventional stationary phases for the analysis of complex essential oils and the separation of critical pairs of components. Strategies to speed‐up the analysis time, thus answering to the ever increasing request for routine essential oils quality control, are also discussed. Last but not least, a paragraph is dedicated to recent developments in column miniaturization in particular that based on microelectromechanical‐system technology in a perspective of developing micro‐gas chromatographic systems to optimize the energy consumption as well as the instrumentation dimensions. A number of applications in the essential oil field is also included. [ABSTRACT FROM AUTHOR]

The frankincense resins, secreted from Boswellia species, are an uncommon example of a natural raw material where every class of terpenoids is present in similar proportions. Diterpenoids (serratol, incensole, and incensole acetate) are used to discriminate samples from different species and origins. Headspace solid‐phase microextraction has been used for frankincense analysis, although it requires long sampling time for medium‐ to low‐volatility markers; headspace solid‐phase microextraction under vacuum can overcome this limit. Gas chromatography is used for analysis but the separation of incensole and serratol needs polar stationary phases. In this study, we develop a method to discriminate frankincenses based on vacuum‐assisted headspace solid‐phase microextraction combined with fast gas chromatography‐mass spectrometry with ionic liquid–based stationary phases. The optimized conditions for solid samples were: air evacuation below 0°C, 15 min of incubation time, and 15 min of extraction time. Losses of volatiles due to vial air‐evacuation in the presence of the sample were minimized by sample amount above 100 mg and low sample temperature. Fast gas chromatography provides the baseline separation of all markers in 20 min. By applying vacuum sampling and fast gas chromatography, the total analysis was reduced to 50 min compared to 120 min (60 min sampling plus 60 min analysis) as previously reported. The method was successfully applied to commercial frankincense samples. [ABSTRACT FROM AUTHOR]

The volatile fraction of natural products often consists of complex mixtures of isomeric and/or homologous components with similar structural and physical characteristics (e.g. mono- and sesquiterpenoids) that are not easy to separate simultaneously with conventional GC stationary phases, even when used with multidimensional systems. The introduction of ionic liquids (ILs) as stationary phases has opened up new perspectives in this field as their unique solvation properties result in uncommon selectivity, which is completely different to that of classic polydimethylsiloxane (PDMS)- and polyethyleneglycol (PEG)-based columns. Because of their peculiar selectivity and high inertness, IL-based columns have already found several applications in the natural product field in mono- and multidimensional GC and preparative GC, leading to the exhaustive analysis of complex samples (including aqueous solutions), and the separation of challenging pair(s) of compounds. This article provides an overview of how IL-based columns can be exploited in the fields of food and natural products, explores the wide range of applications that have already been developed and highlights the main features of these promising stationary phases, which are expected to be further extended in the near future, in particular, for routine use. [ABSTRACT FROM AUTHOR]

Fragrances and products deriving from essential oils are often formulated or diluted in aqueous media, usually ethanol/water. Gas chromatography (GC) is the technique of choice to analyze volatiles. However, when using columns coated with conventional stationary phases, its application to aqueous samples often requires time-consuming and/or discriminative sample preparation techniques to extract the target analytes from the aqueous medium, so as to avoid its direct injection. In GC with conventional columns, water produces peak asymmetry, poor sensitivity and efficiency, strong adsorption, stationary phase degradation, and, last but not least, it is not easy to detect reliably when present in high amounts. In 2012, Armstrong’s group introduced new fully water-compatible ionic-liquid (IL)-based GC capillary columns based on phosphonium and imidazolium derivative cations combined with trifluoromethanesulphonate. These columns were recently made available commercially by Supelco, under the trade name Watercol™. These derivatives maintain IL’s unique selectivity and chromatographic properties, and enable water to be used as injection solvent, thus avoiding the sample preparation procedures required by conventional columns. This study reports and critically discusses the results of commercially available water-compatible IL columns for direct analysis of aqueous samples in the fragrance and essential oil fields by GC with thermal conductivity (TCD) and/or flame ionization detectors (FID). The results showed that water-compatible IL-based stationary phases can successfully be adopted for qualitative and quantitative analysis of fragrances and essential oils directly diluted in aqueous solvents. On the other hand, the study also shows that their inertness needs to be further increased and (possibly) the range of operative temperature extended when water is the main solvent of the sample. [ABSTRACT FROM AUTHOR]

A simple and rapid ionic liquid (IL)-based in situ dispersive liquid-liquid microextraction (DLLME) method was developed and coupled to headspace gas chromatography (HS-GC) employing electron capture (ECD) and mass spectrometry (MS) detection for the analysis of polychlorinated biphenyls (PCBs) and acrylamide at trace levels from milk and coffee samples. The chemical structures of the halide-based ILs were tailored by introducing various functional groups to the cations to evaluate the effect of different structural features on the extraction efficiency of the target analytes. Extraction parameters including the molar ratio of IL to metathesis reagent and IL mass were optimized. The effects of HS oven temperature and the HS sample vial volume on the analyte response were also evaluated. The optimized in situ DLLME method exhibited good analytical precision, good linearity, and provided detection limits down to the low ppt level for PCBs and the low ppb level for acrylamide in aqueous samples. The matrix-compatibility of the developed method was also established by quantifying acrylamide in brewed coffee samples. This method is much simpler and faster compared to previously reported GC–MS methods using solid-phase microextraction (SPME) for the extraction/preconcentration of PCBs and acrylamide from complex food samples. [ABSTRACT FROM AUTHOR]

This article deals with enantioselective gas chromatography (Es-GC) utilizing cyclodextrin derivatives as chiral stationary phases (CSPs) for chiral recognition in the flavour and fragrance field. It consists of two main parts. The first one concerns cyclodextrins and their use in Es-GC, and it deals with their introduction and evolution as CSPs in GC, together with some theoretical aspects involved with enantiomeric separation and their consequent influence on routine chiral recognition. The second part reports on the strategy of chiral recognition in routine analysis with cyclodextrin derivatives as CSP, illustrated with examples from the authors' everyday experiences. This part describes how to identify enantiomers or to measure their excess or ratio determination in complex mixtures; in particular, it discusses the opportunities offered by multidimensional and fast GC techniques, the role of mass spectrometry, and the application of total analysis systems to chiral recognition. [ABSTRACT FROM AUTHOR]

Highlights: [•] High concentration capacity sample preparation for GC×GC–MS food profiling. [•] High-throughput profiling and fingerprinting for sensomics. [•] Sorption based sample preparation for successful definition of milk aroma blueprint. [•] Fully-integrated system of multiple dimension analysis for sensomics. [ABSTRACT FROM AUTHOR]

The 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. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Abstract: Ionic liquids (ILs) are of great interest as moderately polar to polar stationary phases for GC, because their selectivity differs markedly from that of conventionally used phases. In the flavor, fragrance and essential oil fields, analysts often deal with complex mixtures of compounds having similar structural and physical characteristics (e.g., mono- and sesquiterpenoids), therefore requiring an interactive combination between chromatographic and mass spectral data for correct identification. New GC stationary phases with different selectivity must therefore be continually tested. Performance and evolution over time of commercially available IL columns versus those commonly used in these fields are here evaluated, mainly in view of their routine use. Chromatographic and separative properties (efficiency, separation capability, inertness and/or activity) of commercially available IL columns were compared to those of columns coated with 5% phenyl–95% methylpolysiloxane, 14% cyanopropyl–86% polysiloxane, and polyethylene glycol, on different complexity samples, including standard mixtures of volatile suspected allergens and pesticides, and cornmint and vetiver essential oils. The results show that IL columns can successfully be used for a wide range of applications characteristic of these fields, mainly because of their unusual selectivity, in particular when separations based on functional groups are required. Moreover, the latest generation of IL columns (IL61 and IL60) presents chromatographic performance comparable to or only slightly lower than that of the conventional columns routinely used in these fields. [Copyright &y& Elsevier]

Abstract: Asymmetrically substituted 6I-VII-O-t-butyldimethylsilyl(TBDMS)-3I-VII-O-ethyl-2I-VII-O-methyl-β-cyclodextrin (MeEt-CD) and 6I-VII-O-TBDMS-2I-VII-O-ethyl-3I-VII-O-methyl-β-cyclodextrin (EtMe-CD) were synthesised to evaluate the role of the substitution pattern in positions 2 and 3 on the enantioselectivity, in particular in view of their application to routine analysis in fast enantioselective gas chromatography (Es-GC). The chromatographic properties and enantioselectivities of the new derivatives were tested by separating the enantiomers of a series of medium-to-high volatility racemates in the flavour and fragrance field, and compared to those of the corresponding symmetrically substituted 6I-VII-O-TBDMS-2I-VII,3I-VII-O-methyl-β-CD (MeMe-CD) and 6I-VII-O-TBDMS-2I-VII,3I-VII-O-ethyl-β-CD (EtEt-CD), and were then applied to analysis of real-world essential oil (e.o.) samples. A new synthetic process including the sonochemical approach to obtain synthetic reproducibility and significant yields of the per-substituted derivatives with acceptable reaction times was developed. The results show that asymmetrically substituted methyl/ethyl CDs compared to the methyl or ethyl symmetrical derivatives in general provide better enantioselectivity in terms of both enantiomer resolution and number of separated chiral compounds, and show how the substitution pattern in positions 2 and 3 of the CD ring can influence the separation. Moreover, these new CD derivatives with better enantioselectivity are also shown to be very useful in routine analysis for the exhaustive control of samples containing several chiral characterizing markers in a single run. [Copyright &y& Elsevier]

Abstract: This study describes the development of a gas chromatography–mass spectrometry (GC–MS) library to identify optically active compounds in the flavour and fragrance field using enantioselective GC with cyclodextrin derivatives (CDs) as chiral selectors in combination with MS. The library operates on the “interactive” combination of linear retention indices (I T values) in parallel to MS spectra, so as to identify enantiomers reliably and to measure EE and/or ER unequivocally. Since MS is not a selective probe to discriminate optical isomers, mass spectra (or diagnostic ions in SIM mode) are used to locate the enantiomer(s) in the chromatogram, and I T values to identify it(them) safely and reliably in particular in complex mixtures. The library has been built up through the following steps: [(a)] Selection of CD derivatives able to cover a wide range of racemate separations. Four cyclodextrin derivatives were used: 2,6-di-O-methyl-3-O-pentyl-β-CD, 2,3-di-O-methyl-6-O-tert-butyldimethylsilyl-β-CD, 2,3-di-O-ethyl-6-O-tert-butyldimethylsilyl-β-CD, and 2,3-di-O-acetyl-6-O-tert-butyldimethylsilyl-β-CD. [(b)] Determination of the analytes’I T values and evaluation of their stability and reliability at both intra- and inter-laboratory level. [(c)] Determination of the range within which the I T of an enantiomer has to fall to be correctly identified, i.e. determination of a common retention index allowance (RIA). [(d)] Construction of the library, at the moment comprising the enantiomers of 134 racemates. A record has been attributed to each enantiomer including I T values determined on the four CD coated columns, mass spectrum, IUPAC chemical name, CAS number, molecular weight, and, when separated, racemate enantiomer resolution on the CD investigated. Some applications of the library are also reported. [Copyright &y& Elsevier]

• [P 66614 +][Cl−] and [P 66614 +][NTf 2 −] ionic liquids as GC stationary phases. • Unconventional selectivity but limited Maximum Allowable Operating Temperature (MOAT). • IL stationary phase immobilization increases the column MOAT. • Consistent performance and separation power of immobilized IL-based columns. • Complementary selectivity and retention of the two IL stationary phases. Phosphonium-based ionic liquids (ILs) have proven to be successful stationary phases (SPs) for gas chromatography (GC) in several fields of application because of their unique selectivity and good chromatographic properties. This study focuses on the use of two ILs as GC SPs that are based on the phosphonium derivatives trihexyl(tetradecyl)phosphonium chloride ([P 66614 +] [Cl−]), and trihexyl(tetradecyl)phosphonium bis[(trifluoromethyl)sulfonyl]imide ([P 66614 +][NTf 2 −]), which have previously been shown to be complementary in terms of chromatographic selectivity and retention. Their application in routine analysis has been limited by their lower maximum allowable operating temperatures (MAOT) (200 °C for the [P 66614 +][Cl−] IL and 180 °C for [P 66614 +][NTf 2 −]), which restricts their use to samples that consist of analytes with relatively high volatility. A previous study carried out in the Authors' laboratory focused on extending the use of the [P 66614 +][Cl−] IL SP to the analysis of samples with analytes of medium-to-low volatility by optimizing column characteristics and operative conditions. This study addresses the immobilization of both the [P 66614 +][Cl−] and [P 66614 +][NTf 2 −] ILs to the inner wall of fused silica columns to increase their MAOT under soft and hard reaction conditions. The resulting MAOT depended on more or less drastic immobilization conditions, and reached 220 °C for soft immobilization (So-Im) and 240 °C for hard immobilization (Ha-Im) in the [P 66614 +][Cl−] IL columns, and 200 °C for So-Im and 220° for Ha-Im in columns coated with the [P 66614 +] [NTf 2 −] IL. The influence of immobilization on the separation power and performance of all the columns has been evaluated using i) the Grob test, ii) a model mixture of 41 compounds of different polarity, structure, and with different organic functional groups representative of the flavor and fragrance field, iii) a standard mixture of 37 fatty acid methyl esters, iv) the peppermint essential oil, v) two mixtures of sesquiterpenic alcohols (farnesols and santalols), and vi) a standard mixture of 16 pesticides. These test samples were also used to demonstrate the complementarity of the two phosphonium-based IL SPs in terms of selectivity and retention. [ABSTRACT FROM AUTHOR]

Highlights • New GC stationary phases (SP) based on ionic liquids (ILs) with uncommon selectivity. • Ionic liquids with a phosphonium-based cation and different anions. • [P 66614 +] [Cl−] IL SP selectivity based on the analyte functional group. • [P 66614 +] [NTf 2 −] IL SP selectivity related to the analyte volatility and polarity. • Complementary selectivity for the flavor, fragrance and essential oil analyses. Abstract Room-temperature ionic liquids (ILs) have been shown to be successful as stationary phases (SPs) for gas chromatography in several fields of applications because of their unique and tunable selectivity, low vapor pressure and volatility, high thermal stability (over 300 °C), and good chromatographic properties. This study has been focused on two ILs based on a phosphonium cation (trihexyl(tetradecyl)phosphonium, P 66614) combined with different anions, previously shown to be suitable as gas chromatography (GC) SPs. In particular, trihexyl(tetradecyl)phosphonium bis[(trifluoromethyl)sulfonyl]imide ([P 66614 +] [NTf 2 −]) and trihexyl(tetradecyl)phosphonium chloride ([P 66614 +] [Cl−]) were investigated, as the Abraham linear solvation energy relationship has shown their ability to interact with the solute(s) when tested with a set of 26–34 probe analytes. The chromatographic performance were investigated on narrow bore and conventional test columns using the following: i) Grob test, ii) a group of model mixtures of compounds characteristic of the flavor, fragrance and essential oil fields (FFMix), iii) a standard mixture of 29 volatile allergens (AlMix), and iv) two essential oils of different complexity (sage and vetiver essential oils). The columns coated with the investigated IL SPs were characterized by similar polarity (Polarity Number (PN): 37 for [P 66614 +] [Cl−] and 33 for [P 66614 +] [NTf 2 −]), high efficiency and highly satisfactory inertness. The two IL SPs also exhibited a completely different separation performance, with [P 66614 +] [Cl−] test columns mainly characterized by high retention and selectivity based on the analyte functional groups, and [P 66614 +] [NTf 2 −] test columns featured by short retention and selectivity mainly related to the analyte volatility and polarity. These results were also confirmed with the analysis of sage and vetiver essential oils. [ABSTRACT FROM AUTHOR]

Comprehensive two-dimensional gas chromatography (GC × GC) coupled with Mass Spectrometry (MS) is one of today's most powerful analytical platforms for detailed analysis of medium-to-high complexity samples. The column set usually consists of a long, conventional-inner-diameter first dimension ( 1 D) (typically 15–30 m long, 0.32–0.25 mm d c ), and a short, narrow-bore second dimension ( 2 D) column (typically 0.5–2 m, 0.1 mm d c ) where separation is run in a few seconds. However, when thermal modulation is used, since the columns of a set are coupled in series, a flow mismatch occurs between the two dimensions, making it impossible to operate simultaneously at optimized flow conditions. Further, short narrow-bore capillaries can easily be overloaded, because of their lower loadability, limiting the effectiveness of 2 D separation. In this study, improved gas linear velocities in both chromatographic dimensions were achieved by coupling the 1 D column with two parallel 2 D columns, having identical inner diameter, stationary phase chemistry, and film thickness. In turn, these were connected to two detectors: a fast quadrupole Mass Spectrometer (MS) and a Flame Ionization Detector (FID). Different configurations were tested and performances compared to a conventional set-up; experimental results on two model mixtures ( n- alkanes and fourteen medium-to-high polarity volatiles of interest in the flavor and fragrance field) and on the essential oil of Artemisia umbelliformis Lam., show the system provides consistent results, in terms of analyte identification (reliability of spectra and MS matching) and quantitation, also affording an internal cross-validation of quantitation accuracy. [ABSTRACT FROM AUTHOR]

Highlights: [•] Thermodynamics of enantiomer Es-GC retention on cyclodextrin chiral selectors. [•] Measure of chromatographically meaningful parameters. [•] Entropy and enthalpy vs. characteristic temperature and thermal constant. [•] Optimum general heating rate in Es-GC: about 10°C per hold-up time. [ABSTRACT FROM AUTHOR]