HS-SPME Extraction Research Articles

Effect of puffing treatment on volatile components of green tea explored by gas chromatography–mass spectrometry and gas chromatography-olfactometry

The effect of puffing treatment on the volatile components of green tea has been studied. A total of 155 volatile compounds were identified by using HS-SPME and SPE extraction methods, combined with gas chromatography–mass spectrometry (GC–MS). The total concentration of volatile compounds in puffed green tea increased by 2.25 times compared to that in before puffing. 12 key volatile compounds in green tea were identified before and after puffing using a combination of multivariate statistical analysis, GC-O, AEDA dilution analysis, and relative odor activity value (rOAV). The puffing process generates the Maillard reaction, where sugars react with amino acids to produce Maillard reaction products (such as pyrazine, pyrrole, furan, and their derivatives), giving them a unique baking aroma. The proportion of these compounds in the total volatile matter increased. The research results provided guidance and a theoretical basis for improving the aroma processing of green tea.

Partitioning, solubility and solubilization of limonene into water or short‐chain phosphatidylcholine solutions

AbstractUsing headspace solid‐phase microextraction (HS–SPME), equilibrium distributions could be determined for hydrophobic solutes in closed systems containing vapor and aqueous solution, either in the absence or presence of two short‐chain phospholipids, dihexanoyl‐phosphatidylcholine (diC6PC) and diheptanoyl‐phosphatidylcholine (diC7PC). Without phospholipid, HS–SPME with short extraction times was used to measure water–vapor partition coefficients for d‐limonene at five temperatures within 15–40°C, with results in good agreement with existing literature. The temperature dependence of yielded the enthalpy of volatilization 34.5 kJ/mol for limonene. At 25°C, solubility values for d‐limonene, 1‐octanol, and n‐decane were obtained using similar measurements above aqueous solutions of various solute concentrations. Short‐time HS–SPME extraction of limonene in closed vials containing diC6PC or diC7PC micelles was also used to evaluate distributions of solute between vapor, aqueous dissolution, and micelles, for various surfactant concentrations at 15–40°C. Resulting vapor phase concentrations were analyzed using a mass balance and measured values, to obtain micelle–water partition coefficients and critical micelle concentrations. in diC6PC solutions (1–2 mM−1) weakly increased with temperature, but decreased significantly with increased temperature for diC7PC micelles (2–4 mM−1). Solubilization in short‐chain PC micelles has previously received little attention, and our results show that the extent of partitioning into these diacyl (i.e., two‐tailed) lipids is comparable to that for single‐tailed anionic or nonionic surfactants.

OPTIMIZATION OF SOLID-PHASE MICROEXTRACTION CONDITIONS OF MILK CHOCOLATE

In the current study, the Central Composite Design was applied to optimize HS-SPME extraction in order to detect 2,3,5,6 tetramethyl pyrazine in isomalt contaning milk chocolate. The optimal conditions for the three experimental responses influencing SPME efficiency were 10 min, 40 min and 57 °C for equilibration time, extraction time and extraction temperature, respectively. SPME fibers coated with 100 m polydimethylsiloxane coating, 65 µm polydimethylsiloxane/divinylbenzene coating, 75 µm carboxen/polydimethylsiloxane coating and 50/30 µm divinylbenzene/carboxen/polydimethylsiloxane on a StableFlex fiber were investigated. The preparation conditions of the chocolate samples were also evaluated by measuring their effects on the coating composition of the head space. The SPME fiber coated with 50/30 µm divinylbenzene/carboxen-polydimethylsiloxane provided the highest extraction efficiency, especially when the samples were extracted at 60 °C for 30 min under dry conditions. Eighty-one blends were extracted and experimentally detected most of which have been formerly stated as odor-active components.

Definitive Screening Designs and latent variable modelling for the optimization of solid phase microextraction (SPME): Case study - Quantification of volatile fatty acids in wines

In the present study, we apply the recently proposed Definitive Screening Designs (DSD) to optimize HS-SPME extraction in order to analyze volatile fatty acids (VFA) present in wine samples. This is the first attempt to apply this new class of designs to one of the most well-known and widely applied extraction techniques. The latent structure of the responses is also explored for defining the optimal extraction conditions. DSD is a new screening design with the potential to significantly reduce the number of experiments required to estimate the model parameters and to establish the optimum operation conditions. Therefore, there is an obvious interest in assessing the benefits of DSD in practice. In this work, this design framework is applied to the simultaneous optimization of seven extraction parameters (responses). Both qualitative and quantitative extraction parameters are considered, in order to test the flexibility of DSD designs: a two-level qualitative variable, the fiber coating, and six quantitative variables, namely the pre-incubation time, the extraction time and temperature, the headspace/sample volume, the effect of agitation during extraction and the influence of the ethanol content (sample dilution). Optimization of analytes' chromatographic responses was carried out both individually (response by response) and altogether, by modelling the responses in the latent variable space (i.e., explicitly considering their underlying correlation structure). In the end, a consensus analysis of all perspectives was considered in the definition of the overall optimal extraction conditions for the quantification of VFA in fortified wines. The solution found was to use a DVB/Car/PDMS fiber, 10 mL of samples in 20 mL vial, 40 min of extraction at 40 °C. The analysis also revealed that the factors incubation time, agitation and sample dilution do not play a significant role in explaining the variability of extraction parameters. Therefore, they were set to the most convenient levels. The methodology followed was thoroughly validated and the following figures of merit were obtained: good linearity (R2 > 0.999, for all compounds), high sensitivity (LOD and LOQ are close or below the values found in literature), recoveries of approximately 100% and suitable precision (repeatability and reproducibility lower than 7.21% and 8.61%, respectively). Finally, the optimized methodology was tested in practice. Several wine samples were analyzed and the odor activity value calculated to facilitate the identification of their importance as odor active compounds in different aged fortified wines. This work demonstrates the benefits of using DSD and latent variable modelling for the optimization of analytical techniques, contributing to the implementation of rigorous, systematic and more efficient optimization protocols.

Optimization, validation and application of headspace solid-phase microextraction gas chromatography for the determination of 1-nitro-2-phenylethane and methyleugenol from Aniba canelilla (H.B.K.) Mez essential oil in skin permeation samples

Aniba canelilla (H.B.K.) Mez is an aromatic plant from the Amazon region whose essential oil has 1-nitro-2-phenylethane (NP) and methyleugenol (ME) as major compounds. Despite of the scientifically proven antifungal and anti-inflammatory activities for these compounds, there is no report up to date about the topical permeation or quantification of NP and ME on skin samples. The aim of this study was the validation of an optimized bioanalytical method by solid-phase microextraction in headspace mode in gas chromatograph with flame ionization detector (HS-SPME-GC-FID) for the determination of NP and ME from the oil in different samples from permeation study, such as porcine ear skin (PES) layers (stratum corneum, epidermis and dermis) and receptor fluid (RF). For this propose polydimethylsiloxane fibers (100 μm) were used and HS-SPME extraction condition consisted of 53 °C, 21 min, and 5% w.v−1 NaCl addition. The wide range of the calibration curve (2.08–207.87 μg mL−1 for NP and 0.40–40.41 μg mL−1 for ME), the presence of matrix interferences and the intrinsic characteristics of HS-SPME required a data linearization using Log10. Thereby, data and the gained results presented homoscedasticity, normalization of residues and adequate linearity (r2 > 0.99) and accuracy for both compounds. In order to verify the applicability of the validated method, the HS-SPME-GC-FID procedure was performed to determine the amount of NP and ME permeated and retained in samples after Franz diffusion cell study from different dosages (20, 100 and 200 μL) of A. canelilla oil. Compounds permeation showed a progressive increase and penetration dependence based on the dosage applied. Furthermore, retention was in order receptor fluid >> dermis >> epidermis >> stratum corneum for both compounds, suggesting NP and ME could penetrate deep tissue, probably due to the partition coefficient, mass, size, and solubility of these compounds. In conclusion, the proposed method by HS-SPME-GC-FID to quantify 1-nitro-2-phenylethane and methyleugenol from Aniba canelilla essential oil was able to determine selectively, precisely and accurately these main compounds in skin permeation samples.

Identification of volatile compounds from polyolefin used for food packaging

Identification of volatile compounds from different virgin polyolefin FCMs was carried out by GC-MS with both HS-SPME and ultrasonic extraction (UE), with the aim to obtein the most amount of volatile compounds from polyolefin. Seventy compounds were identified with 90% reliability by GC-MS with NIST 14 library, most of them are NIAS.
 
 
 
 
 
 
 
 
 

HS-SPME optimization and extraction of volatile compounds from soursop (Annona muricata L.) pulp with emphasis on their characteristic impact compounds

Aroma and taste are decisive factors in the selection of any food. The aim of this study was to extract the volatile compounds present in soursop (Annona muricata L.) pulp by Solid-phase microextraction (SPME) technique using 3 different fibers (DVB/CAR/ PDMS, CAR/PDMS and PDMS/DVB). An experimental design was set up to evaluate the best extraction conditions wherein the variables were adsorption temperature, ionic strength and pulp concentration. The separation of volatiles was performed in chromatographic columns of different polarity (polar and non-polar) while volatile compounds were identified by analysis in high resolution gas chromatography system coupled with mass spectrometry. The results obtained using 3 different fibers revealed the capture of about 40 compounds. The CAR/PDMS fiber was more efficient for the capture of esters and DVB/CAR/PDMS fiber for terpenes. The optimum conditions for capture of higher number of volatiles for polar column were 45 °C for extraction, 15% of ionic strength and 50% of pulp concentration which resulted in separation of 87 compounds. Among the principal character impact compounds from soursop are (E)-2-hexenoate, methyl hexenoate and linalool.

Vacuum-assisted headspace solid phase microextraction of polycyclic aromatic hydrocarbons in solid samples

For the first time, Vacuum Assisted Headspace Solid Phase Microextraction (Vac-HSSPME) is used for the recovery of polycyclic aromatic hydrocarbons (PAHs) from solid matrices. The procedure was investigated both theoretically and experimentally. According to the theory, reducing the total pressure increases the vapor flux of chemicals at the soil surface, and hence improves HSSPME extraction kinetics. Vac-HSSPME sampling could be further enhanced by adding water as a modifier and creating a slurry mixture. For these soil-water mixtures, reduced pressure conditions may increase the volatilization rates of compounds with a low KH present in the aqueous phase of the slurry mixture and result in a faster HSSPME extraction process. Nevertheless, analyte desorption from soil to water may become a rate-limiting step when significant depletion of the aqueous analyte concentration takes place during Vac-HSSPME. Sand samples spiked with PAHs were used as simple solid matrices and the effect of different experimental parameters was investigated (extraction temperature, modifiers and extraction time). Vac-HSSPME sampling of dry spiked sand samples provided the first experimental evidence of the positive combined effect of reduced pressure and temperature on HSSPME. Although adding 2 mL of water as a modifier improved Vac-HSSPME, humidity decreased the amount of naphthalene extracted at equilibrium as well as impaired extraction of all analytes at elevated sampling temperatures. Within short HSSPME sampling times and under mild sampling temperatures, Vac-HSSPME yielded linear calibration curves in the range of 1–400 ng g−1 and, with the exception of fluorene, regression coefficients were found higher than 0.99. The limits of detection for spiked sand samples ranged from 0.003 to 0.233 ng g−1 and repeatability from 4.3 to 10 %. Finally, the amount of PAHs extracted from spiked soil samples was smaller compared to spiked sand samples, confirming that soil could bind target analytes more strongly and thus decrease the readily available fraction of target analytes.

Screening of volatile compounds composition of white truffle during storage by GCxGC-(FID/MS) and gas sensor array analyses

White truffle (Tuber magnatum Pico) is one of the most valuable delicacies of the Italian and French cuisine. Previous works on truffle aroma report sulfur compounds and short-chain aldehydes as typical constituents which abundance is influenced by storage conditions. In this study, the head space of truffle aroma has been evaluated by two different (innovative) approaches: HS-SPME extraction and comprehensive two-dimensional gas chromatography (GCxGC), exploiting a dual-stage loop-type modulator within a GC system with simultaneous FID and MS double detection, analysis and Gas sensors array system analysis. Gas chromatographic peak identification was carried out by means of dedicated laboratory-made GC–MS libraries and comparison of Retention Indices with those retrieved from literature, while peak quantification by means of a specifically designed software for comprehensive GC. The truffle samples were stored at +8 °C for four days in three different ways: wrapped in blotting paper or covered by rice or under vacuum. Eighty compounds were identified with high confidence (>90% of mass spectra similarity). PCA of compounds relative percentages showed differences among the fresh product and truffles stored in rice and under vacuum; on the contrary no significant volatiles composition modification was observed for truffles stored in paper.

Assessment of dispersive liquid–liquid microextraction conditions for gas chromatography time-of-flight mass spectrometry identification of organic compounds in honey

The suitability of the dispersive liquid–liquid microextraction (DLLME) technique for gas chromatography (GC) characterization of minor organic compounds in honey samples is evaluated. Under optimized conditions, samples were pre-treated by liquid–liquid extraction with acetonitrile followed by DLLME using carbon tetrachloride (CCl4, 0.075mL) as extractant. The yielded settled phase was analyzed by GC using high resolution time-of-flight (TOF) mass spectrometry (MS). The whole sample preparation process is completed in approximately 10min, with a total consumption of organic solvents below 4mL, relative standard deviations lower than 12% and with more than 70 organic compounds, displaying linear retention index in the range from 990 to 2900, identified in the obtained extracts. In comparison with HS SPME extraction, higher peak intensities were attained for most volatile and semi-volatile compounds amenable to both extraction techniques. Furthermore, other species such as highly polar and water soluble benzene acids, long chain fatty acids, esters and flavonoids, which are difficult to concentrate by HS SPME, could be identified in DLLME extracts. Some of the compounds identified in DLLME extracts have been proposed as useful for samples classification and/or they are recognized as markers of honeys from certain geographic areas.

Multiple headspace solid-phase microextraction for quantifying volatile free fatty acids in cheeses

Multiple headspace solid-phase microextraction (MHS-SPME) has been utilized for the quantitative determination of 9 volatile free fatty acids (FFAs) in cheeses, in combination with gas-chromatography and flame-ionization detection (GC-FID). Variables affecting HS-SPME and MHS-SPME were optimized to attain adequate sensitivity while allowing correct application of the MHS method. Thus, the MHS-SPME method was successfully performed when using 0.3g of cheese and 1mL of NaCl (sat. solution), which is subjected to four consecutive extractions using the carboxen–polydimethylsyloxane (CAR–PDMS) as the commercial SPME coating, 40min of HS extraction time at 45°C, and 6min of desorption time in the GC injector at 290°C. The MHS-SPME permitted the calculation of β values, which range from 0.72±0.01–0.95±0.02, depending on the cheese studied. Later, this β parameter is used to perform quantitation for the 9 volatile FFAs after just a single HS-SPME extraction, using an external solvent calibration curve. The validity of the utilization of an external solvent calibration was tested with aqueous standards of volatile FFAs, getting average recoveries higher than 81.2%. Quantitation by MHS-SPME was free of matrix interferences despite measuring a complex cheese sample. The optimized method was validated, presenting inter-day reproducibility values (as RSD in %) lower than 13%, and limits of detection down to 7µgkg−1. The method was also compared with a conventional extraction method such as solid-phase extraction for the studied cheeses elaborated with goat milk, generating comparable results. To our knowledge, this is the first time that MHS-SPME has been applied to volatiles in cheeses.

Phytochemical and physical–chemical analysis of Polish willow (Salix spp.) honey: Identification of the marker compounds

The case study of Polish Salix spp. honey was compared with published data on willow honey from other regions. GC-FID/MS (after HS-SPME and ultrasonic solvent extraction) and targeted HPLC-DAD were applied. Phenolic content, FRAP/DPPH assays and the colour coordinates were determined spectrophotometrically. Beside ubiquitous linalool derivatives, borneol (up to 10.9%), bicyclic monoterpenes with pinane skeleton (pinocarvone up to 10.6%, myrtenal up to 4.8% and verbenone up to 3.4%) and trans-β-damascenone (up to 13.0%) dominated in the headspace. The main compounds of the extractives were vomifoliol (up to 39.6%) and methyl syringate (up to 16.5%) along with not common 4-hydroxy-3-(1-methylethyl)benzaldehyde (up to 11.1%). Abscisic acid (ABA) was found (up to 53.7mg/kg) with the isomeric ratio (Z,E)-ABA:(E,E)-ABA=1:2. The honey exhibited low antioxidant potential with pale yellow colour. The composition of Polish willow honey is similar to Mediterranean willow honeys with several relevant differences.

Development of Microwave‐Assisted Extraction Procedure for Organic Impurity Profiling of Seized 3,4‐Methylenedioxymethamphetamine (MDMA)*,†

Organic impurity profiling of seized 3,4-methylenedioxymethamphetamine (MDMA) tablets aims to link tablets to common production sources. Conventionally, organic impurities are extracted from tablets using a liquid-liquid extraction (LLE) procedure prior to analysis by gas chromatography-mass spectrometry (GC-MS). In this research, the development of an alternative microwave-assisted extraction/headspace solid-phase microextraction (MAE/HS-SPME) procedure is described. The optimal procedure used phosphate buffer (1 M, pH 8), with an HS-SPME extraction temperature of 70 °C for 40 min, using a divinylbenzene/Carboxen™/polydimethylsiloxane (DVB/CAR/PDMS) fiber. Impurities were extracted from seized MDMA exhibits using the MAE/HS-SPME procedure, as well as HS-SPME alone, and a conventional LLE procedure. The HS-SPME procedure was deemed to be the most practical because of the affordability and need for less analyst involvement. Although the LLE was limited in the number of impurities extracted, the procedure is still useful for the extraction of less volatile impurities that are not extracted by HS-SPME.

Qualitative and quantitative analysis of volatile components of Teucrium massiliense L. – identification of 6‐methyl‐3‐heptyl acetate as a new natural product

AbstractVolatile components extracted from the aerial parts and separated organs of Corsican and Sardinian Teucrium massiliense have been studied. The chemical composition of essential oils obtained by hydrodistillation (HD) has been investigated using GC–RI, GC–MS (EI and CI modes) and 13CNMR spectroscopy. For the first time, a real concentration via calibration curves and response factor calculations has been determined for each oil component. The concentrations of the major components were 6‐methyl‐3‐heptyl acetate (23.83–18.16 g/100 g), 3‐octyl acetate (10.55–6.95 g/100 g), isobutyl isovalerate (7.67–2.91 g/100 g), germacrene D (6.13–1.01 g/100 g) and linalool (6.63–5.23 g/100 g). To the best of our knowledge, the occurrence of 6‐methyl‐3‐heptyl acetate as a natural product is reported for the first time. Furthermore, the chemical composition of volatile fractions emitted from the aerial parts and separated organs of T. massiliense L. has been studied by HS–SPME/GC–RI and GC–MS after optimization of SPME parameters. Concerning the contribution of plant organs to the aromatic plant fingerprint, we noted that the flowers produced more volatiles than other organs. The volatile fractions obtained from the different organs were qualitatively quite similar to each other but differed in the percentages of their major components. Also, the influence of HS–SPME extraction parameters (equilibrium and extraction times and temperature) on the chemical composition of the plant volatile fraction is discussed. Copyright © 2010 John Wiley & Sons, Ltd.

HS-SPME/GCxGC/TOF-MS: A Powerful Tool for Off-flavors Identification in Italian Muscat-based Wines

Muscat Blanc a Petits Grains grape (Vitis vinifera L.) is used for the production of Asti (or Asti Spumante) and Moscato d'Asti wines from Piedmont (Italian DOCG designation, D.M. 29-11-1993). The sweet floral aroma from Muscat grapes is a required sensorial quality of these wines. The evolution of the volatile aroma in wine is correlated to many parameters (grape variety, winemaking practices, microbial starters and microflora development, ageing). The oxidation of some compounds was reported to be of fundamental importance in Muscat-type wines aroma (ARLORIO et al. 2005). The unexpected development of off-flavors is a common accident, also in white sparkling wines (LIZARRAGA et al. 2004). The aim of our work was to develop a high-sensitive multi-dimensional comprehensive capillary gas chromatographic method for the analysis of Muscat wines volatile compounds. Second aim was the application of this method to the study of the evolution of the volatile aroma (via Head-Space Solid Phase Micro Extraction, HS-SPME) during the ageing of Asti Spumante and Moscato d'Asti DOCG. wines. A divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS) fibre was used in HS-SPME extraction from all wine samples. The volatile aroma was analysed using GC×GC coupled with a Time of Flight Mass Detector (TOF-MS) (RIBEREAU-GAYON et al. 1975). Qualitative complex - multidimensional profiles were obtained; terpenoids were easily identified in Muscat wines, employing both commercial standards and NIST mass spectral library. In one-year aged wine samples, linalool, nerol and geraniol decreased respect to the young Muscat wine to become less important regarding the aroma, as previously described by other authors. Therefore, α-terpineol, hotrienol, nerol oxide, furanic linalool oxides A/B and rose oxide concentration significantly increased, confirming an oxidative evolution of the aroma. We also identify some off-flavors, responsible of wine imperfections described as cork tones, plastic, mushroom. The presences of 2,4,6-trichloroanisole and 2,4,6-tribromoanisole have been highlighted in some samples. Many other "in trace" compounds (still unidentified) were present in all multidimensional chromatograms.) Finally, HS-SPME/GC×GC/TOF-MS chromatographic analysis of Muscat-based wine volatiles, proved to be a novel powerful technique for the description of qualitative-quantitative complex fingerprints during the aroma evolution, establishing bases for further investigation in the "volatile fraction" of aroma of these aromatic wines.

Development and application of a simplified sample preparation method for determination of TEGDMA and related metabolites

Analysis of biological samples obtained from in vivo experiments can be often challenging. In general it is not possible to apply the commonly used matrices that are necessary for the experiments to the desired analysis systems without further conditioning or sample purification steps. Besides possible adverse effects for instruments, interference between analytes and matrices can affect the correct measurement of analytes. Different methods of sample preparation can be used to convert biological samples into samples suitable for analysis; SPE and HS-SPME are two well established methods. Research of in vivo metabolism of triethyleneglycoledimethacrylate (TEGDMA), one of the most frequently contained comonomer in dental restorative materials, demands sample preparation methods that offer separation of TEGDMA and its related metabolites from biological matrices. In the presented study two methods for sample preparation were developed in order to analyze TEGDMA as well as its metabolites triethyleneglycole (TEG), 2,3-epoxymethacrylicacid methylester (2,3-EMME), and methacrylacid methylester (MAME) in Krebs-Henseleit buffer samples to facilitate a subsequent analysis via GC-MS. An easy and time-saving separation protocol was developed. Recovery rates of TEGDMA and TEG after SPE were 21 +/- 3% and 105 +/- 12%, respectively, recovery rate after headspace extraction of 2,3-EMME and MAME was higher at 48 degrees C compared with 20 degrees C extraction temperature. The tested range for 2,3-EMME and MAME concentration after HS-SPME extraction was 0.1-100 mg/L and both analytes showed a good linearity.

Volatile Constituents of Achillea ligustica All. by HS-SPME/GC/GC-MS. Comparison with Essential Oils Obtained by Hydrodistillation from Corsica and Sardinia

The volatile components extracted from the headspace (HS) of Achillea ligustica All. samples and their separated organs using solid phase microextraction (SPME) were investigated by gas chromatography (GC) and gas chromatography-mass spectrometry (GC/MS). Fifty seven compounds were identified, the main components were camphor (14.2 - 29.8 %), artemisia ketone (0.3 - 26.7 %), santolina alcohol (0.5 - 9.4 %), camphene (3.0 - 9.0 %) and trans-sabinyl acetate (1.6 - 5.5 %). Moreover, the chemical composition of Corsican and Sardinian A. ligustica oils obtained from flowers and leafy stems harvested in four regions of both islands, were investigated. Two collective oils of A. ligustica were also investigated, comparisons between both oils and as well as with literature data were reported. A comparison of hydrodistillation and HS-SPME extraction of volatile components in term of isolation time, plant-consuming and chemical composition was discussed. HS-SPME technique was clearly fast in contrast to hydrodistillation (90 mn/300 mn). HS extraction was performed with very smaller amount of plant than hydrodistillation. Although the aromatic profiles of HS-fractions and oils showed several quantitative differences HS-SPME can be applied to routine control analysis of aromatic and medicinal plants.

Application of multiple headspace-solid-phase microextraction followed by gas chromatography–mass spectrometry to quantitative analysis of tomato aroma components

The objective of this paper is to investigate the potential of multiple headspace-solid-phase microextraction (MHS-SPME) for the determination of volatile compounds in complex matrix samples. A method based on MHS-SPME for the determination of around 20 volatile compounds, responsible of tomato flavour and aroma has been developed and validated, using gas chromatography with mass spectrometry (ion trap analyser) for analysis. For this purpose, the experimental β parameter, resulting from the MHS-SPME theoretical development, has been obtained from real sample analysis (in triplicate) for each identified compound, carrying out up to 5 consecutive extractions. Later, this parameter is used to perform quantitation of real samples after just a single HS-SPME extraction. Precision, expressed as repeatability, has been evaluated by analysing six replicates of a real sample, showing relative standard deviations between 4 and 20%. For accuracy study, quantitative results have been compared with those obtained by means of standard additions on replicate samples, and no statistically significant differences between the two methods were observed. Since MHS-SPME uses the estimated total area corresponding to the complete extraction of compounds (obtained from the β parameter), quantitation can be carried out by external calibration using standards in solvent and splitless injection, instead of by SPME. Linearity, tested in the range 0.05–15 μg/mL, showed satisfactory values, with coefficients of correlation between 0.995 and 0.999. Limits of detection were in the range of 0.25–5 ng/g. MHS-SPME has been proved to be an adequate technique to avoid matrix effects in complex samples quantitation. Its applicability to the determination of volatile tomato components, together with its limitations, is discussed in this article.

Optimisation of a complete method for the analysis of volatiles involved in the flavour stability of beer by solid-phase microextraction in combination with gas chromatography and mass spectrometry

Headspace solid-phase microextraction combined with gas chromatography and mass spectrometry was used for the quantification of 32 volatiles which represent the typical chemical reactions that can occur during beer ageing. Detection was accomplished by employing on-fibre derivatisation using o-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (PFBHA) and normal HS-SPME extraction. The procedures were optimised for SPME fibre selection, PFBHA loading temperature and time, extraction temperature and time, and effect of salt addition. Interference of matrix effects was overcome by calibrating according to the standard addition method and by using internal standards. Afterwards, the method was validated successfully and was applied to study the flavour stability of different beer types.