Headspace Solid-phase Microextraction Technique Research Articles

New cloud vapor zone (CVZ) coupled headspace solid-phase microextraction technique

A new cloud vapor zone (CVZ)-based headspace solid-phase microextraction (HS-SPME) technique has been demonstrated with the capability of heating the sample matrix and simultaneously cooling the sampling zone. A bi-temperature-controlled (BTC) system, allowing 10 mL of test sample heating and headspace external-cooling, was employed for the CVZ formation around the SPME-fiber sampling area. In the CVZ procedure, the heated headspace vapor undergoes a sudden cooling near the SPME to form a dense cloud of analyte-water vapor, which is helpful for adsorption or absorption of the analyte. The device was evaluated for the quantitative analysis of aqueous chlorothalonil. Parameters influencing sampling efficiency, e.g., SPME fiber coating, SPME sampling temperature and time, solution modifier, addition of salt, sample pH, and temperature, were investigated and optimized thoroughly. The proposed BTC-HS-SPME method afforded a best extraction efficiency of above 94% accuracy (less than 4.1% RSD, n=7) by using the PDMS fiber to collect chlorothalonil in the headspace at 5 degrees C under the optimized condition, i.e., heating sample solution (added as 10% ethylene glycol and 30% NaCl, at pH 7.0) at 130 degrees C for 15 min. The detection was linear from 0.01 to 80 microg L-1 with a regression coefficient of 0.9998 and had a detection limit of 3.0 ng L-1 based on S/N=3. Practical application was demonstrated by analyzing chlorothalonil in farm water samples with promising results and recoveries. The approach provided a very simple, fast, sensitive, and solvent-free procedure to collect analytes from aqueous solution. The approach can provide a new platform for other sensitive HS-SPME assays.

Improved method for the in vitro assessment of antioxidant activity of plant extracts by headspace solid-phase microextraction and gas chromatography–electron capture detection

The simultaneous monitoring of malondialdehyde, pentanal and hexanal, final products of lipid peroxidation is reported, using a headspace solid-phase microextraction (HS-SPME) technique with on-fibre derivatisation. The aldehydes are extracted and subjected to on-sorbent derivatisation into stable hydrazones with 2,4,6-trichlorophenylhydrazine (TCPH) and analyzed. The degree of inhibition of oxidation is performed by monitoring the chlorinated hydrazones after thermal desorption, by gas chromatography–electron capture detection. The procedure was employed to evaluate in vitro the antioxidant activity of Hypericum perforatum L. extracts and of the well-known antioxidant vitamin E following induction of oxidation of sunflower oil, as a model lipid system. Prior to the measurement of antioxidant activity, the optimal process conditions, i.e. headspace volume, temperature, agitation, extraction/derivatisation time and desorption time and temperature were properly established. Aqueous extracts of H. perforatum L. exhibited the highest antioxidative effect. The method is shown to be promising for screening purposes for antioxidant substances and natural extracts.

Headspace solid‐phase microextraction of cannabinoids in human head hair samples

A fast method was optimized and validated with the aim to detect cannabinoids (cannabidiol, cannabinol, and delta-9-tetrahydrocannabinol) in human head hair samples. The method was based on an initial procedure of external decontamination of hair samples (10 mg) with petroleum ether, followed by alkaline digestion and further extraction of cannabinoids by means of a headspace solid-phase microextraction technique (HS-SPME). GC-MS was used to identify and quantify the analytes in SIM mode. The LOQs and LODs obtained were 0.07 and 0.12 ng/mg, respectively, for all the studied cannabinoids. The method proved to be simple, rapid, and precise. By using the weighted least squares linear regression (weighting factor 1/x2), the accuracy of the analytical method was improved at the lower end of the calibration curve (from 0.12 to 12 ng/mg; r >0.98). Hair samples collected from eight volunteers (in-patients of a drug abuse rehabilitation clinic) were submitted to the proposed method. Detection of the drugs was observed in samples of the volunteers who reported frequent marijuana use (at least ten times a week).

Solid-phase microextraction for headspace analysis of key volatile compounds in orange beverage emulsion

Headspace solid-phase microextraction (HS-SPME) gas chromatography was used to analyze target flavor compounds in orange beverage emulsion. The effects of SPME fiber (PDMS 100 μm, CAR/PDMS 75 μm, PDMS/DVB 65 μm and DVB/CAR/PDMS 50/30 μm), adsorption temperature (25–45 °C), adsorption time (5–25 min), sample concentration (1–100%), sample amount (5–12.5 g), pH (2.5–9.5), salt type (K 2CO 3, Na 2CO 3, NaCl and Na 2SO 4), salt amounts (0–30%) and stirring mode were studied to develop HS-SPME condition for obtaining the highest extraction efficiency and aroma recovery. For the head space volatile extraction, the optimum conditions were: CAR/PDMS fiber, adsorption at 45 °C for 15 min, 5 g of diluted beverage emulsion (1:100), 15% (w/w) of NaCl with stirring and original pH 4. The main volatile flavor compounds were: limonene, 94.9%; myrcene, 1.2%; ethyl butyrate, 1.1%; γ-terpinene, 0.41%; linalool, 0.36%; 3-carene, 0.16%; decanal, 0.12%; ethyl acetate, 0.1%; 1-octanol, 0.06%; geranial, 0.05%; β-pinene, 0.04%; octanal, 0.03%; α-pinene, 0.03%; and neral, 0.03%. The linearity was very good in the considered concentration ranges ( R 2 ⩾ 0.97). Average recoveries ranged from 88.3% to 121.7% and showed good accuracy for the proposed analytical method. Average relative standard deviation (RSD) for five replicate analyses was found to be less than 14%. The limit of detection (LOD) ranged from 0.06 to 2.27 mg/l for all volatile flavor compounds and confirmed the feasibility of the HS-SPME technique for headspace analysis of orange beverage emulsion. The method was successfully applied for headspace analysis of five commercial orange beverage emulsions.

Changes in Headspace Volatile Concentrations of Coffee Brews Caused by the Roasting Process and the Brewing Procedure

Headspace-solid-phase microextraction technique (HS-SPME) coupled with gas chromatography-mass spectrometry (GC-MS) and gas chromatography-olfactometry (GC-O) were used to characterize the aroma compounds of coffee brews from commercial conventional and torrefacto roasted coffee prepared by filter coffeemaker and espresso machine. A total of 47 volatile compounds were identified and quantified. Principal component analysis (PCA) was applied to differentiate coffee brew samples by volatile compounds. Conventional and torrefacto roasted coffee brews were separated successfully by principal component 1 (68.5% of variance), and filter and espresso ones were separated by principal component 2 (19.5% of variance). By GC olfactometry, a total of 34 aroma compounds have been perceived at least in half of the coffee extracts and among them 28 were identified, among which octanal was identified for the first time as a contributor to coffee brew aroma.

Simultaneous determination of selegiline and desmethylselegiline in human body fluids by headspace solid-phase microextraction and gas chromatography–mass spectrometry

A method for the simultaneous determination of selegiline and its metabolite, desmethylselegiline, in human whole blood and urine is presented. The method, which combines a fiber-based headspace solid-phase microextraction (SPME) technique with gas chromatography–mass spectrometry (GC–MS), required optimization of various parameters (e.g., salt additives, extraction temperatures, extraction times and the extraction properties of the SPME fiber coatings). Pargyline was used as the internal standard. Extraction efficiencies for both selegiline and desmethylselegiline were 2.0–3.4% for whole blood, and 8.0–13.2% for urine. The regression equations for selegiline and desmethylselegiline extracted from whole blood were linear ( r 2 = 0.996 and 0.995) within the concentration ranges 0.1–10 and 0.2–20 ng/ml, respectively. For urine, the regression equations for selegiline and desmethylselegiline were linear ( r 2 = 0.999 and 0.998) within the concentration ranges 0.05–5.0 and 0.1–10 ng/ml, respectively. The limit of detection for selegiline and desmethylselegiline was 0.01–0.05 ng/ml for both samples. The lower and upper limits of quantification for each compound were 0.05–0.2 and 5–20 ng/ml, respectively. Intra- and inter-day coefficients of variation for selegiline and desmethylselegiline in both samples were not greater than 8.7 and 11.7%, respectively. The determination of selegiline and desmethylselegiline concentrations in Parkinson's disease patients undergoing continuous selegiline treatment is presented and is shown to validate the present methodology.

Headspace solid-phase microextraction applied to the simultaneous determination of sorbic and benzoic acids in beverages

A new analytical procedure was developed using headspace solid-phase microextraction (HS-SPME) for the simultaneous determination of sorbic and benzoic acids in beverages. The sample were processed depending on their nature, either only diluted with water, or treated with a NaOH solution and filtered through a 0.45-μm membrane filter. The samples were heated in a vial in the presence of sulfuric acid and anhydrous sodium sulfate and the analytes were collected from the headspace by using a 65-μm polydimethylsiloxane–divinylbenzene (PDMS–DVB) coated fiber and determined by gas chromatography with flame ionization detector (GC-FID). To enhance the sensitivity of HS-SPME, the temperature and time of the extraction and desorption, the acidity and salt concentration of the extraction solution were optimized. Linear range of the analytes was found to be between 0.1 and 20 mg/L with regression coefficients ( R 2) of 0.9998 for sorbic acid and 0.9980 for benzoic acid. Limits of detection (LOD) were 5.83 μg/L and 11.4 μg/L for sorbic and benzoic acids, respectively. Relative standard deviation (R.S.D.) for six replicate analyses within 3 days (two times/day) was found to be lower than 8.62% at three concentration levels (2, 6, 10 mg/L). Recoveries ranged from 81.20% to 108.1% for real samples. The results demonstrate the suitability of the HS-SPME technique to analyze sorbic and benzoic acids in a variety of beverages.

Quantitative Determination of Thermally Derived Off-Flavor Compounds in Milk Using Solid-Phase Microextraction and Gas Chromatography

Many volatile compounds generated during the thermal processing of milk have been associated with cooked, stale, and sulfurous notes in milk and are considered as off-flavor by most consumers. A headspace solid-phase microextraction (HS-SPME)/gas chromatographic technique for the quantitative analysis of thermally derived off-flavor compounds was developed in this study. The extraction temperature, time, and sample amount were optimized using a randomized 23 central composite rotatable design with 2 central replicates and 2 replicates in each factorial point along with response surface methodology. Calibration curves were constructed in milk using the standard addition technique, and then used to quantify 20 off-flavor compounds in raw, pasteurized, and UHT milk samples with various fat contents. The concentrations of these volatiles in raw and pasteurized milk samples were not significantly different. However, dimethyl sulfide, 2-hexanone, 2-heptanone, 2-nonanone, 2-undecanone, 2-methylpropanal, 3-methylbutanal, heptanal, and decanal were found at higher concentrations in UHT milk as compared with raw and pasteurized milk samples. In addition, the concentration of methyl ketones was greater in UHT milk with higher fat content. The calculated odor activity values suggested that 2,3-butanedione, 2-heptanone, 2-nonanone, 2-methylpropanal, 3-methylbutanal, nonanal, decanal, and dimethyl sulfide could be important contributors to the off-flavor of UHT milk. The HS-SPME technique developed in this study is accurate and relatively simple, and can be used for the quantification of thermally derived off-flavor compounds in milk.

Determination of halogenated solvents content in olive oil by two completely automated headspace techniques coupled to gas chromatography–mass spectrometry

Two different methods have been developed and compared for determining the halogenated solvents content of olive oils. The optimal parameters for isolation and preconcentration of relevant halogenated solvents (bromodichloromethane, dibromochloromethane, chloroform, bromoform, tetrachloroethene, trichloroethene, ethylenedichloride, and vinyl chloride) were established. These proposed procedures are completely automated and do not require reagents because both methods are based on headspace techniques, conventional headspace (HS) and headspace solid-phase microextraction (HS-SPME), both techniques on-line coupled to a gas chromatograph–mass spectrometer (GC–MS) operated in selected ion monitoring (SIM) mode. The methods were validated and compared their figures of merit. In general, both extraction techniques presented similar extraction efficiency at the studied concentrations. However, average relative standard deviation (R.S.D.) obtained at low concentration levels was slightly better for HS (8.6%) than for HS-SPME (11.8%) technique. It was due to the lower limits of detection (LOD) and quantification (LOQ) values obtained for HS, especially for the less volatile vinyl chloride, chloroform and ethylene dichloride compounds. Finally, the HS-GC–MS method was applied to the analysis of real olive oil and olive-pomace oil samples. None content of halogenated solvents was found above the LOD in the studied samples. The proposed methods are faster, simpler and easier than the official methods proposed by the European Union and the International Olive Oil Council.

Multivariate analysis for the classification and differentiation of Madeira wines according to main grape varieties

In order to differentiate and characterize Madeira wines according to main grape varieties, the volatile composition ( higher alcohols, fatty acids, ethyl esters and carbonyl compounds) was determined for 36 monovarietal Madeira wine samples elaborated from Boal, Malvazia, Sercial and Verdelho white grape varieties. The study was carried out by headspace solid-phase microextraction technique (HS-SPME), in dynamic mode, coupled with gas chromatography–mass spectrometry (GC–MS). Corrected peak area data for 42 analytes from the above mentioned chemical groups was used for statistical purposes. Principal component analysis (PCA) was applied in order to determine the main sources of variability present in the data sets and to establish the relation between samples (objects) and volatile compounds (variables). The data obtained by GC–MS shows that the most important contributions to the differentiation of Boal wines are benzyl alcohol and ( E)-hex-3-en-1-ol. Ethyl octadecanoate, ( Z)-hex-3-en-1-ol and benzoic acid are the major contributions in Malvazia wines and 2-methylpropan-1-ol is associated to Sercial wines. Verdelho wines are most correlated with 5-(ethoxymethyl)-furfural, nonanone and cis-9-ethyldecenoate. A 96.4% of prediction ability was obtained by the application of stepwise linear discriminant analysis (SLDA) using the 19 variables that maximise the variance of the initial data set.

Determination of clenbuterol in urine using headspace solid phase microextraction or liquid–liquid–liquid microextraction

Headspace solid phase microextraction (HS-SPME) and liquid–liquid–liquid microextraction with automated movement of the acceptor phase (LLLME/AMAP) techniques are described for the extraction of clenbuterol (CB) in urine. HS-SPME technique involves the extraction of the drug by SPME fibre in a headspace mode with a cooling device at the upper part of the vial to cool the headspace of the vial where the fiber is suspended. This cooling effect will enhance the absorption of analytes by the fiber. As the cooling system is surrounding the vial, the headspace will also be cooled in addition to the cooling of the fiber. After extraction the derivatization of the extracted drug with hexamethyldisilazane (HMDS) was performed by suspending the fiber in the headspace of another vial saturated with the vapor of HMDS. This derivatized compound was analyzed by gas chromatography with mass spectrometric detection (GC/MS). LLLME/AMAP technique involves the extraction of CB, a basic drug, from an alkaline solution into the organic solvent residing in the pores of the hollow fiber and then back extracted into the acidic acceptor solution inside the lumen of the hollow fiber. The acceptor solution was repeatedly moved in and out of the hollow fibre assisted by a syringe pump. This repeated movement provides fresh acceptor phase to come in-contact with the organic phase and thus improving the efficiency of extraction. Quantification was performed using high performance liquid chromatography with ultraviolet (HPLC/UV) detection. In both the techniques, experimental parameters have been studied to achieve greater sensitivity. Linearity was observed over the range of 1–1000 ng ml −1 ( R 2 = 0.9990) and 50–3000 ng ml −1 ( R 2 = 0.9956) with detection limits of 0.23 ng ml −1 and 3.9 ng ml −1, respectively, for HS-SPME-GC/MS and LLLME/AMAP-HPLC/UV method. R.S.D. values of 3.9% (HS-SPME-GC/MS) and 5.8% (LLLME/AMAP-HPLC/UV) indicated good precision of the techniques. Absolute recovery was found to be 0.007% and 18%, respectively, for HS-SPME-GC/MS and LLLME-HPLC/UV methods. Finally, the techniques have been applied for the analysis of CB in urine samples. No effort has been made to compare the method with official method.

Sensitive quantification of sulfur compounds in wine by headspace solid-phase microextraction technique

A sensitive solid-phase microextraction and gas chromatography-pulsed flame photometric detection technique was developed to quantify volatile sulfur compounds in wine. Eleven sulfur compounds, including hydrogen sulfide, methanethiol, ethanethiol, dimethyl sulfide, diethyl sulfide, methyl thioacetate, dimethyl disulfide, ethyl thioacetate, diethyl disulfide, dimethyl trisulfide and methionol, can be quantified simultaneously by employing three internal standards. Calibration curves were established in a synthetic wine, and linear correlation coefficients ( R 2) were greater than 0.99 for all target compounds. The quantification limits for most volatile sulfur compounds were 0.5 ppb or lower, except for methionol which had a detection limit of 60 ppb. The recovery was studied in synthetic wine as well as Pinot noir, Cabernet Sauvignon, Pinot Grigio, and Chardonnay wines. Although the sulfur compounds behaved differently depending on the wine matrix, recoveries of greater than 80% were achieved for all sulfur compounds. This technique was applied to analyze volatile sulfur compounds in several commercial wine samples; methionol concentrations were found at the ppm level, while the concentrations for hydrogen sulfide, methanethiol, and methyl thioacetate were at ppb levels. Only trace amounts of disulfides and trisulfides were detected, and ethanethiol was not detected.

Interactions between Volatile and Nonvolatile Coffee Components. 1. Screening of Nonvolatile Components

This study is the first of two publications that investigate the phenomena of coffee nonvolatiles interacting with coffee volatile compounds. The purpose was to identify which coffee nonvolatile(s) are responsible for the interactions observed between nonvolatile coffee brew constituents and thiols, sulfides, pyrroles, and diketones. The overall interaction of these compounds with coffee brews prepared with green coffee beans roasted at three different roasting levels (light, medium, and dark), purified nonvolatiles, and medium roasted coffee brew fractions (1% solids after 1 or 24 h) was measured using a headspace solid-phase microextraction technique. The dark roasted coffee brew was slightly more reactive toward the selected compounds than the light roasted coffee brew. Selected pure coffee constituents, such as caffeine, trigonelline, arabinogalactans, chlorogenic acid, and caffeic acid, showed few interactions with the coffee volatiles. Upon fractionation of medium roasted coffee brew by solid-phase extraction, dialysis, size exclusion chromatography, or anion exchange chromatography, characterization of each fraction, evaluation of the interactions with the aromas, and correlation between the chemical composition of the fractions and the magnitude of the interactions, the following general conclusions were drawn. (1) Low molecular weight and positively charged melanoidins present significant interactions. (2) Strong correlations were shown between the melanoidin and protein/peptide content, on one hand, and the extent of interactions, on the other hand (R = 0.83-0.98, depending on the volatile compound). (3) Chlorogenic acids and carbohydrates play a secondary role, because only weak correlations with the interactions were found in complex matrixes.

Development of a headspace solid-phase microextraction method combined with gas chromatography mass spectrometry for the determination of phthalate esters in cow milk

Phthalate esters released from plasticized polyvinyl chloride (PVC) tubing into raw cow milk during milking at dairy farms could be a potential source of contamination by phthalate esters in dairy products. A method was developed for the determination of these phthalate esters in raw cow milk samples using a headspace solid-phase microextraction (HS-SPME) technique. The milk samples were mixed with sodium chloride and extracted for 60 min at 90 °C. The phthalates collected on the SPME fibre were then desorbed in the GC injection port followed by GC-MS analysis in single ion monitoring (SIM) mode. The extraction efficiency of the SPME fibre was dependent on the fat content in the milk sample. Since the fat content in each cow milk sample was different, a combined standard addition and internal standard method was used for the quantification of the phthalate esters in milk samples. The recoveries at two spiking levels were over 90% except for dimethyl phthalate. The method detection limit for di-(2-ethylhexyl) phthalate (DEHP) was from 0.31 to 3.3 ng g −1 for samples containing up to 10.8% fat. This method was sufficiently sensitive to detect di-(2-ethylhexyl) phthalate, dibutyl phthalate (DBP) and diethyl phthalate (DEP) in two groups of raw cow milk samples (cow milk samples collected using and without using PVC tubing). While similar levels were found in both types of samples for DBP and DEP, the level of DEHP was much higher in samples collected using PVC tubing (215.36 ng g −1) than once without (16.04 ng g −1), indicating potential leaching of DEHP from PVC tubing into raw cow milk.

Volatile flavour components of mandarin wine obtained from clementines (Citrus reticula Blanco) extracted by solid‐phase microextraction

AbstractThe volatile flavour constituents of mandarin wine obtained from clementine (Citrus reticula Blanco) were analysed by headspace solid‐phase microextraction (HS‐SPME) and immersion solid‐phase microextraction (Im‐SPME) coupled to GC–MS. A total of 19 volatiles, including eight esters, four higher alcohols, three monoterpenes and four furfural compounds, were identified in wine. The HS‐SPME technique showed a higher sensitivity than Im‐SPME. The major constituents found in wine volatiles using HS‐SPME were ethyl octanoate, ethyl decanoate, isoamyl alcohol, ethyl hexanoate and isoamyl acetate, respectively. Copyright © 2004 John Wiley & Sons, Ltd.

Application of solid-phase microextraction (spme) for photocatalytic studies of fenitrothion and methyl parathion in aqueous TiO2 suspensions

The photocatalytic degradation of the organophosphorus insecticides fenitrothion and methyl parathion has been studied in aqueous titanium dioxide TiO2 suspensions under simulated solar irradiation. The degradation kinetics followed a pseudo-first-order reaction and has been monitored by headspace solid-phase microextraction (HS-SPME) and gas chromatographic techniques (GC-FTD). Degradation of both insecticides has been a rapid process with half-lives varied between 3.7 and 12.9 min depending on the TiO2 concentration as well as on the structure of the compound. The generated transformation by-products formed during the process were extracted by SPME used in two approaches: (a) by direct immersion in the filtered sample and (b) by exposing the fiber in the sample headspace. The intermediates were formed predominately via oxidation processes and were identified by gas chromatography and mass spectroscopy techniques.

Optimization of headspace solid-phase microextraction conditions for the determination of organophosphorus insecticides in olive oil

A method based on headspace solid-phase microextraction (HS-SPME) technique followed by gas chromatography with flame thermionic detection was developed for the determination of seven organophosphorus (OP) insecticide residues in olive oil samples. The extraction capacity of four fiber coatings, polyacrylate (PA 85 µm), poly(dimethylsiloxane) (PDMS 100 µm), carbowax-divinylbenzene (CW-DVB 65 µm) and poly(dimethylsiloxane)divinylbenzene (PDMS-DVB 65 µm), have been studied and compared. The method was developed using spiked olive oil samples in the concentration range 0.025 to 0.5 mg/L. The PDMS 100-µm fiber showed good extraction efficiency for the target compounds. An increase in the extraction efficiency of OP insecticides was observed when the parameters affecting the HS-SPME process such as temperature, extraction time, salt additives and stirring rate were optimized. Good linearity was observed for the compounds in the tested concentration range. The limits of detection were between 0.005 and 0.01 µg/L.

Analysis of the volatile components of five Turkish Rhododendron species by headspace solid-phase microextraction and GC-MS (HS-SPME-GC-MS).

Volatile constituents of various solvent extracts (n-hexane, CH2Cl2, H2O) of 15 different organs (leaves, flowers, fruits) of five Rhododendron species (Ericaceae) growing in Turkey were trapped with headspace solid-phase microextraction (HS-SPME) technique and analyzed by GC-MS. A total of 200 compounds were detected and identified from organic extracts, while the water extracts contained only traces of few volatiles. The CH2Cl2 extract of the R. luteum flowers was found to exhibit the most diverse composition: 34 compounds were identified, with benzyl alcohol (16.6%), limonene (14.6%) and p-cymene (8.4%) being the major compounds. The CH2Cl2-solubles of R. x sochadzeae leaves contained only phenyl ethyl alcohol. This study indicated appreciable intra-specific variations in volatile compositions within the genus. Different anatomical parts also showed altered volatile profiles. This is the first application of HS-SPME-GC-MS on the volatiles of Rhododendron species.

Headspace solid-phase microextraction (HS-SPME): a microscale sampling technique for determination of monoterpene hydrocarbons in coniferous needles by gas chromatography/mass spectrometry (GC/MS)

A headspace solid-phase microextraction (HS-SPME) technique has been applied for the microscale sampling (single needle for Picea omorica, two needles of Picea abies) of volatile monoterpene hydrocarbons (MTHs) from conifer needles. A simple device consisting of a closed headspace vial equipped with an integral cutting device was used for the collection, homogenisation, and HS-SPME sampling. The highly sensitive gas chromatographic/mass spectrometric (GC/MS) analyses (LODs in tenths of ng g(-1) FW were obtained for 3xS/N criteria) of individual needles confirmed the space distribution of MTHs in different parts of a single sprout (base, centre, apex) and among the left, central and right sprout of a whorl. The highest concentrations of MTHs were found in the apical (leading) sprout (S) of a whorl. The serious increase of MTHs content near the base of the left (SNL) sprout and nearly zero concentrations in the central parts of both the side sprouts of P. abies corresponded to the morphology of the whorl. On the other hand, similar concentrations of MTHs were found in the apex of the side (SNL and SNR) sprouts. The distributions of MTHs obtained after HS-SPME and solvent extraction followed the similar trends for both species. HS-SPME is more suitable for the evaluation of distribution of volatiles in microscale experiments due to the more precise separation of needles into correct categories and elimination of "averaging" effects of the larger quantities of needles needed for the solvent extraction. The precision was improved by one order of magnitude due to the reduction of uncontrolled losses of volatile species during the sample treatment.

Headspace solid-phase microextraction analysis of 3-alkyl-2-methoxypyrazines in wines

A procedure to determine 3-alkyl-2-methoxypyrazines in wines is described. It is based on the headspace solid-phase microextraction (HS-SPME) technique after a clean-up of the sample by distillation (previously acidified to pH 0.5) to remove ethanol and other volatile compounds that can interfere in the SPME. Determination is performed by means of capillary gas chromatography using a nitrogen–phosphorus detector. The method allows quantification of 3-isobutyl-2-methoxypyrazine, 3- sec-butyl-2-methoxypyrazine and 3-isopropyl-2-methoxypyrazine at their natural concentration levels and below their sensory thresholds in Cabernet Sauvignon and Merlot wines. The method was successfully applied to experimental red wines and the evolution of their pyrazine contents during the winemaking process was monitored. Pyrazine content increased during the first maceration day but did not change significantly during alcoholic and malolactic fermentation. Final contents in wines were 12–27 ng/l of 3-isobutyl-2-methoxypyrazine and 5–10 ng/l of 3- sec-butyl-2-methoxypyrazine