Automated headspace solid-phase dynamic extraction to analyse the volatile fraction of food matrices

High concentration capacity headspace techniques (headspace solid-phase microextraction (HS-SPME) and headspace sorptive extraction (HSSE)) are a bridge between static and dynamic headspace, since they give high concentration factors as does dynamic headspace (D-HS), and are as easy to apply and as reproducible as static headspace (S-HS). In 2000, Chromtech (Idstein, Germany) introduced an inside-needle technique for vapour and liquid sampling, solid-phase dynamic extraction (SPDE), also known as "the magic needle". In SPDE, analytes are concentrated on a 50 microm film of polydimethylsiloxane (PDMS) and activated carbon (10%) coated onto the inside wall of the stainless steel needle (5 cm) of a 2.5 ml gas tight syringe. When SPDE is used for headspace sampling (HS-SPDE), a fixed volume of the headspace of the sample under investigation is sucked up an appropriate number of times with the gas tight syringe and an analyte amount suitable for a reliable GC or GC-MS analysis accumulates in the polymer coating the needle wall. This article describes the preliminary results of both a study on the optimisation of sampling parameters conditioning HS-SPDE recovery, through the analysis of a standard mixture of highly volatile compounds (beta-pinene, isoamyl acetate and linalool) and of the HS-SPDE-GC-MS analyses of aromatic plants and food matrices. This study shows that HS-SPDE is a successful technique for HS-sampling with high concentration capability, good repeatability and intermediate precision, also when it is compared to HS-SPME.     

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.     

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.     

Reliability of fibres in solid-phase microextraction for routine analysis of the headspace of aromatic and medicinal plants

This article evaluates the HS-SPME recovery repeatability, intermediate precision and their performance over time when applied to HS-SPME sampling for quality control of medicinal and aromatic plants. Experiments were carried out on two sets of fibres coated with two different coatings and belonging to different lots (i.e 100 microm polydimethylsyloxane (PDMS) and Carboxen/divinylbenzene/PDMS 50/30 microm, l: 1 cm (CAR/DVB/PDMS)) and on chamomile (Matricaria chamomilla L.), sage (Salvia lavandulifolia Vahl.) and a standard solution containing 3-hexanol, isoamyl acetate, 1,8-cineole and menthol in diisobutyl phthalate. The performance of each set of fibres was evaluated by determining a group of complementary statistical parameters including: (i) repeatability of the absolute areas of each marker from each matrix with each fibre; (ii) intra-fibre repeatability of the total absolute areas of the markers of each matrix obtained with each fibre of each set; (iii) inter-fibre intermediate precision of the total absolute areas of the markers of each matrix obtained with all fibres of each set; and (iv) analysis of variance by one-way ANOVA with Fisher and Tukey tests. The influence of the number of analyses on fibre effectiveness (fibre life-time) was studied by linear regression analysis (LRA). The results proved that HS-SPME can successfully be used for routine control analysis of aromatic ad medicinal plants since both types of fibres showed good repeatability and intermediate precision of analytes recovery and consistency over time. Unlike data previously reported by other authors, CAR/DVB/PDMS coated fibres gave better results than those coated with PDMS. The fibre-life seemed mainly to be influenced by the number and conditions of samplings and nature of the matrix investigated.     

Studies on the aroma of cupuassu liquor by headspace solid-phase microextraction and gas chromatography

Headspace solid-phase microextraction (HS-SPME) coupled to gas chromatography with ion trap mass spectrometric detection and with atomic emission detection (GC-AED) was employed to identify possible odor-impact volatile organic compounds in cupuassu (Theobroma grandiflorum Spreng) liquor, as well as to quantify alkylpyrazines present in these samples. SPME fibers coated with 100 microm polydimethylsiloxane (PDMS), 65 microm PDMS-divinylbenzene (DVB) and 75 microm Carboxen (CAR)-PDMS were tested, the later being chosen for the optimized extraction procedure. The principal compounds found in the sample headspace were 3-methylbutanal, dimethylsulfide, dimethyldisulfide, beta-linalool and several alkylpyrazines (notably tetramethylpyrazine). The procedure for quantitation of the alkylpyrazines, using GC-AED for their separation and detection, allowed the detection of microg g(-1) levels of the analytes in the samples, with acceptable precision (R.S.D. less than 10%).     

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.     

Determination of aldehydes in drinking water using pentafluorobenzylhydroxylamine derivatization and solid-phase microextraction

A headspace solid-phase microextraction (HS-SPME) procedure followed by gas chromatography and electron capture detection (GC-ECD) has been developed for the determination of aldehydes in drinking water samples at microg/l concentrations. A previous derivatization with o-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine hydrochloride (PFBHA) was performed due to the high polarity and instability of these ozonation by-products. Several SPME coatings were tested and the divinylbenzene-polydimethylsiloxane (DVB-PDMS) coating in being the most suitable for the determination of these analytes. Experimental SPME parameters such as selection of coating, sample volume, addition of salt, extraction time and temperature of desorption were studied. Analytical parameters such as precision, linearity and detection limits were also determined. HS-SPME was compared to liquid-liquid microextraction (proposed in US Environmental Protection Agency Method 556) by analyzing spiked water samples; a good agreement between results obtained with both techniques was observed. Finally, aldehydes formed at the Barcelona water treatment plant (N.E. Spain) were determined at levels of 0.1-0.5 microg/l. As a conclusion, HS-SPME is a powerful tool for determining ozonation by-products in treated water.     

Analysis of volatile contaminants in vegetable oils by headspace solid-phase microextraction with carboxen-based fibres

The headspace solid-phase microextraction (HS-SPME) efficiencies from vegetable oil of the recently available Carboxen-poly(dimethylsiloxane) (PDMS) and divinylbenzene-Carboxen-PDMS fibres were found to be much greater than those of the PDMS fibre for a number of volatile contaminants. Using these Carboxen-based fibres, the commonly used HS-SPME equilibration times for aqueous matrices of 30-45 min at room temperature for a number of halogenated and aromatic analytes with volatilities ranging from 1,1-dichloroethylene to hexachlorobenzene were found to be insufficient for the effective extraction of the less volatile analytes from vegetable oil. HS-SPME at 100 degrees C for 45 min, followed by rapid cooling to 0 degrees C with a 10 min continuing extraction, however, significantly increased the SPME efficiencies for the less volatile analytes. Spiking solutions were prepared in vegetable oil instead of methanol as the latter was found to displace analytes from the Carboxen material. Using either of the Carboxen-based fibres and SPME at 100 degrees C, all the target analytes could be determined at low or sub-microg kg(-1) with repeatability < or =10%, even though an equilibrium SPME of the less volatile analytes was not achieved.     

Zinc oxide/polypyrrole nanocomposite as a novel solid phase microextraction coating for extraction of aliphatic hydrocarbons from water and soil samples

In this work, ZnO/PPy nanocomposite coating was fabricated on stainless steel and evaluated as a novel headspace solid phase microextraction (HS-SPME) fiber coating for extraction of ultra-trace amounts of environmental pollutants; namely, aliphatic hydrocarbons in water and soil samples. The ZnO/PPy nanocomposite were prepared by a two-step process including the electrochemical deposition of PPy on the surface of stainless steel in the first step, and the synthesis of ZnO nanorods by hydrothermal process in the pores of PPy matrix in the second step. Porous structure together with ZnO nanorods with the average diameter of 70 nm were observed on the surface by using scanning electron microscopy (SEM). The effective parameters on HS-SPME of hydrocarbons (i.e., extraction temperature, extraction time, desorption temperature, desorption time, salt concentration, and stirring rate) were investigated and optimized by one-variable-at-a-time method. Under optimized conditions (extraction temperature, 65 ± 1 °C; extraction time, 15 min; desorption temperature, 250 °C; desorption time, 3 min; salt concentration, 10% w/v; and stirring rate, 1200 rpm), the limits of detection (LODs) were found in the range of 0.08–0.5 μg L⁻¹, whereas the repeatability and fiber-to-fiber reproducibility were in the range 5.4–7.6% and 8.6–10.4%, respectively. Also, the accuracies obtained for the spiked n-alkanes were in the range of 85–108%; indicating the absence of matrix effects in the proposed HS-SPME method. The results obtained in this work suggest that ZnO/PPy can be promising coating materials for future applications of SPME and related sample preparation techniques.     

Development of pressurized hot water extraction followed by headspace solid-phase microextraction and gas chromatography-mass spectrometry for determination of ligustilides in Ligusticum chuanxiong and Angelica sinensis

In this work, a simple, rapid, solvent-free, and low-cost method was developed for the determination of ligustilides in traditional Chinese medicines (TCMs), which was based on pressurized hot water extraction (PHWE) followed by headspace solid-phase microextraction (HS-SPME) and gas chromatography-mass spectrometry (GC-MS). The two bioactive compounds Z-ligustilide and E-ligustilide in two common TCMs, viz. Ligusticum chuanxiong and Angelica sinensis, were extracted by water at 150 degrees C and 40 bar, followed by concentration with HS-SPME and detection by GC-MS. PHWE and HS-SPME parameters were investigated and method validation (precision and recovery) was studied. It has been shown that the proposed method provides a powerful approach for quantitative analysis of ligustilides in TCMs. The method was applied to determination of ligustildes in the TCMs from different growing areas. The results indicate that PHWE-HS-SPME-GC-MS is a potential tool for TCM quality assessment.     

Static headspace versus head space solid-phase microextraction (HS-SPME) for the determination of volatile organochlorine compounds in landfill leachates by gas chromatography

The determination of five volatile organochlorine compounds, VOX (chloroform, 1,1,1-trichloroethane, carbon tetrachloride, trichloroethene and tetrachloroethene) in raw landfill leachates and biologically cleansed leachates by GC-MS is investigated. Two extraction and preconcentration procedures were evaluated for recovery of such analies from the samples, including static headspace (HS) and solid phase microextraction by sampling the headspace above the sample (HS-SPME). Optimisation of operating parameters for the best performance of both, sampling and preconcentration techniques was described. Detection limits, time of analysis, precision and linear ranges of both introduction techniques have been established. Application of proposed methods to the determination of the five VOX under study in the above referred samples revealed the absence of such analytes in both leachates. Then both methods were applied to the determination to the five organochlorine compounds under study on spiked leachates samples. While HS-GC-MS offered better analytical precision than HS-SPME-GC-MS, this last technique gave a faster analytical response because no dilution must be done for a reliable VOX determination in landfill leachates. In any case, both sample introduction techniques tested provides excellent recoveries and good analytical precision (ranged from 1 to 3%).     

Comparison of stir bar sorptive extraction and solid-phase microextraction to determine halophenols and haloanisoles by gas chromatography-ion trap tandem mass spectrometry

Solid-phase microextraction by immersion (IS-SPME) and headspace mode (HS-SPME), together with stir bar sorptive extraction (SBSE), have been assayed in combination with gas chromatography-ion trap tandem mass spectrometry (MS/MS) for analysing 2,4,6-trichlorophenol, 2,3,4,6-tetrachlorophenol, 2,4,6-tribromophenol, 2,4,6-trichloroanisole, 2,3,4,6-tetrachloroanisole and 2,4,6-tribromoanisole in different liquid matrices. Once, the optimization of MS/MS fragmentation analysis was carried out, sample enrichment was performed using the three mentioned extraction methods, and comparison through the determination of linearity, and LOD and LOQs were carried out. SBSE and IS-SPME methods described enabled us to determine the target compounds at ng/l levels, concentrations lower than their olfactory threshold, which is not the case of HS-SPME. SBSE showed a higher concentration capability than both SPME techniques, especially when compared to the HS-SPME mode. Thus, SBSE should be the definitive technique to analyse halophenols and haloanisoles in aqueous matrices. SBSE has been also applied to nine aqueous matrices as different as tap water, wines or commercial lemon juice extract.     

Comparison of headspace and direct single-drop microextraction and headspace solid-phase microextraction for the measurement of volatile sulfur compounds in beer and beverage by gas chromatography with flame photometric detection

Three approaches based on headspace single-drop microextraction (HS-SDME), direct single-drop microextraction (Direct-SDME), and headspace solid-phase microextraction (HS-SPME), have been compared for analyzing volatile sulphur compounds (VSCs) in beer and beverage. Procedures and performance of the three methods have been contrasted through the determination of extraction efficiencies, precision, linearity and limits of detection. The overall process of HS-SDME and HS-SPME was applied to GC-FPD determination of five VSCs in beer and beverage.     

Comparative analysis of volatile compounds of ‘fino’ sherry wine by rotatory and continuous liquid-liquid extraction and solid-phase microextraction in conjunction with gas chromatography-mass spectrometry

Different headspace solid-phase microextraction (HS-SPME) methods have been selected and applied to the analysis of volatile compounds in ‘fino’ sherry wine by gas chromatography-mass spectrometry. A method based on rotary and continuous liquid-liquid extraction (LLE) for analysis of these same compounds has been optimised. The best conditions to extract this type of compounds using SPME and LLE were determined and both methods were validated. Both methodologies show adequate detection and quantitation limits, and linear ranges for correctly analysing these compounds. The recoveries obtained were close to 100%, with good repeatability values. The analytical and procedural advantages and disadvantages of these two methods have been compared. In general, SPME presented higher sensitivities. Both analytical methods were used to analyse five samples of ‘fino’ sherry wine supplied by different producers. No significant differences were found between the techniques at a significance level of 5%. The regression coefficients (r²) for analysis using LLE and SPME exceeded 0.94 for all compounds. The LLE procedure is a method with high repeatability and has the possibility of simultaneous extraction of several samples (up to 12), however the SPME technique is a solvent-free method presenting major advantages, such as small sample volume and higher sensitivity and simplicity.     

Simultaneous distillation-extraction of high-value volatile compounds from Cistus ladanifer L

The present paper describes a procedure to isolate volatiles from rock-rose (Cistus ladanifer L.) using simultaneous distillation-extraction (SDE). High-value volatile compounds (HVVC) were selected and the influence of the extraction conditions investigated. The effect of the solvent nature and extraction time on SDE efficiency was studied. The best performance was achieved with pentane in 1 h operation. The extraction efficiencies ranged from 65% to 85% and the repeatability varied between 4% and 6% (as a CV%).The C. ladanifer SDE extracts were analysed by headspace solid phase microextraction (HS-SPME) followed by gas chromatography with flame ionization detection (GC-FID). The HS-SPME sampling conditions such as fiber coating, temperature, ionic strength and exposure time were optimized. The best results were achieved with an 85 μm polyacrylate fiber for a 60 min headspace extraction at 40 °C with 20% (w/v) of NaCl. For optimized conditions the recovery was in average higher than 90% for all compounds and the intermediate precision ranged from 4 to 9% (as CV %). The volatiles α-pinene (22.2 mg g⁻¹ of extract), 2,2,6-trimethylcyclohexanone (6.1 mg g⁻¹ of extract), borneol (3.0 mg g⁻¹ of extract) and bornyl acetate (3.9 mg g⁻¹ of extract) were identified in the SDE extracts obtained from the fresh plant material.     

Application of headspace solid-phase microextraction to the determination of sulphur compounds with low volatility in wines

Headspace solid-phase microextraction (HS-SPME) has been used for determining sulphur compounds with low volatility in wines. With this technique, handling of samples is minimal so undesirable loses and reactions between compounds are prevented. Furthermore, this kind of extraction is fast and does not require any organic solvent. Under optimal conditions, the HS-SPME, using a new fibre coated with Stable Flex divinylbenzene-Carboxen-polydimethylsiloxane, makes possible the quantification of sixteen sulphur compounds with low volatility which may be present in wines. The limits of detection for the analytes studied ranged between 0.05 and 10 microg/l, and the recovery and repeatability found were acceptable. The method developed was successfully applied to determine the concentration of the target analytes in varietal wines from the Catalonian region (Spain) with some aromatic defects such as an odour of rubber, onion, rotten, unpleasant herbaceous, etc. The results show that the contents of the sulphur compounds studied in these wines are higher than in those without defects. This shows a relationship exists between the presence of sulphur compounds and the quality of the wine aroma.     

An improved method for the measurement of the isotope ratio of ethanol in various samples, including alcoholic and non-alcoholic beverages

The isotope ratios of ethanol, an important constituent or ingredient of some foods and various beverages and fuels, provide information about biological and geographical origin and quality. We have developed an improved method for measuring the isotope ratio of ethanol in various samples by gas chromatography-high temperature conversion or combustion-isotope ratio mass spectrometry (GC-TC/C-IRMS) with headspace solid-phase microextraction (HS-SPME). A HS-SPME method was developed by optimizing several different parameters, including salt addition, incubation temperature and time, and extraction time. The HS-SPME method enabled us to determine the isotope ratio at low ethanol concentrations (0.08 mM) in 50 min with good precision (+/-0.3 per thousand for delta(13)C and +/-5 per thousand for deltaD). An advantage of this technique is that it can be adapted for use with samples which have high viscosity and contain many matrix compounds, such as alcoholic and non-alcoholic beverages.     

Optimisation of a headspace-solid-phase micro-extraction method for simultaneous determination of organometallic compounds of mercury,lead and tin in water by gas chromatography–tandem mass spectrometry

In this work, a headspace-solid-phase micro-extraction (HS-SPME) combined with gas chromatography–mass spectrometry (GC–MS) method for multielemental speciation of organometallic compounds of mercury, lead and tin in water samples was upgraded by the introduction of tandem mass spectrometry (MS/MS) as detection technique. The analytical method is based on the ethylation with NaBEt₄ and simultaneous headspace-solid-phase micro-extraction of the derivative compounds followed by GC–MS/MS analysis. The main experimental parameters influencing the extraction efficiency such as derivatisation time, extraction time and extraction temperature were optimized. The overall optimum extraction conditions were the following: a 50 μm/30 μm divinyl-benzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS) SPME fibre, 150 min derivatisation time, 15 min extraction time, sample agitation at 250 rpm and 40 °C extraction temperature. The analytical characteristics of the HS-SPME method combined with GC–MS and GC–MS/MS were evaluated. The combination of both techniques HS-SPME and GC–MS/MS allowed to attain lower limits of detection (4–33 ng l⁻¹) than those obtained by HS-SPME–GC–MS (17–45 ng l⁻¹). The proposed method presented good linear regression coefficients (r² > 0.9970) and repeatability (4.8–21.0%) for all the compounds under study. The accuracy of the method measured as the average percentage recovery of the compounds in spiked river water and seawater samples was higher than 80% for all the compounds studied, except for monobutyltin in the river water sample. A study of the uncertainty associated with the analytical results was also carried out.     

Comparative study of extraction techniques for determination of garlic flavor components by gas chromatography–mass spectrometry

Several sampling techniques based on steam distillation (SD), simultaneous distillation and solvent extraction (SDE), solid-phase trapping solvent extraction (SPTE), and headspace solid-phase microextraction (HS-SPME) have been compared for the determination of Korean garlic flavor components by gas chromatography–mass spectrometry (GC–MS). Diallyl disulfide (57.88%), allyl sulfide (23.59%), and diallyl trisulfide (11.40%) were found to be the predominant flavor components of garlic samples extracted by SDE whereas these components were at levels of 89.77%, 2.43%, and 3.89% when the same sample was extracted by SD, 97.77%, 0.17%, and 0.10% by SPTE, and 97.85%, 0.01%, and 0.01% by HS-SPME using the 50/30-m divinyl benzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS) fiber. Thermal degradation of components such as allyl methyl sulfide, dimethyl disulfide, and thiirane were observed for SDE and SD but not for SPTE or HS-SPME. HS-SPME had several advantages compared with SD, SDE, and SPTE—rapid solvent-free extraction, no apparent thermal degradation, less laborious manipulation, and less sample requirement. Five different fiber coatings were evaluated to select a suitable fiber for HS-SPME of garlic flavor components. DVB/CAR/PDMS was most efficient among the five types of fiber investigated.     

Determination of fluoride in toothpaste using headspace solid-phase microextraction and gas chromatography-flame ionization detection

A new method for determination of fluoride in toothpaste employing the headspace solid-phase microextraction (HS-SPME) followed by gas chromatography/flame ionization detection (GC/FID) has been proposed. It is a development of the method for determination of fluoride using trimethylchlorosilane (TMCS) as the derivatization reagent to form trimethylfluorosilane (TMFS), with the liquid/liquid extraction (LLE) step replaced by HS-SPME. To introduce the latter, it was necessary to determine the conditions of the reaction and to optimize the two stages of the SPME procedure: extraction and desorption. The parameters of the SPME analysis using carboxen/polydimethylsiloxane (CAR/PDMS) fiber were defined and compared with the corresponding ones for the LLE method, used as a reference. Also, these two methods were compared with respect to their linearity, precision, and accuracy. Results from toothpaste analyses using these two methods were highly correlated, indicating the potential to use the SPME extraction as an inexpensive and solventfree alternative to the LLE method.