Multivariate analysis of the volatile components in tobacco based on infrared‐assisted extraction coupled to headspace solid‐phase microextraction and gas chromatography‐mass spectrometry

A novel infrared‐assisted extraction coupled to headspace solid‐phase microextraction followed by gas chromatography with mass spectrometry method has been developed for the rapid determination of the volatile components in tobacco. The optimal extraction conditions for maximizing the extraction efficiency were as follows: 65 μm polydimethylsiloxane‐divinylbenzene fiber, extraction time of 20 min, infrared power of 175 W, and distance between the infrared lamp and the headspace vial of 2 cm. Under the optimum conditions, 50 components were found to exist in all ten tobacco samples from different geographical origins. Compared with conventional water‐bath heating and nonheating extraction methods, the extraction efficiency of infrared‐assisted extraction was greatly improved. Furthermore, multivariate analysis including principal component analysis, hierarchical cluster analysis, and similarity analysis were performed to evaluate the chemical information of these samples and divided them into three classifications, including rich, moderate, and fresh flavors. The above‐mentioned classification results were consistent with the sensory evaluation, which was pivotal and meaningful for tobacco discrimination. As a simple, fast, cost‐effective, and highly efficient method, the infrared‐assisted extraction coupled to headspace solid‐phase microextraction technique is powerful and promising for distinguishing the geographical origins of the tobacco samples coupled to suitable chemometrics.     

Modified headspace solid‐phase microextraction for the determination of quantitative relationships between components of mixtures consisting of alcohols,esters, and ethers — impact of the vapor pressure difference of the compounds

The quantitative relationship between analytes established by the headspace solid‐phase microextraction procedure for multicomponent mixtures depends not only on the character and strength of interactions of individual components with solid‐phase microextraction fiber but also on their vapor pressure in the applied headspace solid‐phase microextraction system. This study proves that vapor pressure is of minor importance when the sample is dissolved/suspended in a low‐volatility liquid of the same physicochemical character as that of the used solid phase microextraction fiber coating. It is demonstrated for mixtures of alcohols, esters, ethers and their selected representatives by applying a headspace solid‐phase microextraction system composed of Carbowax fiber and sample solutions in polyethyleneglycol. The observed differences in quantitative relations between components of the examined mixtures established by their direct analysis and by modified headspace solid‐phase microextraction are insignificant (F _exp < F _crit). It is explained by a significant diminution in vapor pressure difference between individual components of the examined mixture in the applied headspace solid phase microextraction system due to low components concentration in polyethyleneglycol suspensions (Raoult's law) and due to strong specific interactions of analyte molecules with polyethyleneglycol molecules.     

Graphene‐doped electrochemical copolymer coating of 2,2‐bithiophene and 3‐methylthiophene for the highly effective solid‐phase microextraction of volatile benzene homologues

We report the electrochemical fabrication of a poly(2,2‐bithiophene‐co‐3‐methylthiophene)‐graphene composite coating and its application in the headspace solid‐phase microextraction and gas chromatography determination of benzenes (i.e., bromobenzene, 4‐bromotoluene, 2‐nitrotoluene, 3‐nitrotoluene and 1,2,4‐trichlorobenzene). The coating was uniform and showed cauliflower‐like microstructure. It had high thermal stability (up to 375°C) and could be used for at least 180 times of solid‐phase microextraction without a decrease in extraction performance. Furthermore, it presented high extraction capacity for the benzenes due to the hydrophobic effect and π–π interaction between the analytes and the coating. Under optimized extraction conditions, good linearity (correlation coefficients higher than 0.9946), wide linear range (0.01–50 μg/L), and low limits of detection (5.25–12.5 ng/L) were achieved for these analytes. The relative standard deviation was lower than 5.7% for five successive measurements with one fiber, and the relative standard deviation for fiber‐to‐fiber was 4.9–6.8% (n = 5). The solid‐phase microextraction and gas chromatography method was successfully applied for the determination of three real samples, and the recoveries for standards added were 89.6–106% for nail polish, 85.8–110% for hair dye, and 90–106.2% for correction fluid, respectively.     

Investigation of fragrance stability used in the formulation of cosmetic and hygienic products using headspace solid‐phase microextraction by nanostructured materials followed by gas chromatography with mass spectrometry

A new composite coating of polypyrrole and sodium lauryl ether sulfate was electrochemically prepared on a stainless‐steel wire using cyclic voltammetry. The application and performance of the fiber was evaluated for the headspace solid‐phase microextraction of a fragrance in aqueous bleach samples followed by gas chromatography combined with mass spectrometry to assess the fragrance stability in this kind of household cleaning product. To obtain a stable and efficient composite coating, parameters related to the coating process such as scan rate and numbers of cycles were optimized using a central composite design. In addition, the effects of various parameters on the extraction efficiency of the headspace solid‐phase microextraction process such as extraction temperature and time, ionic strength, sample volume, and stirring rate were investigated by experimental design methods using Plackett–Burman and Doehlert designs. The optimum values of 53°C and 28 min for sample temperature and time, respectively, were found through response surface methodology. Results show that the combination of polypyrrole and sodium lauryl ether sulfate in a composite form presents desirable opportunities to produce new materials to study fragrance stability by headspace solid‐phase microextraction.     

Inhibiting sorbent stripping by designing a sorbent‐packed porous probe for headspace solid‐phase microextraction

To prevent the stripping of coating sorbents in headspace solid‐phase microextraction, a porous extraction probe with packed sorbent was introduced by using a porous stainless steel needle tube and homemade sol–gel sorbents. The traditional stainless‐steel needle tube was punched by a laser to obtain two rows of holes, which supply a passageway for analyte vapor during extraction and desorption. The sorbent was prepared by a traditional sol–gel method with both poly(ethylene glycol) and hydroxy‐terminated silicone oil as coating ingredients. Eight polycyclic aromatic hydrocarbons and six benzene series compounds were used as illustrative semi‐volatile and volatile organic compounds in sequence to verify the extraction performance of this porous headspace solid‐phase microextraction probe. It was found that the analysis method combining a headspace solid‐phase microextraction probe and gas chromatography with mass spectrometry yielded determination coefficients of no less than 0.985 and relative standard deviations of 4.3–12.4%. The porous headspace solid‐phase microextraction probe showed no decrease of extraction ability after 200 uses. These results demonstrate that the packed extraction probe with porous structure can be used for headspace solid‐phase microextraction. This novel design may overcome both the stripping and breakage problems of the conventional coating fiber.     

Solid‐phase microextraction Arrow for the volatile organic compounds in soy sauce

A novel solid‐phase microextraction Arrow was used to separate volatile organic compounds from soy sauce, and the results were verified by using gas chromatography with mass spectrometry. Solid‐phase microextraction Arrow was optimized in terms of three extraction conditions: type of fiber used (polydimethylsiloxane, polyacrylate, carbon wide range/polydimethylsiloxane, and divinylbenzene/polydimethylsiloxane), extraction temperature (40, 50, and 60°C), and extraction time (10, 30, and 60 min). The optimal solid‐phase microextraction Arrow conditions were as follows: type of fiber = polyacrylate, extraction time = 60 min, and extraction temperature = 50°C. Under the optimized conditions, the solid‐phase microextraction Arrow was compared with conventional solid‐phase microextraction to determine extraction yields. The solid‐phase microextraction Arrow yielded 6–42‐fold higher levels than in solid‐phase microextraction for all 21 volatile organic compounds detected in soy sauce due to the larger sorption phase volume. The findings of this study can provide practical guidelines for solid‐phase microextraction Arrow applications in food matrixes by providing analytical methods for volatile organic compounds.     

A novel sorbent based on carbon nanotube/amino‐functionalized sol–gel for the headspace solid‐phase microextraction of α‐bisabolol from medicinal plant samples using experimental design

A novel sol–gel coating on a stainless‐steel fiber was developed for the first time for the headspace solid‐phase microextraction and determination of α‐bisabolol with gas chromatography and flame ionization detection. The parameters influencing the efficiency of solid‐phase microextraction process, such as extraction time and temperature, pH, and ionic strength, were optimized by the experimental design method. Under optimized conditions, the linear range was between 0.0027 and 100 μg/mL. The relative standard deviations determined at 0.01 and 1.0 μg/mL concentration levels (n = 3), respectively, were as follows: intraday relative standard deviations 3.4 and 3.3%; interday relative standard deviations 5.0 and 4.3%; and fiber‐to‐fiber relative standard deviations 6.0 and 3.5%. The relative recovery values were 90.3 and 101.4% at 0.01 and 1.0 μg/mL spiking levels, respectively. The proposed method was successfully applied to various real samples containing α‐bisabolol.     

Comparison of headspace solid‐phase microextraction and solvent extraction method for the simultaneous analysis of various soil fumigants in soil or water by gas chromatography–mass spectrometry

The quantity of soil fumigants has increased globally that has focused attention on their environmental behavior. However, simultaneous analysis of traces of fumigant residues is often unreported because analysis methods are not readily available to measure them at low concentrations. In this study, typical solvent extraction methods were compared with headspace solid‐phase microextraction methods. Both methods can be used for simultaneously measuring the concentrations of five commonly used soil fumigants in soil or water. The solvent extraction method showed acceptable recovery (76–103%) and intraday relative standard deviations (0.8–11%) for the five soil fumigants. The headspace solid‐phase microextraction method also showed acceptable recovery (72–104%) and precision rates (1.3–17%) for the five soil fumigants. The solvent extraction method was more precise and more suitable for analyzing relatively high fumigant residue levels (0.05–5 μg/g) contained in multiple soil samples. The headspace solid‐phase microextraction method, however, had a much lower limits of detection (0.09–2.52 μg/kg or μg/L) than the solvent extraction method (5.8–29.2 μg/kg), making headspace solid‐phase microextraction most suitable for trace analysis of these fumigants. The results confirmed that the headspace solid‐phase microextraction method was more convenient and sensitive for the determination of fumigants to real soil samples.     

Solvent‐free method for the determination of lignin‐derived phenols in sediments

A solvent‐free method that uses headspace solid‐phase microextraction and gas chromatography with flame ionization detection is proposed for the determination of lignin‐derived phenols in sediments. The extraction and derivatization conditions for the simultaneous analysis of acetosyringone, acetovanillone, syringaldehyde, vanillin, ferulic acid, syringic acid, vanillic acid, p‐hydroxybenzoic acid, and p‐coumaric acid were optimized using a central composite design. After optimization, the best results were obtained with the following conditions: exposure of the polyacrylate fiber to the headspace with 60 μL of N ,O‐bis(trimethylsilyl)trifluoroacetamide as a derivatizing agent for 15 min and then extraction in the headspace of 100 mg of sediment (previously spiked with lignin‐derived phenols) for 35 min. The accuracy of the method was estimated based on recovery tests at two concentration levels and by comparison with a high‐performance liquid chromatography method reported in the literature. Based on the t‐test with a confidence level of 95%, no statistical differences were observed. The detection and quantification limits for the target compounds varied according to their characteristics: values at the microgram per gram level for nonacid compounds and milligram per gram level for phenolic acids, due to the lower volatility of the derivatives.     

An in‐needle solid‐phase microextraction device packed with etched steel wires for polycyclic aromatic hydrocarbons enrichment in water samples

A novel, low‐cost and effective in‐needle solid‐phase microextraction device was developed for the enrichment of trace polycyclic aromatic hydrocarbons in water samples. The in‐needle solid‐phase microextraction device could be easily assembled by inserting hydrofluoric acid‐etched wires, which were used as adsorbent, into a 22‐gauge needle tube within spring supporters. Compared with the commercial solid‐phase microextraction fiber, the developed device has higher efficiency for the extraction of polycyclic aromatic hydrocarbons with four to six rings from water samples using the optimized extraction conditions. With gas chromatography equipped with a flame ionization detector, the limits of detection for the polycyclic aromatic hydrocarbons with four to six rings ranged from 0.0020 to 0.0067 ng/mL. The relative standard deviations for one needle and needle‐to‐needle extractions were in the range of 5.2–9.9% (n = 5) and 3.4–12.3% (n = 5), respectively. The spiked recoveries of the polycyclic aromatic hydrocarbons in tap water samples ranged from 73.2 to 95.4%. This in‐needle solid‐phase microextraction device could be a good field sampler because of the low sample loss over a long storage time.     

Improvement of solid‐phase microextraction efficiency by the application of a carbon‐nanotubes‐based ternary microextraction fiber composite

In this study, a novel technique is proposed for preparation of an efficient and unbreakable metal‐wire‐supported solid‐phase microextraction fiber. A sol–gel film was deposited on electrophoretically deposited carbon nanotubes on a stainless‐steel wire. The applicability of the fiber was evaluated through the extraction of some aromatic pollutants as model compounds from the headspace of aqueous samples in combination with gas chromatography and mass spectrometry. The parameters affecting the structure and extraction efficiency of the fiber (including the type of solvent, time, and potential for electrophoretic deposition) and the parameters affecting the extraction efficiency (such as coating type, salt content, extraction temperature, and time) were investigated. The results showed that the film thickness will be increased by increasing the potential and time duration. Finally, the characterization of the deposited film was accomplished by scanning electron microscopy and thermogravimetric analysis. After the optimization of the extraction parameters, the limit of detection of less than 20 pg/mL was achieved, and the calibration curves were all linear (r ² ≥ 0.9737), in the range from 50 to 500 pg/mL. The solid‐phase microextraction fiber has a high mechanical strength; good stability and long service life, making it potentially applicable in the extraction of trace polycyclic aromatic hydrocarbons from aqueous samples.     

Automated headspace solid‐phase microextraction and on‐fiber derivatization for the determination of clenbuterol in meat products by gas chromatography coupled to mass spectrometry

A method was developed for the determination of clenbuterol in meat using stable‐isotope‐dilution gas chromatography with mass spectrometry coupled with solid‐phase microextraction and on‐fiber derivatization. The samples were first homogenized with hydrochloric acid followed by protein deposition. After headspace solid‐phase microextraction and on‐fiber derivatization, the content of clenbuterol was measured with the aid of stable‐isotope dilution. The condition of solid‐phase microextraction was optimized by central composite design. The relative standard deviations, limit of detection, and recoveries for clenbuterol were 4.2–9.2%, 0.48 μg/kg, and 96–104%, respectively. The proposed method was satisfactory for analysis of real samples as compared with the Chinese standard method.     

Rapid determination of the volatile components in tobacco by ultrasound‐microwave synergistic extraction coupled to headspace solid‐phase microextraction with gas chromatography‐mass spectrometry

An ultrasound‐microwave synergistic extraction coupled to headspace solid‐phase microextraction was first employed to determine the volatile components in tobacco samples. The method combined the advantages of ultrasound, microwave, and headspace solid‐phase microextraction. The extraction, separation, and enrichment were performed in a single step, which could greatly simplify the operation and reduce the whole pretreatment time. In the developed method, several experimental parameters, such as fiber type, ultrasound power, and irradiation time, were optimized to improve sampling efficiency. Under the optimal conditions, there were 37, 36, 34, and 36 components identified in tobacco from Guizhou, Hunan, Yunnan, and Zimbabwe, respectively, including esters, heterocycles, alkanes, ketones, terpenoids, acids, phenols, and alcohols. The compound types were roughly the same while the contents were varied from different origins due to the disparity of their growing conditions, such as soil, water, and climate. In addition, the ultrasound‐microwave synergistic extraction coupled to headspace solid‐phase microextraction method was compared with the microwave‐assisted extraction coupled to headspace solid‐phase microextraction and headspace solid‐phase microextraction methods. More types of volatile components were obtained by using the ultrasound‐microwave synergistic extraction coupled to headspace solid‐phase microextraction method, moreover, the contents were high. The results indicated that the ultrasound‐microwave synergistic extraction coupled to headspace solid‐phase microextraction technique was a simple, time‐saving and highly efficient approach, which was especially suitable for analysis of the volatile components in tobacco.     

Metal–organic framework UiO‐67‐coated fiber for the solid‐phase microextraction of nitrobenzene compounds from water

A sol–gel coating technique was applied for the preparation of a solid‐phase microextraction fiber by coating the metal–organic framework UiO‐67 onto a stainless‐steel wire. The prepared fiber was explored for the headspace solid‐phase microextraction of five nitrobenzene compounds from water samples before gas chromatography with mass spectrometric detection. The effects of the extraction temperature, extraction time, sample solution volume, salt addition, and desorption conditions on the extraction efficiency were optimized. Under the optimal conditions, the linearity was observed in the range of 0.015–12.0 μg/L for the compounds in water samples, with the correlation coefficients (r) of 0.9945–0.9987. The limits of detection of the method were 5.0–10.0 ng/L, and the recoveries of the analytes from spiked water samples for the method were in the range of 74.0–102.0%. The precision for the measurements, expressed as the relative standard deviation, was less than 11.9%.     

Sensitive determination of polychlorinated biphenyls in environmental water samples by headspace solid‐phase microextraction with bamboo charcoal@iron oxide black fibers prior to gas chromatography with tandem mass spectrometry

We have investigated the feasibility of bamboo charcoal@iron oxide black for the headspace solid‐phase microextraction of polychlorinated biphenyls in environmental water samples. Bamboo charcoal@iron oxide black was prepared and used as a solid‐phase microextraction coating material, and gas chromatography with tandem mass spectrometry was used for detection. Several important factors affecting the extraction efficiency were systematically investigated and optimized. Under the optimum conditions, the experimental data exhibited wide linear range over the range 0.2–1000 ng/L and low limits of detection in the range of 4.7–22.2 pg/L. The novel coating was successfully used for the enrichment and determination of polychlorinated biphenyls in real environmental water samples. All these results indicated that bamboo charcoal@iron oxide black‐based headspace solid‐phase microextraction coupled to gas chromatography with tandem mass spectrometry was an excellent alternative for the sensitive analysis of polychlorinated biphenyls at ultratrace levels in the environment.     

Exploring multiple‐cumulative trapping solid‐phase microextraction for olive oil aroma profiling

Headspace solid‐phase microextraction is a solvent‐free sample preparation technique that is based on the equilibrium among a three‐phase system, i.e., sample‐headspace‐fiber. A compromise between sensitivity and extraction time is usually needed to optimize the sample throughput, especially when a large number of samples are analyzed, as usually the case in cross‐samples studies. This work explores the capability of multiple‐cumulative trapping solid‐phase microextraction on the characterization of the aroma profiling of olive oils, exploiting the automation capability of a novel headspace autosampler. It was shown that multiple‐cumulative solid‐phase microextraction has the potential to improve the overall sensitivity and burst the level of information for cross‐sample studies by using cumulative shorter extraction times.     

Rapid analysis of ultraviolet filters using dispersive liquid–liquid microextraction coupled to headspace gas chromatography and mass spectrometry

An ionic‐liquid‐based in situ dispersive liquid–liquid microextraction method coupled to headspace gas chromatography and mass spectrometry was developed for the rapid analysis of ultraviolet filters. The chemical structures of five ionic liquids were specifically designed to incorporate various functional groups for the favorable extraction of the target analytes. Extraction parameters including ionic liquid mass, molar ratio of ionic liquid to metathesis reagent, vortex time, ionic strength, pH, and total sample volume were studied and optimized. The effect of the headspace temperature and volume during the headspace sampling step was also evaluated to increase the sensitivity of the method. The optimized procedure is fast as it only required ∼7–10 min per extraction and allowed for multiple extractions to be performed simultaneously. In addition, the method exhibited high precision, good linearity, and low limits of detection for six ultraviolet filters in aqueous samples. The developed method was applied to both pool and lake water samples attaining acceptable relative recovery values.     

Analysis of volatile organic compounds in pleural effusions by headspace solid‐phase microextraction coupled with cryotrap gas chromatography and mass spectrometry

Headspace solid‐phase microextraction coupled with cryotrap gas chromatography and mass spectrometry was applied to the analysis of volatile organic compounds in pleural effusions. The highly volatile organic compounds were separated successfully with high sensitivity by the employment of a cryotrap device, with the construction of a cold column head by freezing a segment of metal capillary with liquid nitrogen. A total of 76 volatile organic compounds were identified in 50 pleural effusion samples (20 malignant effusions and 30 benign effusions). Among them, 34 more volatile organic compounds were detected with the retention time less than 8 min, by comparing with the normal headspace solid‐phase microextraction coupled with gas chromatography and mass spectrometry method. Furthermore, 24 volatile organic compounds with high occurrence frequency in pleural effusion samples, 18 of which with the retention time less than 8 min, were selected for the comparative analysis. The results of average peak area comparison and box‐plot analysis showed that except for cyclohexanone, 2‐ethyl‐1‐hexanol, and tetramethylbenzene, which have been reported as potential cancer biomarkers, cyclohexanol, dichloromethane, ethyl acetate, n‐heptane, ethylbenzene, and xylene also had differential expression between malignant and benign effusions. Therefore, the proposed approach was valuable for the comprehensive characterization of volatile organic compounds in pleural effusions.     

Boronate affinity monolithic column incorporated with graphene oxide for the in‐tube solid‐phase microextraction of glycoproteins

A poly(vinylphenylboronic acid–ethylene glycol dimethacrylate) monolithic material incorporated with graphene oxide was synthesized inside a poly(ether ether ketone) tube. This tube with boronate affinity monolith was coupled with a high‐performance liquid chromatography system through a six‐port valve to construct an online solid‐phase microextraction with high‐performance liquid chromatography system. The performance of this solid‐phase microextraction with high‐performance liquid chromatography system was demonstrated by standard glycoprotein in aqueous samples, namely, horseradish peroxidase. Some parameters that affect the extraction performance were investigated, including sampling rate, pH of sample solution, and sampling volume. Under the optimized conditions, the developed method showed high extraction efficiency toward horseradish peroxidase. The addition of graphene oxide greatly increased the extraction efficiency of boronate affinity monolith for horseradish peroxidase. The limit of detection of the proposed method was as low as 0.01 μg/mL by using ultraviolet detection. The recognition specificity was also evaluated by analyzing the mixture of bovine serum albumin (nonglycoprotein) and horseradish peroxidase. The results showed that this material could selectively extract horseradish peroxidase from the mixture, indicating its good specificity toward glycoproteins. The proposed method was further applied for analyzing rat plasma samples spiked with horseradish peroxidase. Good recovery and repeatability were obtained.     

Determination of Aroclor 1260 in soil samples by gas chromatography with mass spectrometry and solid‐phase microextraction

A novel fast screening method was developed for the determination of polychlorinated biphenyls that are constituents of the commercial mixture, Aroclor 1260, in soil matrices by gas chromatography with mass spectrometry combined with solid‐phase microextraction. Nonequilibrium headspace solid‐phase microextraction with a 100 μm polydimethylsiloxane fiber was used to extract polychlorinated biphenyls from 0.5 g of soil matrix. The use of 2 mL of saturated potassium dichromate in 6 M sulfuric acid solution improved the reproducibility of the extractions and the mass transfer of the polychlorinated biphenyls from the soil matrix to the microextraction fiber via the headspace. The extraction time was 30 min at 100°C. The percent recoveries, which were evaluated using an Aroclor 1260 standard and liquid injection, were within the range of 54.9–65.7%. Two‐way extracted ion chromatogram data were used to construct calibration curves. The relative error was <±15% and the relative standard deviation was <15%, which are respective measures of the accuracy and precision. The method was validated with certified soil samples and the predicted concentrations for Aroclor 1260 agreed with the certified values. The method was demonstrated to be linear from 10 to 1000 ng/g for Aroclor 1260 in dry soil.