Headspace Solid-phase Microextraction GC Research Articles

Identification of geographical origin of winter jujube based on GC–MS coupled with machine-learning algorithms

Headspace solid-phase microextraction (HS-SPME) combined with gas chromatography–mass (GC–MS) is the most often used technique for the analysis of volatile organic compounds (VOCs). When coupled with machine-learning algorithms, the two provide the means to differentiate the volatile metabolome of foods from different origins. In this study, the volatile metabolites of winter jujube, a fruit protected by China and the European Union (EU) based on geographical indications (GI), was analyzed by HS-SPME–GC–MS. Extreme gradient boosting (XGBoost) was applied, for the first time, to evaluate differences in winter jujube grown in four distinct regions. Locational differences yielded 33 VOCs that differed by functionality and concentration with a recurrence probability of ≥ 60%. Zhanhua winter jujube contained the most abundant VOCs, with Yuncheng winter jujube the least. The 33 winter jujube VOCs were analyzed by random forest (RF), support vector machine (SVM), and XGBoost to identify the place of origin. The discrimination rates were about 85% using RF, about 93% using SVM, and about 98% with XGBoost. Compared to RF and SVM algorithms, XGBoost was more efficient, producing higher accuracy rates, and providing new opportunities for origin traceability.

Electrospinning composites of polyvinylidene fluoride - carbon black on solid phase microextraction fibers for enhanced detection of volatile organic compounds by gas chromatography-mass spectrometry

Urine contains volatile organic compounds (VOCs) that can be a source of biomarkers for different medical conditions. Headspace solid phase microextraction (HS-SPME) gas chromatography-mass spectrometry (GC–MS) is the gold standard for VOC detection but is time-consuming and expensive. Gas sensors on the other hand are portable and provide rapid results, but qualification of sensing layers is tedious as VOCs need to be tested individually. Our previous study showed that dip coating SPME fibers, using them to extract VOCs from urine and analyzing them by GC–MS is a tool to rapidly characterize sensing elements. The current study aims to extend these findings to demonstrate that HS-SPME GC–MS can identify how electrospinning can enhance the detection of VOCs due to the increased surface area. Herein, previously optimized suspensions of polyvinylidene fluoride-carbon black (PVDF-CB) were deposited on SPME fiber substrates through dip coating and electrospinning, used to extract VOCs from urine and were subject to GC–MS. Electrospinning parameters (applied voltage, flow rate and duration) were optimized, which showed that an applied voltage of 17 kV and a flow rate of 0.25 mL/hr was optimal for electrospinning fibers with 1.5 µm diameter, high coverage and little to no beading. SPME fibers electrospun with PVDF-CB for 10 min were compared to dip coated fibers, and the results showed electrospun fibers had increased efficiency to extract an abundant number of VOCs in urine. These VOCs were enriched when sampled by the electrospun fiber by factors ranging from 1.5 – 5.5. Results also showed that the electrospun fibers had significantly higher reproducibility (p-value < 0.001) relative to dip coated fibers. In summary, electrospinning has the capability of fabricating more sensitive SPME fibers relative to dip coating, and therefore may be utilized in the future for an array of different applications including but not limited to VOC biomarker discovery.

Estimation of Avocado Oil (Persea americana Mill., Greek “Zutano” Variety) Volatile Fraction over Ripening by Classical and Ultrasound Extraction Using HS-SPME–GC–MS

The study of flavors and fragrances is a topic of rising interest from both marketing and scientific perspectives. Over the last few years, the cultivation of avocados has accelerated in Greece, with production levels elevated by 300%. There has been increasing attention from a number of growers and consumers on avocado oil, the volatiles of which form a key part of consumers’ purchase decisions. A previously unevaluated Zutano cultivar was chosen for this study. Extraction of the pulp oil was performed during three phases of ripening using Soxhlet and ultrasound techniques. Headspace-solid-phase microextraction (HS-SPME) and gas chromatography–mass spectrometry (GC–MS) were utilized in order to analyze the isolated volatile fraction. At least 44 compounds, including mainly terpenoids (61.7%) and non-terpenoid hydrocarbons (35.9%), presented in the Zutano variety, while (1S,6S,7S,8S)-1,3-dimethyl-8-propan-2-yltricyclo[4.4.0.02,7]dec-3-ene (a-copaene) and (1R,9S,Z)-4,11,11-trimethyl-8-methylenebicyclo[7.2.0]undec-4-ene (β-caryophyllene) were in higher abundance. The composition of the volatiles was unaffected by the extraction techniques but was influenced by the ripening stage. Thus, during maturation, the volatile fraction fluctuates, with a significantly higher abundance of terpenoids during the fourth day of the ripe stage, whilst it decreases during over-ripening. These findings demonstrate that the Zutano variety can be used to produce an aromatic oil and hence could be used, among others, as an ingredient in cosmetic products.

Optimization and Validation of a Headspace Solid-Phase Microextraction with Comprehensive Two-Dimensional Gas Chromatography Time-of-Flight Mass Spectrometric Detection for Quantification of Trace Aroma Compounds in Chinese Liquor (Baijiu).

The detection of trace aroma compounds in samples with complex matrices such as Chinese liquor (Baijiu) requires a combination of several methods, which makes the analysis process very complicated. Therefore, a headspace solid-phase microextraction (HS-SPME) method coupled with two-dimensional gas chromatography time-of-flight mass spectrometry (GC×GC-TOFMS) was developed for the quantitation of a large number of trace compounds in Baijiu. Optimization of extraction conditions via a series of experiments revealed that dilution of the alcohol content of 8 mL of Baijiu to 5%, followed by the addition of 3.0 g of NaCl and subsequent SPME extraction with DVB/CAR/PDMS fiber coating over 45 min at 45 °C was the most suitable. To check the matrix effects, various model Baijiu matrices were investigated in detail. The quantitative method was established through an optimized model synthetic solution, which can identify 119 aroma compounds (esters, alcohols, fatty acids, aldehydes and ketones, furans, pyrazines, sulfur compounds, phenols, terpenes, and lactones) in the Baijiu sample. The developed procedure provided high recovery (86.79–117.94%), good repeatability (relative standard deviation < 9.93%), high linearity (R2 > 0.99), and lower detection limits than reported methods. The method was successfully applied to study the composition of volatile compounds in different types of Baijiu. This research indicated that the optimized HS-SPME–GC×GC-TOFMS method was a valid and accurate procedure for the simultaneous determination of different types of trace compounds in Baijiu. This developed method will allow an improved analysis of other samples with complex matrices.

A Novel Method for the Analysis of Volatile Organic Compounds (VOCs) from Red Flour Beetle Tribolium castaneum (H.) using Headspace-SPME Technology

Background: The red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) is one of the world’s most serious stored grain insect pests. A method of early and rapid identification of red flour beetle in stored products is urgently required to improve control options. Specific chemical signals identified as Volatile Organic Compounds (VOCs) that are released by the beetle can serve as biomarkers. Methods: The Headspace Solid Phase Microextraction (HS-SPME) technique and the analytical conditions with GC and GCMS were optimised and validated for the determination of VOCs released from T. castaneum. Results: The 50/30 μm DVB/CAR/PDMS SPME fibre was selected for extraction of VOCs from T. castaneum. The efficiency of extraction of VOCs was significantly affected by the extraction time, temperature, insect density and type of SPME fibre. Twenty-three VOCs were extracted from insects in 4 mL flask at 35 ± 1°C for four hours of extraction and separated and identified with gas chromatography-mass spectroscopy. The major VOCs or chemical signals from T. castaneum were 1-pentadecene, p-Benzoquinone, 2-methyl- and p-Benzoquinone, 2-ethyl. Conclusion: This study showed that HS-SPME GC technology is a robust and cost-effective method for extraction and identification of the unique VOCs produced by T. castaneum. Therefore, this technology could lead to a new approach in the timely detection of T. castaneum and its subsequent treatment.

Volatile composition changes in navel orange at different growth stages by HS-SPME–GC–MS

This study investigated the changes in volatile organic compounds (VOCs) of navel orange during fruit maturation. The volatiles in navel orange from July (young fruit period) to November (commercial maturation period) were separated by headspace solid-phase microextraction (HS-SPME) and analyzed using gas chromatography–mass spectrometry (GC–MS). Fifty-seven VOCs were identified and classified into five groups. Through principal component analysis, the samples of different months were discriminated, and one-way analysis of variance showed that 55 volatiles significantly differed during growth. Among the VOCs, the relative concentration of monoterpenes increased with maturity, and D-limonene was the component with the highest content. Similar behavior was exhibited for aldehydes, reaching the maximum content in November. On the contrary, esters decreased its concentration from July to November. The concentration of sesquiterpenes gradually increased, reaching the maximum level between August and November. Moreover, alcohols reached theirs largest content in September, β-Linalool had the highest content among the alcohols. These results provided important theoretical support for the development of navel orange components and comprehensively elucidate the flavor characteristics during the ripening of navel orange.

Quantification of N-Nitrosamines in white Wine using Headspace Solid-phase Microextraction and Gas Chromatography–Mass Spectrometry

Headspace solid-phase microextraction (HS-SPME) was used to quantify the concentrations of N-nitrosodimethylamine, N-nitrosodiethylamine (NDEA), N-nitrosopiperazine (NPIP) and N-nitrosodibutylamine in five white wines produced in different countries worldwide. A gas chromatograph coupled to a mass spectrometer (GC−MS) was used for detection and quantification of N-nitrosoamines (NAms). Two types of NAms were found in the wines studied: N-nitrosodimethylamine and N-nitrosodibutilamine. The concentrations of the NAms found were innocuous in all the cases studied. The effects of the microextraction parameters (equilibrium temperature, extraction temperature, ionic strength and extraction time) on the GC–MS signal obtained from the NAms were evaluated. The HS-SPME–GC–MS method was validated by calculating the linearity, repeatability, limits of detection and quantification. Neither NDEA nor NPIP was detected in any of the samples analyzed. The standard additions method was applied for the quantitation of the found NAms using internal standards.

Analysis of sesquiterpene hydrocarbons in grape berry exocarp (Vitis vinifera L.) using in vivo-labeling and comprehensive two-dimensional gas chromatography-mass spectrometry (GC×GC-MS).

Sesquiterpenes are structurally diverse, potent flavoring substances that significantly influence the aroma profile of grapes (Vitis vinifera L.) at the time of physiological ripening. To investigate these natural compounds, freshly harvested, ripe berries of the red wine variety Lemberger (Vitis vinifera subsp. vinifera L.) were analyzed using comprehensive two-dimensional gas chromatography (GC×GC) coupled to a time-of-flight mass spectrometer (TOF–MS) after headspace-solid phase microextraction (HS-SPME). The identification of structurally complex natural compounds, such as sesquiterpenes from fruits and vegetables, is often reported as “tentative”, as authentic standards are not commercially available for most of the analytes. For this reason, feeding experiments (in vivo labeling) were carried out using the stable isotope-labeled precursors [5,5-2H2]-1-deoxy-ᴅ-xylulose (d2-DOX) and [6,6,6-2H3]-(±)-mevalonolactone (d3-MVL) to clearly identify the volatiles. Based on the recorded mass spectra of the unlabeled and deuterated compounds, mechanisms for sesquiterpene formation in V. vinifera could be proposed and already known pathways could be confirmed or disproved. For example, the HS-SPME–GC×GC–TOF–MS measurements of fed sample material showed that the tricyclic sesquiterpene hydrocarbons α-copaene, β-copaene, α-cubebene, β-cubebene and the bicyclic δ-cadinene were biosynthesized via (S)-(−)-germacrene D rather than via (R)-(+)-germacrene D as intermediate.

Quantitative Analysis of Polycyclic Aromatic Hydrocarbons at Part Per Billion Levels in Fish Oil by Headspace Solid-Phase Microextraction and Gas Chromatography-Mass Spectrometry (HS-SPME-GC-MS).

Headspace solid-phase microextraction (HS-SPME) was used in combination with gas chromatography-mass spectrometry (GC-MS) for the analysis of polycyclic aromatic hydrocarbons (PAH) at part per billion levels in fish oil samples collected from menhaden fish. The method was initially developed using fish oil from capsules spiked with a standard PAH mixture. The final HS-SPME-GC-MS method presented a linear range from 3 to 1,500 ng/g, with precision for most analytes <10% relative standard deviation. The limits of detection varied from 1 to 7 ng/g depending on the analyte. Real sample analysis was done on menhaden fish oil extracted from fish collected off the coasts of New Jersey and Louisiana. Naphthalene, fluorene, fluoranthene, pyrene, anthracene were detected at low levels of 70-180 ng/g in the real samples. The concentrations of PAHs detected in the real samples were well below established levels of concern for PAHs in finfish.

Rapid Plant Volatiles Screening Using Headspace SPME and Person-Portable Gas Chromatography–Mass Spectrometry

Rapid on-site screening of biogenic volatile emissions from leaves of living plants is demonstrated, using headspace solid-phase microextraction (HS-SPME) with a portable gas chromatograph (PGC), fitted with a low-thermal mass (LTM) column equipped with a miniature toroidal ion trap mass spectrometer (ITMS). For field sampling, the study was conducted at the Royal Botanical Garden, Cranbourne, Australia, with the sampling site located in the Peppermint Garden. Twelve designated plants in the families of Asteraceae, Lamiaceae, Myrtaceae, Pittosporaceae, and Rutaceae were chosen for this field study. A customised SPME syringe was used for headspace sampling and sample introduction; leaves were collected into vials, equilibrated, sampled onto a PDMS/DVB-coated fibre, then desorbed in the GC inlet in split mode. A resistively heated LTM, narrow bore (0.1 mm ID) non-polar capillary column heated at 2 °C s−1 to 270 °C, provided fast GC elution with total run time of 3 min. The miniaturised ITMS was operated over a mass range of 40–500 Da. This provided approximation of near-real-time measurement of leaf volatiles released from the plant. For a second study, PGC–ITMS is employed to profile essential oils from experimental hybrid and commercial Humulus lupulus L. (hop) plant extracts in the laboratory, and contrasted with bench-top data. Results were processed by chromatographic fingerprinting using retention times, and MS fragmentation pattern similarity criteria. Unsupervised multivariate analysis was performed to improve specificity for classification of different plant volatiles, yielding loading variables corresponding to chemical differences of the analysed plants. The combination of HS-SPME and portable GC–ITMS proved effective for rapid chemical expression of the plant volatile genotype in the field.

Headspace Solid-Phase Microextraction GC–MS for Rapid Rice Aroma Analysis Using Optimization Tools

A key feature of rice acceptance by consumers is closely related to its aroma. A few decades of research on rice aroma indicated associated difficulties which arise from its complicated volatile composition. Our investigation seeks to resolve this highly complicated aroma profile using an experimental design for headspace solid-phase microextraction GC–MS. The Plackett–Burman methodology was used as a factor screening method for the headspace solid-phase microextraction procedure and GC–MS analysis, and a central composite design was implemented as an optimization methodology for both steps. Optimization of the extraction procedure and GC–MS analysis leads to a highly resolved rice aroma profile resulting in 66 new constituents. A total of 123 constituents were identified by implementing the procedure on Champa rice from the south of Iran.

Odour-active compounds in baby banana Fruit (Musa acuminata AA Simmonds cv. Bocadillo)

ABSTRACTThe contribution of individual compounds to the typical aroma of baby banana cv. Bocadillo fruit would be useful to assess aroma changes caused in the course of fruit processing. Potent odourants in baby banana fruit were determined by combined headspace solid-phase microextraction GC–Olfactometry (HS-SPME-GC–O), solvent-assisted flavour evaporation, gas chromatography−olfactometry (GC–O), gas chromatography-mass spectrometry (GC-MS), aroma extract dilution analysis (AEDA) and calculation of odour activity values. Twenty-three constituents were considered as potentially odour-active compounds contributing to the typical fruit aroma, from which 2-pentyl acetate, 3-methylbutyl acetate, 3-methylbutyl butanoate, 3-methylbutyl 3-methylbutanoate, hexanal, (E)-2-hexenal and 2-pentyl 3-methylbutanoate were the most important contributors to the aroma. HS-SPME-GC-O has a great potential as fast and simple tool to control aroma quality of baby banana fruit.

Quantification of BTEX in Soil by Headspace SPME–GC–MS Using Combined Standard Addition and Internal Standard Calibration

There is a great demand for simple, fast and accurate methods for quantification of volatile organic contaminants in soil samples. Solid-phase microextraction (SPME) has a huge potential for this purpose, but its application is limited by insufficient accuracy caused by a matrix effect. The aim of this research was to develop the method for BTEX quantification in soil using combined standard addition (SA) and internal standard (IS) calibration. Deuterated benzene (benzene-d6) was used as the internal standard for all analytes. The optimized method includes spiking replicate samples with different concentrations of BTEX standards and the same concentration of benzene-d6, equilibration of soil samples at 40 °C during 2 h, and SPME–GC–MS analysis. Precision and accuracy of IS and SA methods were compared on different soil matrices. Combined SA + IS method provided more precise calibration plots compared to the conventional SA calibration. The SA + IS calibration provided more precise and accurate results compared with a reference method based on solvent extraction followed by GC–MS when applied to BTEX quantification in real soil samples (spiked with diesel fuel and aged). Recoveries of BTEX from soil samples spiked with known concentrations of analytes using the developed method were in the range of 73–130% with RSD values less than 15% for all BTEX. The proposed simultaneous standard addition and internal standard approach can be advantageous and adopted for improved quantification of other toxic VOCs in soil.

Effect of different parameters on composition of volatile components of Myristica fragrans seeds extracted by hydrodistillation assisted by microwave and head-space solid-phase micro-extraction

Hydrodistillation assisted by microwave (HDAM) and Head space solid phase micro-extraction (HS-SPME) of Myristica fragrans houtt (MF) were investigated. A kinetic study was performed for MF seeds using two techniques (HDAM: Hydrodistillation assisted by microwave and SDAM: steam distillation assisted by microwave). The effect of the cryogenic grinding (CG) showed differences in yields and composition of volatile oils compared to the simple grinding (SG). HDAM–SG (3.4%) and SDAM–SG (2.55%) allowed extraction of substantial amounts of volatile oils in less time compared with HDAM–CG (4.75%) and SDAM–CG (3.8%). The kinetic study (differential and accumulated yields) of essential oil extraction was quantitatively and qualitatively performed showing a significant variation of composition with the extraction time, especially for accumulated yields such as sabinene (31.48–38.78%), α-pinene (12.74–14.09%) and β-pinene (10.01–12.11%). Similarly, the HS-SPME–GC–MS analysis showed also a significant variation of MF seeds volatile composition according some parameters as the type of fibre coating (PDMS: Polydimethylsiloxane and PDMS–DVB: Polydimethylsiloxane divenylbenzene), particle size, grinding mode and the mass used. The chemical groups (monoterpenoids, aliphatic and aromatic alcohols and esters) showed specific behaviour in SPME analysis. SPME sampling parameters were optimized for these components.

Influence of fumigants on sunflower seeds: Characteristics of fumigant desorption and changes in volatile profiles

Fumigation of transport containers is common practice to protect stored products from pests. Yet little is known about the desorption times and effects of the highly toxic gases used in this process. To shed light on the behavior of fumigants in real food, we treated sunflower seeds (Helianthus annuus L.) with 100ppm phosphine (PH3), methyl bromide (MeBr) or 1,2-dichloroethane (DCE) for 72h. The compound concentrations in the air were then analyzed by thermal desorption/2D gas chromatography coupled to mass spectrometry and flame photometric detection (TD-2D-GC–MS/FPD). A desorption time of several months was observed for DCE, whereas PH3 and MeBr were outgassed in a matter of days. To investigate possible interactions between gases and constituents of the seeds, non-fumigated, fumigated and outgassed samples were analyzed by headspace solid-phase microextraction GC–MS. We observed significantly different volatile profiles in fumigated and subsequently outgassed seeds compared to non-fumigated seeds. Whereas PH3-treated seeds released far more terpenoids, the volatile pattern of seeds exposed to DCE revealed significantly fewer terpenoids but more aldehydes. These changes are likely to affect food aroma characteristics.

The effect of Maillard reaction products and yeast strain on the synthesis of key higher alcohols and esters in beer fermentations

The effect of Maillard reaction products (MRPs), formed during the production of dark malts, on the synthesis of higher alcohols and esters in beer fermentations was investigated by headspace solid-phase microextraction GC–MS. Higher alcohol levels were significantly (p<0.05) higher in dark malt fermentations, while the synthesis of esters was inhibited, due to possible suppression of enzyme activity and/or gene expression linked to ester synthesis. Yeast strain also affected flavour synthesis with Saccharomyces cerevisiae strain A01 producing considerably lower levels of higher alcohols and esters than S288c and L04. S288c produced approximately double the higher alcohol levels and around twenty times more esters compared to L04. Further investigations into malt type-yeast strain interactions in relation to flavour development are required to gain better understanding of flavour synthesis that could assist in the development of new products and reduce R&D costs for the industry.

Optimisation and validation of a HS-SPME–GC–IT/MS method for analysis of carbonyl volatile compounds as biomarkers in human urine: Application in a pilot study to discriminate individuals with smoking habits

A new and simple analytical approach consisting of an automated headspace solid-phase microextraction (HS-SPME) sampler coupled to gas chromatography-ion trap/mass spectrometry detection (GC–IT/MS) with a prior derivatization step with O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine hydrochloride (PFBHA) was developed to detect volatile carbonyl metabolites with low molecular weights in human urine. A central composite design (CCD) was used to optimise the PFBHA concentration and extraction conditions that affect the efficiency of the SPME procedure. With a sample volume of 1mL, optimal conditions were achieved by adding 300mg/L of PFBHA and allowing the sample to equilibrate for 6min at 62°C and then extracting the samples for 51min at the same temperature, using a divinylbenzene/polydimethylsiloxane (DVB/PDMS) fibre. The method allowed the simultaneous identification and quantification of 44 carbonyl compounds consisting of aldehydes, dialdehydes, heterocyclic aldehydes and ketones. The method was validated with regards to the linearity, inter- and intra-day precision and accuracy. The detection limits ranged from 0.009 to 0.942ng/mL, except for 4-hydroxy-2-nonenal (15ng/mL), and the quantification limits varied from 0.029 to 1.66ng/mL, except for butanal (2.78ng/mL), 2-butanone (2.67ng/mL), 4-heptanone (3.14ng/mL) and 4-hydroxy-2-nonenal (50.0ng/mL). The method accuracy was satisfactory, with recoveries ranging from 90 to 107%. The proof of applicability of the methodology was performed in a pilot target analysis of urine samples obtained from 18 healthy smokers and 18 healthy non-smokers (control group). Chemometric supervised analysis was performed using the volatile patterns acquired for these samples and clearly showed the potential of the volatile carbonyl profiles to discriminate urine from smoker and non-smoker subjects. 5-Methyl-2-furfural (p<0.0001), 2-methylpropanal, nonanal and 2-methylbutanal (p<0.05) were identified as potentially useful biomarkers to identify smoking habits.

Effect of SPME extraction conditions and humidity on the release of volatile lipid oxidation products from spray-dried emulsions

The aim of the study was to investigate the effects of headspace solid-phase microextraction (HS-SPME) conditions and relative humidity (RH) on the release of volatile lipid oxidation products from spray-dried emulsions. Two model spray-dried sunflower oil emulsions with a Na-caseinate–maltodextrin matrix were oxidised, stabilised at five RHs and analysed by HS-SPME–GC–MS for volatiles. Increased extraction temperature raised not only the overall release of volatile compounds but also altered the volatile profile. The obtained volatile profiles were dependent on the RH. This was mainly due to the humidity response of the matrix affecting e.g. its binding ability and hydrophilicity. Cross-linking of the emulsifying protein had a minor influence on the release. Both matrix-related factors and extraction conditions should thus be taken into account in interpretation of the HS-SPME results. On the other hand, being sensitive to changes in matrix composition and structure, the HS-SPME allows studying of matrix-related changes in foods.

Preparation, characterization, and applications of a novel solid-phase microextraction fiber by sol-gel technology on the surface of stainless steel wire for determination of poly cyclic aromatic hydrocarbons in aquatic environmental samples

A novel solid-phase microextraction(SPME) fiber was prepared using sol–gel technology with ethoxylated nonylphenol as a fiber coating material. The fiber was employed to develop a headspace SPME–GC–MS method suitable for quantification of 13 polycyclic aromatic hydrocarbons (PAHs) in water samples. Surface characteristics of the fibers were inspected by energy dispersive X-ray (EDX) spectroscopy as well as by scanning electron microscopy (SEM). The SEM measurements showed the presence of highly porous nano-sized particles in the coating. Important parameters affecting the extraction efficiency such as extraction temperature and time, desorption conditions as well as ionic strength have been evaluated and optimized. In the next step, the validation of the new method have been performed, finding it to be specific in the trace analysis of PAHs, with the limit of detection (LOD) ranging from 0.01 to 0.5μgL−1 and the linear range from the respective LOD to 200μgL−1with RSD amounting to less than 8%. The thermal stability of the fibers was investigated as well and they were found to be durable at 280°C for 345min. Furthermore, the proposed method was successfully applied for quantification of PAHs in real water samples.

Optimization of the HS-SPME–GC–IT/MS method using a central composite design for volatile carbonyl compounds determination in beers

An automated headspace solid-phase microextraction (HS-SPME) combined with gas chromatography and ion trap mass spectrometry detection (GC-IT/MS) was developed in order to quantify a large number of carbonyl compounds in beers. Carbonyl compounds were previously derivatized with O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine hydrochloride (PFBHA). Volatile carbonyl compounds associated with staling beer aroma includes alkanals, alkenals, alkadienals, dicarbonyl compounds, Strecker aldehydes, ketones and furans. The HS-SPME was performed using a polydimethylsiloxane/divinylbenzene (PDMS/DVB) fiber. The procedures were optimized for HS-SPME pre-incubation temperature and time, extraction temperature and time, and PFBHA addition. A central composite design was used in the optimization of extraction conditions and PFBHA addition. The volatile compounds showed optimal extraction incubating 5 ml of beer with 700 mg l(-1) of PFBHA for 7 min and extracted for more 20 min at 45 °C. The method was validated with regard to the linearity, repeatability, inter and intra-day precision and accuracy. The method achieved detection limits ranging from 0.003 to 0.510 µg l(-1), except for furans (1.54-3.44 µg l(-1)). The quantification limits varied from 0.010 to 1.55 µg l(-1), except for 2-furfural (4.68 µg l(-1)), 5-methyl-2-furfural (5.82 µg l(-1)) and 5-hyfroxymethylfurfural (10.4 µg l(-1)). Repeatability values of all compounds were lower than 17%. The method accuracy was satisfactory with recoveries ranging from 88% to 114%. The validated method showed to be suitable for a fast and reliable determination of main carbonyl compounds in beers.