Headspace Solid-phase Microextraction Analysis Research Articles

Analytical methods for the screening of potential volatile migrants from acrylic-base adhesives used in food-contact materials

Two different analytical techniques were studied for screening the volatile compounds present in pure adhesives and those from the adhesives in different laminates. Three different adhesive formulations were used for the study, all acrylic-based and supplied by different producers. Laminates with polypropylene and paper, polypropylene and polyethylene, and aluminium and polyethylene as substrates were prepared and studied. Adhesives themselves were acetonitrile extracted and volatiles identified by time-of-flight mass spectrometry based on accurate mass measurement of molecular and main fragments. The volatiles in the films themselves were determined by a headspace solid-phase microextraction analysis followed by gas chromatography-mass spectrometry. Significant differences were found within the adhesive formulations. Compounds detected in the screening were assessed in terms of migration through the laminate polypropylene and paper into polyethylene used as a matrix-simulating food. The concentration of the compounds in the polyethylene ranged from 0.04 to 1.6 µg dm−2 in the polypropylene side, and from 0.27 to 28 µg dm−2 in the paper side. The most toxic compound detected in the screening, 2,4,7,9-tetramethyl-5-decyne-4, was not found in any of the sides. Analytical features were also calculated to provide the conditions for quantitative purposes. Sensitivity was at low ng dm−2 of polyethylene and the relative standard deviation was below 10%.

Pattern recognition and genetic algorithms for discrimination of orange juices and reduction of significant components from headspace solid‐phase microextraction

Orange (Citrus sinensis L.) juice comprises a complex mixture of volatile components that are difficult to identify and quantify. Classification and discrimination of the varieties on the basis of the volatile composition could help to guarantee the quality of a juice and to detect possible adulteration of the product. To provide information on the amounts of volatile constituents in fresh-squeezed juices from four orange cultivars and to establish suitable discrimination rules to differentiate orange juices using new chemometric approaches. Fresh juices of four orange cultivars were analysed by headspace solid-phase microextraction (HS-SPME) coupled with GC-MS. Principal component analysis, linear discriminant analysis and heuristic methods, such as neural networks, allowed clustering of the data from HS-SPME analysis while genetic algorithms addressed the problem of data reduction. To check the quality of the results the chemometric techniques were also evaluated on a sample. Thirty volatile compounds were identified by HS-SPME and GC-MS analyses and their relative amounts calculated. Differences in composition of orange juice volatile components were observed. The chosen orange cultivars could be discriminated using neural networks, genetic relocation algorithms and linear discriminant analysis. Genetic algorithms applied to the data were also able to detect the most significant compounds. SPME is a useful technique to investigate orange juice volatile composition and a flexible chemometric approach is able to correctly separate the juices.

Characterising the release of flavour compounds from chewing gum through HS-SPME analysis and mathematical modelling

The headspace solid-phase microextraction (HS-SPME) technique combined with GC–MS was evaluated to study 33 selected flavour compounds released from chewing gum. The operating conditions of SPME were optimised, including different fibres (PDMS, DVB/CAR/PDMS, PA and PDMS/DVB), sample size, extraction time and temperature. The results indicated that while HS-SPME was a rapid and valuable technique, poor reproducibility occurred under all conditions. It was found that this deficiency could be alleviated by utilising mathematical modelling techniques, an approach which had not been previously used in the analysis of flavour compounds in chewing gum by HS-SPME. Compared to the instrumental analysis data themselves, the models provided more insights to the release behaviour of flavour compounds from chewing gum and the more reproducible kinetic rate constants might be used for comparing the release of different compounds or the same compound under different conditions.

Optimization of headspace solid-phase microextraction for analysis of ethyl carbamate in alcoholic beverages using a face-centered cube central composite design

The headspace solid-phase microextraction (HS-SPME) of ethyl carbamate from alcoholic beverages was optimized for the first time using a face-centered cube central composite design (CCD). The factors expected to influence the extraction process are discussed. Firstly, some of factors are fixed based on the opinion of expert and previous experiments, which reduce the number of factors and then avoid very complex response models and large variability. Secondly, for three remaining inexplicit factors, sample temperature, pH and %NaCl, a face-centered cube central composite design was performed and a response surface equation was derived. The statistical parameters of the derived model were r = 0.974 and F = 20.183. The optimum conditions were obtained using a grid method. Next, the method was analytically evaluated using the optimum conditions. The detection limit, relative standard deviation, linear range and recovery were 3 μg L −1, 4.3–8.6%, 10–160 μg L −1, and 92.8–97.5%, respectively. Finally, the method was applied to a variety of alcoholic beverages.

Screening of variety- and pre-fermentation-related volatile compounds during ripening of white grapes to define their evolution profile

The variety- and pre-fermentation-related volatile compounds of ‘Fernão-Pires’ (FP) white grape berries were analyzed during ripening by headspace-solid phase microextraction (HS-SPME) coupled to gas chromatography-quadrupole mass spectrometry (GC-qMS). A preliminary step, in which the grapes were crushed and macerated before HS-SPME analyses, was used. The sampling started at véraison (beginning of berry ripening) and was carried on during 5 weeks in two different vineyards. Sixteen terpenoids, two C 13 norisoprenoids, two aromatic alcohols, two C 6 aldehydes, and three C 6 alcohols were identified. The amount of all volatiles increased since véraison towards day 20. A sharp decrease was observed after this day. The maximum amount of varietal volatile compounds was coincident with the harvesting day for white table wine production defined by the ratio sugar/acid content. The varietal volatile evolution observed for FP grapes shows that the maximum amount of volatiles occurs only in a very short period. As a consequence, the establishment of the optimum moment for harvesting of FP white variety, based on its volatile content, deserves higher accuracy than that necessary for all other already studied grapes. This work also evidences that the analysis of the evolution of the terpenoids with higher GC peak area can represent the evolution of all varietal compounds. For FP grapes, this work shows that the screening of linalool, α-terpineol, and geraniol during ripening can be used to define the evolution profile of the varietal volatile compounds.

Simultaneous headspace solid phase microextraction analysis of off‐flavour compounds from Quercus suber L. cork

AbstractA headspace solid phase microextraction/gas chromatography/(ion trap) mass spectrometry (HS‐SPME/GC/MS) method was developed for the simultaneous analysis of volatile compounds responsible for off‐flavours in cork‐stoppered wines, namely 3‐methyl‐1‐butanol (3MB), 1‐octen‐3‐ol (OCT3), 1‐octanol (1OCT), guaiacol (GUA), 2‐methylisoborneol (MIB), 2,4,6‐trichloroanisole (TCA) and geosmine (GEO). Extraction temperature, global linearity and linearity, reproducibility and repeatability of each chemical were optimised and interference effects were studied. The optimisation studies showed that an extraction temperature of 30 °C gave the best reproducibility and linearity. The global chromatographic areas were linearly correlated (R2 = 0.9788) with the global matrix concentration between 41.5 and 275.2 mg L−1. The reproducibility and linearity of the studied HS‐SPME methodology indicated coefficients of variation between 3.2 and 8.8% and linear responses to all compounds, with regression coefficients (R2) between 0.9516 and 0.9886. Finally, it has been observed that variation of the concentration of 1OCT causes significant variation in the chromatographic areas of the other compounds, with the exception of OCT3. Therefore, if 1OCT is detected at a level that potentially causes interferences in quantification of the other components, new calibration curves must be prepared incorporating an appropriate background concentration of this component. Copyright © 2007 Society of Chemical Industry

Influence of the soil matrices on the analytical performance of headspace solid-phase microextraction for organotin analysis by gas chromatography-pulsed flame photometric detection

Organotin compounds (OTCs) have been identified in a variety of environmental media (air, surface water, groundwater, soil and sediments). In the past, much attention was assigned to the study of the OTCs content in biological samples, water and sediments. Little information about OTCs in soil is available. In this work, a procedure for butyl and phenyltin determination in soils by headspace-solid-phase microextraction (HS-SPME) gas chromatography-pulsed flame photometric detection (GC-PFPD) was investigated. For SPME analysis, a polydimethylsiloxane (PDMS) coating was applied. Peat soil rich in organic matter and with a high cation-exchange capacity (CEC), and clay soil low in organic matter and with a low CEC were analysed. The influence of these different soil matrices on HS-SPME analysis was evaluated by spiking of samples. In general, the recoveries for the two spiked soils exceeded 80%. The repeatability of the method was better than 10%. The limits of detection (LODs) and limits of quantification (LOQs) were in the ng Sn g −1 range. The technique may be reliably applied for the determination of butyltins and monophenyltin in soils, while it shows some limitations for the analysis of di- and triphenyltin (TPhT).

Sample pretreatment method for the determination of polychlorinated biphenyls in bird livers using ultrasonic extraction followed by headspace solid-phase microextraction and gas chromatography–mass spectrometry

A simple and reliable sample methodology based on simultaneous ultrasonic extraction, sulfuric acid clean-up and headspace solid-phase microextraction (SPME)–gas chromatography–mass spectrometry has been developed as an advantageous analytical tool for the determination of seven polychlorinated biphenyl congeners in bird livers at low levels. The influence of several parameters on the efficiency of the proposed method was systematically investigated. The clean-up efficiency of sulfuric acid treatment was tested and compared with those of column chromatography (Flosiril, silica gel and alumina) and solid-phase extraction (SPE) (Supelclean ENVI-Carb cartridge) procedures. The use of sulfuric acid in the clean-up step prior to headspace solid-phase microextraction analysis allows the removal of interfering matrix compounds present in the liver extracts that would otherwise cause severe ionization suppression of the polychlorinated biphenyls (PCBs) during the ionization process. The optimized method had good linearity ( R 2 > 0.99) over the range studied (5–500 ng/g wet weight) and showed satisfactory level of precision, with RSD values lower than 10.6%. The obtained relative recoveries ranged between 63 and 94%. The limits of detection (0.06–0.63 ng/g wet weight) were low enough to check for harmful levels of polychlorinated biphenyls in biological samples, and were well below most of the restrictive limits established by European Union regulations. The method was found to be reliable under the operational conditions proposed and was applied successfully to the analysis of individual polychlorinated biphenyls in liver tissues. The results obtained from five bird species from Greece revealed the presence of the target compounds in all samples analyzed, at levels ranging between 0.54 and 39.45 ng/g wet weight.

Effect of the matrix volatile composition in the headspace solid-phase microextraction analysis of extra virgin olive oil

The effectiveness of headspace solid-phase microextraction (HS-SPME) for the quantitative analysis of extra virgin olive oil volatiles was investigated on 44 standard compounds, using an adsorbent polydimethylsiloxane/divinylbenzene (PDMS/DVB) fiber. The method’s sensitivity was satisfactory, as was its repeatability. However, when the extraction was carried out on mixtures containing all the standard analytes, phenomena of coating saturation and competition between components caused losses in linearity at lower levels of concentration, thus distorting the quantitative evaluation. Coating saturation or displacement between components was also found to be responsible for the bias in the quantitative determinations when extra virgin olive oil samples were analysed. These limitations were overcome by diluting the oil at concentrations not exceeding the total capacity of the fiber coating and until the quantity of displacing compounds was reduced to sufficiently low levels.

Chemical constituents of volatile fractions from Echinops ellenbeckii O. Hoffm

The essential oil and headspace volatiles from the root, stem, leaf and flower head of Echinops ellenbeckii O. Hoffm. were obtained by steam distillation and headspace solid-phase microextraction (HS-SPME). The samples were then analyzed by gas chromatography-mass spectroscopy (GC-MS). Using the HS-SPME analysis, twenty-eight compounds (20.4 %) were identified in the root, twenty-three (55.4 %) in the stem, nineteen (32.2 %) in the leaf and fourteen (16.0 %) in the flower. From the steam distillate, twenty-two (18.7 %), four (15.4 %), nine (39.7 %) and twenty-eight (92.9 %) compounds were observed in the root, stem, leaf and flower, respectively. Using both methods of extraction, seventy compounds were detected in the whole plant. The main sesquiterpene constituents were β-selinene (3.14 %) in the flower, β-maaliene (4.04 %) in the root, caryophyllene oxide (4.93 %) in the leaf and cyperene (8.64 %) in the root. The root were found to have the largest number of sesquiterpene constituents followed by the flower. Stems and leaves contained few amounts of the terpene compounds and higher proportions of aliphatic hydrocarbons and their oxygenated forms.

Pulp aroma compounds of untreated, boiled and roasted African pear [ Dacryodes edulis (G. Don) H.J. Lam] fruits from Cameroon by HS-SPME analysis coupled with GC/FID and GC/MS

The pulp aroma composition of untreated, boiled and roasted Dacryodes edulis (G. Don) H.J. Lam (Burseraceae) fruits from Cameroon was investigated by headspace solid phase microextraction (HS-SPME) coupled with gas chromatographic-spectroscopic (GC/FID and GC/MS) and olfactoric methods to identify those volatiles responsible for the characteristic aroma of these different samples. In particular, monoterpenes, such as α-pinene (untreated/boiled/roasted fruits: 60.3%/44.9%/37.1%), β-pinene (8.2%/21.1%/16.2%), myrcene (15.0%/7.3%/20.9%), limonene (3.6%/6.3%/3.4%) and sabinene (1.4%/3.8%/1.1%) were found to be main compounds of these essential oils. In addition, dimethyl sulfide (4.1%/7.0%) and hexanal (4.6%/8.1%) could be identified in the pulp headspace of boiled and roasted D. edulis fruits. A correlation of the identified constituents of these three pulp headspace samples of this commonly known “African pear” from Cameroon with their single odor impressions is also given.

Headspace solid-phase microextraction method for the study of the volatility of selected flavor compounds.

Changes in the volatility of selected flavor compounds in the presence of nonvolatile food matrix components were studied using headspace solid-phase microextraction (HS-SPME) combined with GC-MS quantification. Time-dependent adsorption profiles to the SPME fiber and the partition coefficients between different phases were obtained for several individual volatiles, showing that HS-SPME analysis with a short sampling time can be used to determine the "true" headspace concentration at equilibrium between the headspace and a sample matrix. Equilibrium dialysis followed by HS-SPME/GC-MS was carried out to confirm the ability of HS-SPME extraction for monitoring the free volatile compounds in the presence of proteins. In particular, a short sampling time (1 min) avoided additional extraction of volatiles bound to the protein. Interactions between several selected flavor compounds and nonvolatile food matrix components [beta-lactoglobulin or (+)-catechin] were also studied by means of HS-SPME/GC-MS analysis. The volatility of ethyl hexanoate, heptanone, and hexanal was significantly decreased by the addition of beta-lactoglobulin compared to that of isoamyl acetate. Catechin decreased the volatility of ethyl hexanoate and hexanal by 10-20% and increased that of 2-heptanone by approximately 15%. This study indicates that HS-SPME can be a useful tool for the study of the interactions between volatile compounds and nonvolatile matrix components provided the kinetic and thermodynamic behavior of the volatiles in relation to the fiber chosen for the studies is carefully considered.

Automated headspace solid-phase microextraction and capillary gas chromatography analysis of ethanol in postmortem specimens

Solid-phase microextraction (SPME) is a relatively new solventless sample preparation technique that allows simultaneous sampling, extraction, pre-concentration, and introduction of analytes from a sample matrix in a single procedure. This methodology has been used for the analysis of several drugs of forensic toxicology interest including volatile compounds. This paper describes a methodology for analysis of ethanol and other volatile compounds using automatic headspace solid-phase microextraction (HS-SPME) and capillary gas chromatography in postmortem specimens. The methodology was initially developed using standard solutions of acetaldehyde, acetone, methanol, and ethanol. Isobutanol was used as internal standard. Postmortem samples of blood, urine, and vitreous humor were obtained during medico-legal autopsies. To date, there are no published paper regarding alcohol analysis in vitreous humor specimens using HS-SPME and limited literature analyzing blood and urine samples. HS-SPME analysis showed that, under optimized conditions, ethanol and isobutanol (internal standard) were well-separated from other volatile compounds such as acetaldehyde, acetone, and methanol considered to be potential interferents in ethanol analysis. The calibration curves for each volatile compound demonstrated good linearity throughout the concentration range from 0.001 to 1.0g/dl and the detection limit of ethanol in the studied specimens was approximately 0.0001g/dl.

Headspace solid-phase microextraction analysis of aroma compounds in vinegar: Validation study

Headspace solid-phase microextraction (HS-SPME) was evaluated for analysing aromatic compounds in vinegar. The fibre used (a Carboxen–polydimethylsiloxane fibre), and the analytical conditions had been optimised in a previous work. The HS-SPME procedure developed shows detection and quantitation limits, and linear ranges adequate for analysing this type of compounds. The recoveries obtained were close to 100%, with repeatability values lower than 20%. However, considerable differences have been detected between different fibres. The method was applied to a variety of Sherry wine vinegars.

Headspace solid-phase microextraction analysis of volatile components of spices

Headspace solid-phase microextraction (HSSPME) coupled with gas chromatography-mass spectrometry (GC-MS) has been used to isolate volatile compounds from three different spices (basil, oregano, and bay leaves). SPME conditions were optimized before the experimental extractions, to achieve optimum recovery of the volatile compounds. Method reproducibility and linearity were evaluated. Relative standard deviations (RSD) between 1.4 and 9.3% were obtained. Typical components of the essential oils of spices and other plant materials, e.g. terpenes, hydrocarbons, and oxygenated terpenes were identified. These results indicate that headspace SPME coupled with GC-MS is an excellent method for analysis of the odors of spices.

Optimisation of headspace solid-phase microextraction for analysis of aromatic compounds in vinegar

Headspace solid-phase microextraction has been applied to the analysis of aroma compounds in vinegar. Silica fibre coated with Carboxen–polydimethylsiloxane was found to be more efficient at extracting these compounds than other fibres such as those coated with polydimethylsiloxane, Carbowax–divinylbenzene, and polydimethylsiloxane–divinylbenzene, but its repeatability was low. 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. This chemometric tool is very appropriate in screening experiments where the aim is to investigate several possibly influential and/or interacting factors. The extraction efficiency is inversely affected by the acetic acid content—an increase in the acetic acid concentration decreases the extraction efficiency. No interference is observed with the increase in content of polyphenols.

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

Optimization of Headspace Solid-Phase Microextraction for Analysis of Wine Aroma Compounds

Headspace solid-phase microextraction (SPME) is a fast and simple sampling method for analysis of volatile compounds, but quantitation can be affected by sample matrix and sampling conditions. Sampling time and temperature are particularly important in controlling analyte response, and the effects vary for different compound classes and volatilities. Tests with model solutions containing a range of typical wine volatiles show that increasing temperature and sampling time can increase sensitivity for higher boiling polar compounds but decrease sensitivity for very volatile compounds. Sample matrix elements such as ethanol concentration can also have different effects on the responses of different compounds.

Headspace solid-phase microextraction analysis of volatile sulphides and disulphides in wine aroma

Sulphur compounds (S-compounds) are important constituents of wine off-flavours. Headspace solid-phase microextraction (HS-SPME) combined with gas chromatography coupled to flame photometric detection (GC–FPD) was used to develop a suitable method to analyse volatile sulphides and disulphides. This is a very simple and fast technique which gives good reproducibility at μg/l levels (relative standard deviations<10%). The analytes were extracted from the headspace of the samples by using either polydimethylsiloxane or polyacrylate coated fused-silica fibers in an SPME unit. Then, the fiber was inserted into the injector of a gas chromatograph and the extracted S-compounds were thermally desorbed. The influence of different parameters, such as ionic strength, stirring, headspace volume, ethanol concentration, time and temperature of extraction, was studied. The extraction of the fibers varies considerably for the different sulphur compounds studied. The most volatile compounds were the least extracted by the coating fibers tested. The standard additions technique, applied to real samples, gave the recoveries >94%. The detection limits range between 3 μg/l and 50 ng/l. The overall process was successfully applied to identify and quantify S-compounds in white and red wines.

Headspace Solid-Phase Microextraction Analysis of Methyl Isothiocyanate in Wine

Methyl isothiocyanate (MITC) is used as soil fumigant for several vegetable diseases and as antifermentative agent in wine. A new headspace solid phase microextraction (HS-SPME) method for analysis of MITC in wine is here described. This method is fast, inexpensive and does not require any solvent. Moreover, it shows a low minimum detectable limit and a wide linearity range. The quantification of MITC is performed by the standard additions method and does not require the use of internal standard, as in other methods. Keywords: Wine analysis; antifermentative agents; methyl isothiocyanate; HS-SPME