Rapid headspace solid-phase microextraction-gas chromatographic-time-of-flight mass spectrometric method for qualitative profiling of ice wine volatile fraction. III. Relative characterization of Canadian and Czech ice wines using self-organizing maps

The determination of volatile and semi-volatile components of ice wine aroma was realized throughout the development of a rapid headspace solid-phase microextraction-gas chromatography-time-of-flight mass spectrometry (SPME-GC-TOF-MS) analytical method (Part I) and its application to the analysis of 137 samples produced in Canada and Czech Republic and collected directly from the producing wineries (Part II). In this Part III study, the complex matrix resulting from the analysis of the 58 compounds selected for each sample as described in Part II, was submitted to critical interpretation by using a self-organizing map (SOM) technique. Results were commented in terms of relative characterization of samples according to their geographical origin, grape varieties, and vintage years. When clear clustering was obtained, the most determinant compounds responsible for the observed differentiations were identified and further discussed.     

Rapid headspace solid-phase microextraction-gas chromatographic-time-of-flight mass spectrometric method for qualitative profiling of ice wine volatile fraction. II: Classification of Canadian and Czech ice wines using statistical evaluation of the data

The previously developed and optimized headspace solid-phase microextraction (HS-SPME)-GC-time-of-flight (TOF) MS analytical method for the determination of compounds with a wide range of polarities and volatilities was successfully used in this study to characterize and classify a large set of ice wines according to their origin, grape variety and oak or stainless steel fermentation/ageing conditions, based on a statistical evaluation (principal component analysis (PCA)) of the measured data. More than 130 ice wine samples collected directly from Canadian and Czech wine producers were analyzed in this study. The SPME step was beneficially carried out utilizing the new-generation super elastic divinylbenzene/Carboxen/polydimethylsiloxane (DVB/CAR/PDMS) 50 microm/30 microm fiber assembly. One fiber was used for the whole sequence of ice wine samples, control and blank experiments, which consisted of more than 600 individual extraction/injection cycles. Utilizing the high-speed TOF analyzer, full spectral information within the range of 35-450 u was collected for the entire GC run (as short as 4.5 min) without compromising in the detection sensitivity, as compared to other scanning mass analyzers operated in selected ion monitoring or MS(n) mode to achieve similar sensitivity. The identification of analytes was performed by a combination of the linear temperature-programmed retention index (LTPRI) approach with the comparison of the obtained spectra with three libraries included in the ChromaTOF software. A total of 201 peaks were tentatively assigned as ice wine aroma components and 58 of those compounds were evaluated in all of the examined samples.     

Headspace solid-phase microextraction-gas chromatographic-time-of-flight mass spectrometric methodology for geographical origin verification of coffee

Increasing consumer awareness of food safety issues requires the development of highly sophisticated techniques for the authentication of food commodities. The food products targeted for falsification are either products of high commercial value or those produced in large quantities. For this reason, the present investigation is directed towards the characterization of coffee samples according to the geographical origin. The conducted research involves the development of a rapid headspace solid-phase microextraction (HS-SPME)-gas chromatography-time-of-flight mass spectrometry (GC-TOFMS) method that is utilized for the verification of geographical origin traceability of coffee samples. As opposed to the utilization of traditional univariate optimization methods, the current study employs the application of multivariate experimental designs to the optimization of extraction-influencing parameters. Hence, the two-level full factorial first-order design aided in the identification of two influential variables: extraction time and sample temperature. The optimum set of conditions for the two variables was 12 min and 55 degrees C, respectively, as directed by utilization of Doehlert matrix and response surface methodology. The high-throughput automated SPME procedure was completed by implementing a single divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS) 50/30 microm metal fiber with excellent durability properties ensuring the completion of overall sequence of coffee samples. The utilization of high-speed TOFMS instrument ensured the completion of one GC-MS run of a complex coffee sample in 7.9 min and the complete list of benefits provided by ChromaTOF software including fully automated background subtraction, baseline correction, peak find and mass spectral deconvolution algorithms was exploited during the data evaluation procedure. The combination of the retention index (RI) system using C(8)-C(40) alkanes and the mass spectral library search was utilized for the confirmation of analyte identity in the reference authentic Brazilian coffee sample. The semi-quantitative results were then submitted to statistical evaluation, namely principal component analysis (PCA) for the establishment of geographical origin discriminations.     

Screening of volatile composition from Portuguese multifloral honeys using headspace solid-phase microextraction-gas chromatography-quadrupole mass spectrometry

The volatile composition from four types of multifloral Portuguese (produced in Madeira Island) honeys was investigated by a suitable analytical procedure based on dynamic headspace solid-phase microextraction (HS-SPME) followed by thermal desorption gas chromatography-quadrupole mass spectrometry detection (GC-qMS). The performance of five commercially available SPME fibres: 100 μm polydimethylsiloxane, PDMS; 85 μm polyacrylate, PA; 50/30 μm divinylbenzene/carboxen on polydimethylsiloxane, DVB/CAR/PDMS (StableFlex); 75 μm carboxen/polydimethylsiloxane, CAR/PDMS, and 65 μm carbowax/divinylbenzene, CW/DVB; were evaluated and compared. The highest amounts of extract, in terms of the maximum signal obtained for the total volatile composition, were obtained with a DVB/CAR/PDMS coating fibre at 60 °C during an extraction time of 40 min with a constant stirring at 750 rpm, after saturating the sample with NaCl (30%). Using this methodology more than one hundred volatile compounds, belonging to different biosynthetic pathways were identified, including monoterpenols, C₁₃-norisoprenoids, sesquiterpenes, higher alcohols, ethyl esters and fatty acids. The main components of the HS-SPME samples of honey were in average ethanol, hotrienol, benzeneacetaldehyde, furfural, trans-linalool oxide and 1,3-dihydroxy-2-propanone.     

Development of a headspace solid-phase microextraction-gas chromatography-mass spectrometry method for the identification of odour-causing volatile compounds in packaging materials

A method for the identification of volatile organic compounds in packaging materials is presented in this study. These compounds are formed by thermooxidative degradation during the extrusion coating process in the manufacture of packaging. Headspace solid-phase microextraction (HS-SPME) was used as sample preparation technique prior to the determination of the volatile organic compounds by gas chromatography-mass spectrometry (GC-MS). The effects of extraction variables, such as the type of fibre, the incubation temperature, the pre-incubation time, the size of the vial and the extraction time on the amounts of the extracted volatile compounds were studied. The optimal conditions were found to be: carboxen-polydimethylsiloxane 75 microm fibre, 5 min of pre-incubation time, 100 degrees C of incubation temperature, 20-ml vial, and 15 min of extraction time. The chromatograms obtained by HS-SPME and static headspace extraction were compared in order to show that the HS-SPME method surpasses the static headspace method in terms of sensitivity. Twenty-five compounds were identified including carbonyl compounds (such as 3-methyl-butanal, 3-heptanone or octanal), carboxylic acids (such as pentanoic acid or hexanoic acid) known as odour causing compounds and hydrocarbons (such as decane, undecane or dodecane). Finally, the method was applied to different packaging samples (one odour-unacceptable, two odour-acceptable, and three odourless samples) and to the raw materials in order to find out the odour-responsible volatile organic compounds and their source.     

Simultaneous analysis of thiols, sulphides and disulphides in wine aroma by headspace solid-phase microextraction-gas chromatography.

This paper deals with the improvement of a headspace solid-phase microextraction (HS-SPME) method, developed in a previous work, in order to analyse, simultaneously, thiols, sulphides and disulphides in wines. This can be achieved by applying Carboxen-polydimethylsiloxane fibres and a cryogenic trap to focus the analytes. Under optimum conditions, the HS-SPME procedure developed shows low limits of detection for the sulphides and disulphides studied (0.05-3 micrograms/l) and the thiols can also be analysed and detected at very low levels (0.5-1 microgram/l) with acceptable recoveries and repeatability.     

Optimisation of headspace solid-phase microextraction for the analysis of volatile phenols in wine

Headspace solid-phase microextraction has been applied to the analysis of volatile phenols in wine. Silica fibre coated with Carbowax-divinylbenzene was found to be more efficient at extracting these compounds than other fibres such as those coated with polydimethylsiloxane, polyacrylate, carboxen-polydimethylsiloxane, and polydimethylsiloxane-divinylbenzene. Different parameters such as extraction time, temperature of the sample during the extraction, ionic strength and sample volume were optimised using a two-level factorial design expanded further to a central composite design, in order to evaluate several possibly influential and/or interacting factors. The headspace (HS)-SPME procedure developed shows adequate detection and quantitation limits, and linear ranges for correctly analysing these compounds in wine. The recoveries obtained were close to 100%, with repeatability values lower than 16%. The method was applied to a variety of white and red wines.     

Headspace solid-phase microextraction-gas chromatography-quadrupole mass spectrometric methodology for the establishment of the volatile composition of Passiflora fruit species

Dynamic headspace solid-phase microextraction (HS-SPME) followed by thermal desorption gas chromatography-quadrupole mass spectrometry analysis (GC-_qMS), was used to investigate the aroma profile of different species of passion fruit samples. The performance of five commercially available SPME fibres: 65 μm polydimethylsiloxane/divinylbenzene, PDMS/DVB; 100 μm polydimethylsiloxane, PDMS; 85 μm polyacrylate, PA; 50/30 μm divinylbenzene/carboxen on polydimethylsiloxane, DVB/CAR/PDMS (StableFlex); and 75 μm carboxen/polydimethylsiloxane, CAR/PDMS; was evaluated and compared. Several extraction times and temperature conditions were also tested to achieve optimum recovery. The SPME fibre coated with 65 μm PDMS/DVB afforded the highest extraction efficiency, when the samples were extracted at 50 °C for 40 min with a constant stirring velocity of 750 rpm, after saturating the sample with NaCl (17%, w/v — 0.2 g). A comparison among different passion fruit species has been established in terms of qualitative and semi-quantitative differences in volatile composition. By using the optimal extraction conditions and GC-qMS it was possible to tentatively identify seventy one different compounds in Passiflora species: 51 volatiles in Passiflora edulis Sims (purple passion fruit), 24 in P. edulis Sims f. flavicarpa (yellow passion fruit) and 21 compounds in Passiflora mollissima (banana passion fruit). It was found that the ethyl esters comprise the largest class of the passion fruit volatiles, including 82.8% in P. edulis variety, 77.4% in P. edulis Sims f. flavicarpa variety and 39.9% in P. mollissima.The semi-quantitative results were then submitted to principal component analysis (PCA) in order to establish relationships between the compounds and the different passion fruit species under investigation.     

Rapid headspace solid-phase microextraction/gas chromatographic/mass spectrometric assay for the quantitative determination of some of the main odorants causing off-flavours in wine

In this study we present a rapid and simultaneous assay method using headspace (HS) solid-phase microextraction (SPME)/gas chromatography (GC)/electron impact (EI) mass spectrometry (MS) (selected ion monitoring) for contaminants causing the principal organoleptic defects of wine (2,4,6-trichloroanisole, 2,3,4,6-tetrachloroanisole, pentachloroanisole, 2,4,6-tribromoanisole, 1-octen-3-ol, geosmin, 2-methylisoborneol, 3-isopropyl-2-methoxypyrazine, fenchol, fenchone, 2-methoxy-3,5-dimethylpyrazine, 4-ethylphenol, 4-ethylguaiacol, 4-vinylphenol, 4-vinylguaiacol, 3-isobutyl-2-methoxypyrazine, guaiacol and ethyl acetate). The method was validated according to protocols NF ISO 5725-1, 2 and NF V03-110. Its characteristics (limit of detection (LOD), limit of quantification (LOQ), uncertainties) were determined after having optimised the SPME parameters. The target contaminants were quantified in the wines below their threshold of perception with a satisfactory relative standard deviation for all the analytes except ethyl acetate (RSD=36%); for that, the assay method permits clear differentiation of the wines that are at risk of presenting an acescent character, i.e. containing more than 120mgL(-1) ethyl acetate. The target volatile and odorous substances were determined at concentrations significantly below their threshold of perception in a hydroalcoholic context and their threshold of recovery in wines.     

Method optimization by solid-phase microextraction in combination with gas chromatography with mass spectrometry for analysis of beer volatile fraction

A simple and sensitive method for the analysis of beer volatile compounds was optimised using headspace solid-phase microextraction (SPME) and gas chromatography with mass detection. Headspace SPME using a 75 microm Carboxen-polydimethylsiloxane (CAR-PDMS) fiber provided effective sample enrichment and enabled extraction of a wide variety of compounds. The reproducibility depended on the compounds, with a mean value of 1.4% for alcohols, 3.3% for ethers, 6.7% for aldehydes, 3.4% for acids, 1.7% for aromatic compounds, 2.4% for esters, 7.4% for hydrocarbons, 1.8% for alicyclic compounds, and 3.4% for heterocyclic compounds. The optimised methodology can be used to compare volatile profile from different types of beers and eventually to study the evolution of a particular beer during aging.     

Development of a sensitive non-targeted method for characterizing the wine volatile profile using headspace solid-phase microextraction comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry

Future understanding of differences in the composition and sensory attributes of wines require improved analytical methods which allow the monitoring of a large number of volatiles including those present at low concentrations. This study presents the optimization and application of a headspace solid-phase microextraction (HS-SPME) method for analysis of wine volatiles by comprehensive two-dimensional gas chromatography (GC×GC) time-of-flight mass spectrometry (TOFMS). This study demonstrates an important advancement in wine volatile analysis as the method allows for the simultaneous analysis of a significantly larger number of compounds found in the wine headspace compared to other current single dimensional GC-MS methodologies. The methodology allowed for the simultaneous analysis of over 350 different tentatively identified volatile and semi-volatile compounds found in the wine headspace. These included potent aroma compound classes such as monoterpenes, norisoprenoids, sesquiterpenes, and alkyl-methoxypyrazines which have been documented to contribute to wine aroma. It is intended that wine aroma research and wine sensory research will utilize this non-targeted method to assess compositional differences in the wine volatile profile.     

Sample preparation optimization in wine and grapes. Dilution and sample/headspace volume equilibrium theory for headspace solid-phase microextraction

Most headspace solid-phase microextraction (HS-SPME) volatile analysis methods have been developed for aqueous samples and have been either adapted or applied to complex matrices. This study examines sample/headspace equilibrium based on realistic (non-spiked) concentration levels in real complex sample matrices (grapes and wine) with a systematic multivariate statistical approach. The presence and absence of matrix effects are explained through exponential and linear relationships, respectively. The potential of over- and underestimating volatile compounds in a diluted sample is illustrated and the common dilution equation (C1V1=C2V2) is shown to not always apply to headspace volatile analysis. Additionally, sample dilution was shown to be more sensitive to matrix effects than sample/headspace volume variations with the latter showing analyte dependency. An optimum sample size of 6.9-8.6g in a 20mL vial without dilution was observed. This study shows that sensitivity and limit of detection (LOD) can be improved to a limit with a subsequent loss - an extension to existing theory. The study further illustrates that in trying to bring an analyte within linear range through sample dilution, sensitivity and LOD can be lost with a probable shift in optimum ranges and sample/headspace equilibrium.     

Determination of minor and trace volatile compounds in wine by solid-phase extraction and gas chromatography with mass spectrometric detection

A new method for the quantitative determination of important wine odorants has been developed. The wine (50 ml) is extracted in a 200 mg solid-phase extraction (SPE) cartridge filled with Lichrolut-EN resins from Merck. The elution is carried out with 1.3 ml of dichloromethane. These extracts are directly analyzed by GC-Ion Trap-MS without further concentration. Twenty-seven important wine odorants, such as volatile phenols, vanillin derivatives, aliphatic lactones, nor-isoprenoids, minor esters and terpenols, can be quantitatively determined in a single gas chromatography-mass spectrometry (GC-MS) run. The recoveries in the SPE isolation are in good agreement with those expected from the calculation of breakthrough volumes from solid-liquid distribution coefficients and are higher than 90%, except for guaiacol, vanillin, 2,6-dimethoxyphenol and 4-vinylphenol. In most cases, precision is below 10%. Method linearity is satisfactory, with r2 higher than 0.99 in all cases. The analysis of spiked samples has shown that there is good agreement between the real mass of compound added to the wine and that determined by analysis. In all cases detection limits are below the odor detection threshold of the compounds, and the calibrated interval covers the natural range of occurrence of the compounds in wine.     

Determination of volatile oak compounds in wine by headspace solid-phase microextraction and gas chromatography-mass spectrometry

A headspace solid-phase microextraction (HS-SPME) and gas chromatography (GC) coupled to mass spectrometry (MS) method was developed to identify and quantify 14 volatile oak compounds in aged red wines. The most important HS-SPME variables were optimised by experimental design technique in order to improved the extraction process. The selected conditions were: 10 mL of sample in 20 mL sealed vials with addition of 30% of sodium chloride (saturated solution), divinylbenzene-carboxen-polydimethylsiloxane (DVB-CAR-PDMS) fibre, 10 min of pre-incubation time, 70 degrees C of temperature and 60 min of extraction time without agitation. The features of the method were established for the studied compounds in terms of linear range, slope and intercept of the calibration graphs, detection and quantification limits and repeatability. For all compounds detection limits were below their threshold levels and repeatability, in terms of relative standard deviation, was good, with values between 3 and 11%. Finally, the method was applied to the analysis of six aged red wines by both internal standard and standard addition calibration methods. The concentrations obtained with both methods were statistically compared.     

Development of headspace solid-phase microextraction-gas chromatography method for the determination of solvent residues in edible oils and pharmaceuticals

The application of headspace solid-phase microextraction for isolation and enrichment of solvent residues from oils and pharmaceuticals is discussed. The optimal parameters for isolation and preconcentration of common process solvents (hexane, benzene, toluene and selected chloroderivatives of hydrocarbons) were established. Four fiber types (100 microm polydimethylsiloxane (PDMS), 75 microm Carboxen-PDMS, 65 microm PDMS-divinylbenzene and 85 microm polyacrylate) were evaluated to choose the most efficient coating, able to absorb the greatest amount of analytes. GC-flame ionization detection (FID) and GC-electron-capture detection systems were used for quantitative and qualitative analysis, adequately to the appropriate group of the analytes. For all compounds the limit of detection (LOD), linearity, dynamic range, repeatability and intermediate precision were estimated.     

Analysis of virgin olive oil volatile compounds by headspace solid-phase microextraction coupled to gas chromatography with mass spectrometric and flame ionization detection

The efficiency of headspace solid-phase microextraction (SPME) was evaluated for the qualitative and semi-quantitative analysis of virgin olive oil volatile compounds. The behaviour of four fibre coatings was compared for sensitivity, repeatability and linearity of response. A divinylbenzene-Carboxen-polydimethylsiloxane fibre coating was found to be the most suitable for the analysis of virgin olive oil volatiles. Sampling and chromatographic conditions were examined and the SPME method, coupled to GC with MS and flame ionization detection, was applied to virgin olive oil samples. More than 100 compounds were isolated and characterised. The presence of some of these compounds in virgin olive oil has not previously been reported. The main volatile compounds present in the oil samples were determined quantitatively.     

A new method for the determination of short-chain fatty acids from the aliphatic series in wines by headspace solid-phase microextraction-gas chromatography-ion trap mass spectrometry

A new analytical method for the determination of nine short-chain fatty acids (acetic, propionic, isobutyric, butyric, isovaleric, 2-methylbutyric, hexanoic, octanoic and decanoic acids) in wines using the automated HS/SPME-GC-ITMS technique was developed and optimised. Five different SPME fibers were tested and the influence of different factors such as temperature and time of extraction, temperature and time of desorption, pH, strength ionic, tannins, anthocyans, SO(2), sugar and ethanol content were studied and optimised using model solutions. Some analytes showed matrix effect so a study of recoveries was performed. The proposed HS/SPME-GC-ITMS method, that covers the concentration range of the different analytes in wines, showed wide linear ranges, values of repeatability and reproducibility lower than 4.0% of RSD and detection limits between 3 and 257 μgL(-1), lower than the olfactory thresholds. The optimised method is a suitable technique for the quantitative analysis of short-chain fatty acids from the aliphatic series in real samples of white, rose and red wines.     

Development of a static headspace gas chromatographic/mass spectrometric method to analyze the level of volatile contaminants biodegradation

Volatile compound biodegradation analysis usually requires the time-consuming step of extraction of the analytes from the matrix using organic solvents or costly radioactive-compounds. Thus, it is desirable to have a simple and fast technique to generate a good evaluation of bacterial biodegradation. The goal of this research was to develop a methodology on the basis of static headspace-gas chromatography/mass spectrometry (HS-GC/MS) to evaluate the level of volatile contaminant biodegradation. The effects of the following parameters were studied: temperature and time of equilibration. The biodegradation experiments were carried out with bacteria inoculation in mineral media in presence of volatile hydrocarbon compounds (toluene, p-xylene, nonane and naphthalene). Autoclaved inoculates were used as control and reference sample. The optimal headspace conditions were observed when the vials were heated at 80 degrees C for 20 min, the syringe at 81 degrees C and an injection volume of 0.4 mL was used. This methodology has the advantage of being relative free from matrix effects.     

Elimination of matrix effects for headspace solid-phase microextraction of important volatile compounds in red wine using a novel coating

In this paper, hydroxy-terminated silicone oil-butyl methacrylate-divinylbenzene (OH-TSO-BMA-DVB) copolymer was first synthesized and used as stationary phase with the aid of γ-methacryloxypropyltrimethoxylsilane (KH-570) as bridge in solid-phase microextraction (SPME) using sol–gel method and cross-linking technique. It has high extraction efficiency for both polar alcohols and fatty acids and nonpolar esters in comparison with commercial PDMS, PDMS-DVB and PA fibers. A simple and sensitive headspace SPME-gas chromatography (HS-SPME-GC) method using the novel fiber was presented for the simultaneous analysis of both polar alcohols and fatty acids and nonpolar esters in wine. To check the matrix effects, various model wine matrices, including distilled water; 11.5% ethanol/water (v/v) solution; a concentrated synthetic wine; a ‘volatile-free’ wine and a real wine were investigated in detail. Matrix effects were compensated for by using internal standard method and selecting the ‘volatile-free’ wine as working standard. The method presented in this study showed satisfactory linearity, precision, detection limits and accuracy. The recoveries obtained ranged from 85.87 to 104.2%, and the relative standard deviation values were below 9%. The results obtained indicated that the present method is a validated and accurate procedure for the simultaneous determination of both polar and nonpolar aroma compounds in wine.     

Development of a headspace solid phase microextraction-gas chromatography method for monitoring volatile compounds in extended time-course experiments of olive oil

A novel method for monitoring fibre performance and death, based on a Shewhart control plot, for use in headspace analysis by solid phase microextraction-gas chromatography (SPME-GC) is presented. The method is also demonstrated to be effective in standardising fibre response in extended time-course experiments, where several fibres may be required to complete a lengthy study. Extraction conditions that gave good total recovery and diversity of compounds, from olive oil headspace were found to be: 1 g oil sample in 10 mL vessel; exposure of DVB-CAR-PDMS, 50/30 μm fibre for 30 min at 40 °C; and desorption for 3 min at 250 °C. Calibration curves were constructed for 25 compounds commonly reported in olive oil headspace; with coefficients of determination (R²) ranging from 0.959 to 0.994 and limits of detection (LOD) from 0.01 to 0.59 μg/g. The method was applied to monitor the change in concentration of select C6 volatile compounds, which have implications in sensory quality - E-2-hexenal, hexanal, E-2-hexen-1-ol, hexanol - over a period of 12 months storage.