Determination of volatile organic compounds by solid-phase microextraction—gas chromatography-differential mobility spectrometry

Up to now the analysis of aqueous samples by ion mobility spectrometry is a challenge due to the lack of suitable sample introduction systems. But just the introduction of asymmetric field strengths leading to a higher selectivity and sensitivity, this technique is of growing interest for on-site analysis of contaminated water. In this work, first results for the preparation of a portable GC-DMS system are presented. A differential mobility spectrometer (DMS) with a ⁶³Ni ionization source has been used as a detector for the gaschromatographic separation of benzene, toluene, ethylbenzene m-, o-, and p-xylene (BTEX) in water. Separation from the matrix and pre-concentration of the analytes was achieved by solid-phase microextraction (SPME). The influence of the different chromatographic parameters, extraction conditions and differential mobility spectrometry settings on the sensitivity and signal shape were investigated. Results of the optimization of the analytical method as well as analytical validation parameters such as method detection limit, limit of quantification and the repeatability are discussed. Additionally, the applicability of the method was demonstrated by the analysis of a real surface water sample.     

Use of solid-phase microextraction coupled to gas chromatography–mass spectrometry for determination of urinary volatile organic compounds in autistic children compared with healthy controls

Autism spectrum disorders (ASDs) are a group of neurodevelopmental disorders which have a severe life-long effect on behavior and social functioning, and which are associated with metabolic abnormalities. Their diagnosis is on the basis of behavioral and developmental signs usually detected before three years of age, and there is no reliable biological marker. The objective of this study was to establish the volatile urinary metabolomic profiles of 24 autistic children and 21 healthy children (control group) to investigate volatile organic compounds (VOCs) as potential biomarkers for ASDs. Solid-phase microextraction (SPME) using DVB/CAR/PDMS sorbent coupled with gas chromatography–mass spectrometry was used to obtain the metabolomic information patterns. Urine samples were analyzed under both acid and alkaline pH, to profile a range of urinary components with different physicochemical properties. Multivariate statistics techniques were applied to bioanalytical data to visualize clusters of cases and to detect the VOCs able to differentiate autistic patients from healthy children. In particular, orthogonal projections to latent structures discriminant analysis (OPLS-DA) achieved very good separation between autistic and control groups under both acidic and alkaline pH, identifying discriminating metabolites. Among these, 3-methyl-cyclopentanone, 3-methyl-butanal, 2-methyl-butanal, and hexane under acid conditions, and 2-methyl-pyrazine, 2,3-dimethyl-pyrazine, and isoxazolo under alkaline pH had statistically higher levels in urine samples from autistic children than from the control group. Further investigation with a higher number of patients should be performed to outline the metabolic origins of these variables, define a possible association with ASDs, and verify the usefulness of these variables for early-stage diagnosis.

Simultaneous analysis of 23 priority volatile compounds in water by solid-phase microextraction–gas chromatography–mass spectrometry and estimation of the method's uncertainty

Most water contaminations with volatile organic compounds (VOCs) are traceable to leaking underground fuel reservoirs, solvent storage vessels, agricultural practices, industrial residues, and deficient wastewater treatment and disposal. In order to perform effective monitoring of such organic micropollutants in a straightforward manner, a multiresidue method for the determination of 23 VOCs (trihalomethanes (THMs), BTEX and chlorinated solvents) in water has been developed using solid-phase microextraction (SPME) and capillary gas chromatography–mass spectrometry (GC–MS). This group includes also methyl-tert-butyl ether, epichlorhydrine, and vinyl chloride which present additional analytical difficulties. Three different fibres were assayed: 7-µm polydimethylsiloxane (PDMS), 100-µm PDMS, and 75-µm Carboxen-PDMS, and the extraction conditions were optimized. The best results for the majority of the analytes and mainly for those with the lowest signals were obtained using the Carboxen-PDMS fibre after 15 min of extraction in the headspace mode at a room temperature of 20 ± 2°C. The analytical sensitivity, linearity, precision, accuracy, and uncertainties have been studied for method validation in agreement with the international standard ISO/IEC 17025:2005. The limits of detection achieved with the proposed method (0.06–0.17 µg L^?1) are adequate to determine the VOCs at the restrictive levels established by the European legislation. This was a decisive achievement to enable the analysis of all VOCs listed under the drinking-water directive in a single assay. The method exhibits performance capabilities suitable for routine analysis of VOCs in drinking-water by quality-control laboratories as enforced by EU Directives. The method is currently being used for this purpose, and participation in proficiency tests was assessed, with encouraging results.     

Determination of carbamazepine in formulation samples using dispersive liquid–liquid microextraction method followed by ion mobility spectrometry

A simple, sensitive, fast and efficient method based on dispersive liquid–liquid microextraction (DLLME) followed by ion mobility spectrometry (IMS) has been proposed for preconcentration and trace detection of carbamazepine (CBZ) in formulation samples. In this method, 1 mL of methanol (disperser solvent) containing 80 μL of chloroform (extraction solvent) was rapidly injected by a syringe into a sample. After 5 min centrifugation, the preconcentrated carbamazepine in the organic phase was determined by IMS. Development of DLLME procedure includes optimization of parameters influencing the extraction efficiencies such as kind and volume of extraction solvent, disperser solvent and salt addition, centrifugation time and pH of the sample solution. The proposed method presented good linearity in the range of 0.05–10 μg mL^?1 and the detection limit was 0.025 μg mL^?1. The repeatability of the method expressed as relative standard deviation was 6 % (n = 5). This method has been applied to the analysis of carbamazepine formulation samples with satisfactory relative recoveries ≤75 %.     

Pre-concentration of phenolic compounds in water samples by novel liquid–liquid microextraction and determination by gas chromatography–mass spectrometry

Pre-concentration and determination of 8 phenolic compounds in water samples has been achieved by in situ derivatization and using a new liquid–liquid microextraction coupled GC–MS system. Microextraction efficiency factors have been investigated and optimized: 9 μL 1-undecanol microdrop exposed for 15 min floated on surface of a 10 mL water sample at 55 °C, stirred at 1200 rpm, low pH level and saturated salt conditions. Chromatographic problems associated with free phenols have been overcome by simultaneous in situ derivatization utilizing 40 μL of acetic anhydride and 0.5% (w/v) K₂CO₃. Under the selected conditions, pre-concentration factor of 235–1174, limit of detection of 0.005–0.68 μg/L (S/N = 3) and linearity range of 0.02–300 μg/L have been obtained. A reasonable repeatability (RSD ≤ 10.4%, n = 5) with satisfactory linearity (0.9995 ≥ r² ≥ 0.9975) of results illustrated a good performance of the present method. The relative recovery of different natural water samples was higher than 84%.     

Single-drop microextraction and gas chromatography–mass spectrometry for the determination of volatile aldehydes in fresh cucumbers

Headspace single-drop microextraction (HS-SDME) was used as a rapid and reliable method for the isolation and preconcentration of volatile aldehydes from fresh cucumbers. The utility of this methodology is demonstrated in the determination of (E)-2-nonenal and (E,Z)-2,6-nonadienal. The limit of detection, linearity and repeatability have been determined for 2,6-nonadienal and (E)-2-nonenal. Limits of detection for nonenal and nonadienal were 0.05 and 0.04 mg kg ⁻¹, respectively. The repeatability of extraction was obtained with the RSD values lower than 13%. Concentrations of target aldehydes in fresh cucumbers obtained by means of the HS-SDME method were in the range 9.4–12.5 (nonadienal) and 2.6–3.8 mg kg ⁻¹ (nonenal). The results of the single-drop extraction in combination with gas chromatography show promising potential for the analysis of volatile aldehydes in vegetables. Presented at the 11th International Conference on Chemistry and the Environment, 9-12 September 2007, Torun, Poland.     

Headspace solid-phase microextraction–gas chromatography–mass spectrometry for profiling free volatile compounds in Cabernet Sauvignon grapes and wines

The complex aroma of wine is derived from many sources, with grape-derived components being responsible for the varietal character. The ability to monitor grape aroma compounds would allow for better understanding of how vineyard practices and winemaking processes influence the final volatile composition of the wine. Here, we describe a procedure using GC–MS combined with headspace solid-phase microextraction (HS-SPME) for profiling the free volatile compounds in Cabernet Sauvignon grapes. Different sample preparation (SPME fiber type, extraction time, extraction temperature and dilution solvent) and GC–MS conditions were evaluated to optimize the method. For the final method, grape skins were homogenized with water and 8 ml of sample were placed in a 20 ml headspace vial with addition of NaCl; a polydimethylsiloxane SPME fiber was used for extraction at 40 °C for 30 min with continuous stirring. Using this method, 27 flavor compounds were monitored and used to profile the free volatile components in Cabernet Sauvignon grapes at different maturity levels. Ten compounds from the grapes, including 2-phenylethanol and β-damascenone, were also identified in the corresponding wines. Using this procedure it is possible to follow selected volatiles through the winemaking process.     

Characterization of volatile organic compounds and odors by in-vivo sampling of beef cattle rumen gas, by solid-phase microextraction, and gas chromatography–mass spectrometry–olfactometry

Volatile organic compounds (VOCs) and odors in cattle rumen gas have been characterized by in-vivo headspace sampling by solid-phase microextraction (SPME) and analysis by gas chromatography–mass spectrometry–olfactometry (GC–MS–O). A novel device enabling headspace SPME (HS-SPME) sampling through a cannula was designed, refined, and used to collect rumen gas samples from steers. A Carboxen–polydimethylsiloxane (PDMS) fiber (85 μm) was used for SPME sampling. Fifty VOCs from ten chemical groups were identified in the rumen headspace. The VOCs identified had a wide range of molecular weight (MW) (34 to 184), boiling point (−63.3 to 292 °C), vapor pressure (1.05 × 10⁻⁵ to 1.17 × 10² Pa), and water solubility (0.66 to 1 × 10⁶ mg L⁻¹). Twenty-two of the compounds have a published odor detection thresholds (ODT) of less than 1 ppm. More than half of the compounds identified are reactive and have an estimated atmospheric lifetime of <24 h. The amounts of VFAs, sulfide compounds, phenolic compounds, and skatole, and the odor intensity of VFAs and sulfide compounds in the rumen gas were all higher after feeding than before feeding. These results indicate that rumen gases can be an important potential source of aerial emissions of reactive VOCs and odor. In-vivo sampling by SPME then GC–MS–O analysis can be a useful tool for qualitative characterization of rumen gases, digestion, and its relationship to odor and VOC formation. Figure Modified cannula for rumen gas sampling with SPME     

Sampling of benzene in environmental and exhaled air by solid-phase microextraction and analysis by gas chromatography–mass spectrometry

Benzene is classified as a Group I carcinogen by the International Agency for Research on Cancer (IARC). The risk assessment for benzene can be performed by monitoring environmental and occupational air, as well as biological monitoring through biomarkers. The present work developed and validated methods for benzene analysis by GC/MS using SPME as the sampling technique for ambient air and breath. The results of the analysis of air in parks and avenues demonstrated a significant difference, with average values of 4.05 and 18.26 μg m⁻³, respectively, for benzene. Sampling of air in the occupational environment furnished an average of 3.41 and 39.81 μg m⁻³. Moreover, the correlations between ambient air and expired air showed a significant tendency to linearity (R ² = 0.850 and R ² = 0.879). The results obtained for two groups of employees (31.91 and 72.62 μg m⁻³) presented the same trend as that from the analysis of environmental air.     

A new method for the synthesis of organic–polyoxometallate hybrid compounds

The reaction of the Na₂MoO₄ or Na₂WO₄ salt with organic amine and PCl₅, SiCl₄ or TiCl₄ in hydrochloric acid medium under hydrothermal conditions yields organic–polyoxometallate hybrid compounds, with the following reaction formula: Na₂MO₄ + Lewis-base + XCl_n + HCl → (Lewis-baseH)_m(XM₁₂O₄₀) + NaCl + H₂O (M = Mo or W; X = P, Si, Ti,; n = 3–5). By using this method, four new complexes, [(CH₃)₂NH]₃[H₃PW₁₂O₄₀] (1), (C₂H₅OH)₃(H₃PMo₁₂O₄₀) (2), [DMDA]₂[H₄SiW₁₂O₄₀]·H₂O (3) (DMDA = 1 N,3 N-dimethyl-1,3-diazolidine) and [(DAN)₆][H₄TiW₁₂O₄₀]·4H₂O (DAN = 4,4′-dianiline) (4), were obtained, and their crystal structures are reported. Thermal analysis of 1, 2 and 4 has been carried out. The thermal analysis indicates that the Keggin anion skeleton begins to decompose at about 300 °C. The possibility of constructing hydrogen-bond interactions by association between the polyoxometallate and the organic compound is explored. The roles of solvents and organic groups in the formation of specific crystalline architectures are discussed. The crystal structure of [H₄TiW₁₂O₄₀], a hetero-transition-metal Keggin polyoxometallate with a square-plane TiO₄, has been reported. Four architectures developed by hydrogen-bond associations of different Keggin polyoxometallates and organic bearing N–H or O–H donor functions are described. The selected organic modules (4,4′-dianiline, 1,3-dimethylimidazolidine, dimethylamine and ethanol) possess hydrogen-donor functions to allow them to act as bridges between polyoxometallate groups. Depending on the nature of the donor group, the number of hydrogens available for bonding, the geometric features and the sizes of the organic modules, diverse assembling patterns have been observed ranging from one-dimensional to three-dimensional networks. For all the networks, H₃O⁺ and H⁺ act as actual linkers between the molecular units.     

A reliable and simple method for the assay of neuroendocrine tumor markers in human urine by solid-phase microextraction–gas chromatography-triple quadrupole mass spectrometry

Homovanillic acid (HVA), vanylmandelic acid (VMA), and 5-hydroxyindoleacetic acid (5-HIAA) are the metabolites of some catecholamines such as epinephrine, nor-epinephrine, dopamine and serotonin and their quantification is used in the diagnosis and management of patients with neurocrine tumors. A novel approach in the assay of these biomarkers in human urine samples by solid phase microextraction (SPME) combined with gas chromatography-triple quadrupole mass spectrometry (GC–QqQ-MS) is presented. A preliminary derivatization with ethyl chloroformate/ethanol was used and the corresponding derivatives were then extracted by SPME in immersion mode. The performance of five SPME fibers and three chloroformates were evaluated in univariate mode and the best results were obtained using the polyacrylate fiber and ethyl chloroformate. The variables affecting the efficiency of SPME analysis were optimized by the multivariate approach of “Experimental design” and, in particular, a central composite design (CCD) was applied. The optimum working conditions in terms of response values were achieved by performing analysis at room temperature with addition of NaCl (9.5%) and with an extraction time of 25.8 min. Identification and quantification of analytes were carried out by using a gas chromatography-triple quadrupole mass spectrometry (GC–QqQ MS) system in multiple reaction monitoring (MRM) acquisition. An evaluation of all analytical parameters shows that the proposed method provides satisfactory results. Very good linearities were, in fact, achieved in the tested calibration ranges with correlation coefficient values >0.99 for all the analytes and accuracies and RSDs calculated for between-run and tested at concentrations of 1, 10, and 80 mg L⁻¹ were ranging from 91.3% to 106.6%, and from 0.5 to 8.9%, respectively. Moreover, the LOD values obtained can be considered very satisfactory (1.3, 0.046 and 24.3 μg L⁻¹ for HVA, VMA and 5-HIAA, respectively). The developed protocol represents, therefore, a simple, rapid and selective tool for assaying these acidic biomarkers in urine samples for neuroendocrine cancer diagnosis.     

A headspace solid-phase microextraction procedure coupled with gas chromatography–mass spectrometry for the analysis of volatile polycyclic aromatic hydrocarbons in milk samples

A sensitive and solvent-free method for the determination of ten polycyclic aromatic hydrocarbons, namely, naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benzo[a]anthracene and chrysene, with up to four aromatic rings, in milk samples using headspace solid-phase microextraction and gas chromatography–mass spectrometry detection has been developed. A polydimethylsiloxane–divinylbenzene fiber was chosen and used at 75°C for 60 min. Detection limits ranging from 0.2 to 5 ng L⁻¹ were attained at a signal-to-noise ratio of 3, depending on the compound and the milk sample under analysis. The proposed method was applied to ten different milk samples and the presence of six of the analytes studied in a skimmed milk with vegetal fiber sample was confirmed. The reliability of the procedure was verified by analyzing two different certified reference materials and by recovery studies. Figure Milk is safe, healthy food     

Development of a method for metabolomic analysis of human exhaled breath condensate by gas chromatography–mass spectrometry in high resolution mode

Exhaled breath condensate (EBC) is a promising biofluid scarcely used in clinical analysis despite its non-invasive sampling. The main limitation in the analysis of EBC is the lack of standardized protocols to support validation studies. The aim of the present study was to develop an analytical method for analysis of human EBC by GC–TOF/MS in high resolution mode. Thus, sample preparation strategies as liquid–liquid extraction and solid-phase extraction were compared in terms of extraction coverage. Liquid–liquid extraction resulted to be the most suited sample preparation approach providing an average extraction efficiency of 77% for all compounds in a single extraction. Different normalization approaches were also compared to determine which strategy could be successfully used to obtain a normalized profile with the least variability among replicates of the same sample. Normalization to the total useful mass spectrometry signal (MSTUS) proved to be the most suited strategy for the analysis of EBC from healthy individuals (n = 50) reporting a within-day variability below 7% for the 51 identified compounds and a suited data distribution in terms of percentage of metabolites passing the Skewness and Kurtosis test for normality distribution. The composition of EBC was clearly dominated by the presence of fatty acids and derivatives such as methyl esters and amides, and volatile prenol lipids. Therefore, EBC offers the profile of both volatile and non-volatile components as compared to other similar biofluids such as exhaled breath vapor, which only provides the volatile profile. This human biofluid could be an alternative to others such as serum/plasma, urine or sputum to find potential markers with high value for subsequent development of screening models.     

Determination of volatile oak compounds in aged wines by multiple headspace solid-phase microextraction and gas chromatography–mass spectrometry (MHS-SPME–GC–MS)

Multiple headspace solid-phase microextraction (MHS-SPME) with gas chromatography–mass spectrometry is proposed for quantification of nine volatile oak compounds in aged wines. These compounds are formed and extracted by wine when it is matured in oak barrels and are responsible for particular organoleptic properties and the high quality of these wines. Some important variables of the extraction process, for example volume of sample and extraction time, were studied. Extraction of 50 μL wine was performed with a divinylbenzene–Carboxen–polydimethylsiloxane fibre at 55 °C for 60 min. For calibration the same conditions were used, except that the wine was substituted by 50 μL of a standard solution in synthetic wine. The linearity, detection limits, and repeatability of the method were determined by use of standard solutions in synthetic wine. Detection limits were between 0.01 and 10 μg L⁻¹ (for eugenol and furfural, respectively) and repeatability, expressed as relative standard deviation, was from 2 to 6%. The method was used to analyse six red wines and the concentrations obtained were statistically compared with those obtained by the standard addition method for the same wines.     

At-line microextraction by packed sorbent-gas chromatography–mass spectrometry for the determination of UV filter and polycyclic musk compounds in water samples

An at-line analysis protocol is presented that allows the determination of four UV filters, two polycyclic musk compounds and caffeine in water at concentration level of ng L⁻¹. The fully automated method includes analytes enrichment by Microextraction by packed sorbent (MEPS) coupled directly to large volume injection-gas chromatography–mass spectrometry. Two common SPE phases, C8 and C18, were examined for their suitability to extract the target substances by MEPS. The analytes were extracted from small sample volumes of 800 μL with recoveries ranging from 46 to 114% for the C8-sorbent and 65–109% for the C18-sorbent. Limits of detection between 34 and 96 ng L⁻¹ enable the determination of the analytes at common environmental concentration levels. Both sorbents showed linear calibration curves for most of the analytes up to a concentration level of 20 ng mL⁻¹. Carryover was minimized by washing the sorbents 10 times with 100 μL methanol. After this thorough cleaning, the MEPS are re-used and up to 70 analyses can be performed with the same sorbent. The fully automated microextraction GC–MS protocol was evaluated for the influence of matrix substances typical for wastewater. Dilution of samples prior to MEPS is recommended when the polar caffeine is present at high concentration. Real water samples were analyzed by the MEPS-GC–MS method and compared to standard SPE.     

Development of a fast liquid chromatography–tandem mass spectrometry method for the determination of endocrine-disrupting compounds in waters

A fast liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS-MS) method was developed to study five endocrine-disrupting compounds (4-n-nonylphenol, bisphenol A, estrone, 17β-estradiol and 17α-ethinylestradiol) in water. Different columns were tested; the chromatographic separation of the analytes was optimized on a Pinnacle DB biphenylic column with a water–acetonitrile gradient elution, which allowed the separation of the selected endocrine-disrupting compounds (EDCs) in less than 6 min. Quantitative analysis was performed in selected reaction monitoring (SRM) mode; two transitions were chosen for each compound, using the most abundant for quantitation. Calibration curves using bisphenol A-d ₁₆ as internal standard were drawn, showing good correlation coefficients (0.9993–0.9998). All figures of merit of the method were satisfactory; limits of detection were in the low pg range for all analytes. The method was then applied to the determination of the analytes in real water samples: to this aim, polar organic chemical integrative samplers (POCIS) were deployed in the influent and in the effluent of a drinking water treatment plant in Liguria (Italy). The EDC level was rather low in the influent and negligible in the outlet, reflecting the expected function of the treatment plant.     

A novel method of liquid chromatography–tandem mass spectrometry combined with chemical derivatization for the determination of ribonucleosides in urine

Ribonucleosides are the end products of RNA metabolism. These metabolites, especially the modified ribonucleosides, have been extensively evaluated as cancer-related biomarkers. However, the determination of urinary ribonucleosides is still a challenge due to their low abundance, high polarity and serious matrix interferences in urine samples. In this study, a derivatization method based on a chemical reaction between ribonucleosides and acetone to form acetonides was developed for the determination of urinary ribonucleosides. The derivative products, acetonides, were detected by using liquid chromatography–tandem mass spectrometry (LC–MS/MS). The methodological evaluation was performed by quantifying four nucleosides for linear range, average recovery, precision, accuracy and stability. The validated procedures were applied to screen modified ribonucleosides in urine samples. Improvement of separation and enhancement of sensitivity were obtained in the analysis. To identify ribonucleosides, inexpensive isotope labeling acetone (acetone-d₆) and label-free acetone were applied to form ordinary and deuterated acetonides, respectively. The two groups of samples were separated with orthogonal partial least squares (OPLS). The ordinary and deuterated pairs of acetonides were symmetrically distributed in the S-plot for easy and visual signal identification. After structural confirmation, a total of 56 ribonucleosides were detected, 52 of which were modified ribonucleosides. The application of derivatization, deuterium-labeling and multivariate statistical analysis offers a new option for selective detection of ribonucleosides in biological samples.     

Particle-into-liquid sampler on-line coupled with solid-phase extraction-liquid chromatography–mass spectrometry for the determination of organic acids in atmospheric aerosols

In the present study, sample collection and preparation were directly integrated with a chromatographic system by coupling a particle-into-liquid sampler for the first time on-line with solid-phase extraction-liquid chromatography–tandem mass spectrometry. Several organic acids, such as adipic, hydroxyglutaric, mandelic, vanillic, cis-pinonic, pinic, azelaic and sebacic, were used in the research. For sample pretreatment and concentration, strong anion exchange material was used in the extraction. Sampling, extraction and analysis conditions were optimized to obtain reliable information about aerosol chemical composition. To evaluate the performance of the on-line coupled system, half of each sample was analysed on-line and the other half was derivatized and analysed off-line by gas chromatography–mass spectrometry. Comparison of the two techniques with use of t-test showed the results to be in an excellent agreement. Limits of detection of studied acids in on-line system were between 0.1 and 0.9 ng. The on-line coupled system is fast and reliable and a promising tool for the real time analysis of organic acids in atmospheric aerosols.     

Hollow fiber-based liquid–liquid–liquid microextraction combined with electrospray ionization-ion mobility spectrometry for the determination of pentazocine in biological samples

A new method based on liquid–liquid–liquid microextraction combined with electrospray ionization-ion mobility spectrometry (LLLME-ESI-IMS) was used for the determination of pentazocine in urine and plasma samples. Experimental parameters which control the performance of LLLME, such as selection of composition of donor and acceptor phase, type of organic solvent, ionic strength of the sample, extraction temperature and extraction time were studied. The limit of detection and relative standard deviation of the method were 2 ng/mL and 5.3%, respectively. The linear calibration ranged from 10 to 500 ng/mL with r² = 0.998. Pentazocine was successfully determined in urine and plasma samples without any significant matrix effect.     

Headspace solid-phase microextraction combined with GC×GC-TOFMS for the analysis of volatile compounds of Coptis species rhizomes

In this study, the investigation of the volatile compounds of dried rhizomes of Coptis chinensis Franch, C. deltoidea C. Y. Cheng et Hsiao, and C. teeta Wall was carried out to complete the chemical composition of these valuable natural products. Volatile profiles were established and compared after headspace solid-phase microextraction (HS-SPME) using a polydimethylsiloxane/divinylbenzene (PDMS/DVB, 65 μm) fibre coupled to comprehensive 2D gas chromatography time-of-flight mass spectrometry (GC×GC-TOFMS). Analyses were performed and compared on two column-phase combinations (non-polar/polar and polar/non-polar). The majority of the identified compounds eluted as well-separated (pure) components as a result of high-resolution capability of the GC×GC method, which significantly reduces co-elution. Therefore, this increases the likelihood that pure mass spectra can be obtained. More than 290 volatile and semi-volatile organic compounds were tentatively characterized by means of GC×GC in tandem with TOFMS detection. Improved result interpretations were obtained in terms of compound classification based on the organized structure of the peaks of structurally related compounds in the GC×GC contour plot. These compounds are distributed over the chemical groups of hydrocarbons, acids, alkenes, alkynes, aldehydes, ketones, alcohols, esters, furans, and terpenoids. Among all the chemical groups, terpenoids present the higher number of identified compounds (44), alkenes (41), and aldehydes and ketones (28). This study completed the volatile phytochemical analysis of the headspace composition of various Coptis species rhizomes, and should serve as a means to identify the difference between the rhizomes and may also be useful to confirm individual species based on their volatile chemical profile.