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.     

Environmentally friendly solid‐phase microextraction coupled with gas chromatography and mass spectrometry for the determination of biogenic amines in fish samples

In this work, a facile and environmentally friendly solid‐phase microextraction assay based on on‐fiber derivatization coupled with gas chromatography and mass spectrometry was developed for determining four nonvolatile index biogenic amines (putrescine, cadaverine, histamine, and tyramine) in fish samples. In the assay, the fiber was firstly dipped into a solution with isobutyl chloroformate as derivatization reagent and isooctane as extraction solvent. Thus, a thin organic liquid membrane coating was developed. Then the modified fiber was immersed into sample solution to extract four important bioamines. Afterwards, the fiber was directly inserted into gas chromatography injection port for thermal desorption. 1,7‐Diaminoheptane was employed as internal standard reagent for quantification of the targets. The limits of detection of the method were 2.98–45.3 μg/kg. The proposed method was successfully applied to the detection of bioamines in several fish samples with recoveries ranging 78.9–110%. The organic reagent used for extraction was as few as microliter that can greatly reduce the harm to manipulator and environment. Moreover, the extraction procedures were very simple without concentration and elution procedures, which can greatly simplify the pretreatment process. The assay can be extended to the in situ screening of other pollutant in food safety by changing the derivatization reagent.     

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.     

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.     

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.     

Electrospun polyamide–polyethylene glycol nanofibers for headspace solid‐phase microextration

A solution of polyamide (PA) containing polyethylene glycol (PEG) as a side low‐molecular‐weight polymer was electrospun. After synthesizing the PA–PEG nanofibers, the constituent was subsequently removed (modified PA) and confirmed by Fourier transform infrared spectroscopy. The scanning electron microscopy images showed an average diameter of 640 and 148 nm for PA and PA–PEG coatings, respectively, while the latter coating structure was more homogeneous and porous. The extraction efficiencies of PA, PA–PEG, and the modified PA fiber coatings were assayed by headspace solid‐phase microextraction of a number of chlorophenols from real water samples followed by their determination by gas chromatography with mass spectrometry. To prepare the most appropriate coatings, the amounts and the flow rate of the electrospinning solution were investigated. Various extraction parameters, such as the salt content, desorption condition, extraction temperature, and time were optimized. The limits of detection of the method were in the range of 0.8–25 ng/L, while the RSDs at two concentration levels of 200 and 80 ng/L were between 2.1 and 12.2%. The analysis of real water samples led to relative recoveries between 85 and 98% with a linearity of 8–1500 ng/L.     

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.     

Multiresidue determination of 114 multiclass pesticides in flue‐cured tobacco by solid‐phase extraction coupled with gas chromatography and tandem mass spectrometry

A sensitive and robust multiresidue method for the simultaneous analysis of 114 pesticides in tobacco was developed based on solid‐phase extraction coupled with gas chromatography and tandem mass spectrometry. In this strategy, tobacco samples were extracted with acetonitrile and cleaned up with a multilayer solid‐phase extraction cartridge Cleanert TPT using acetonitrile/toluene (3:1) as the elution solvent. Two internal standards of different polarity were used to meet simultaneous pesticides quantification demands in the tobacco matrix. Satisfactory linearity in the range of 10–500 ng/mL was obtained for all 114 pesticides with linear regression coefficients higher than 0.994. The limit of detection and limit of quantification values were 0.02–5.27 and 0.06–17.6 ng/g, respectively. For most of the pesticides, acceptable recoveries in the range of 70–120% and repeatabilities (relative standard deviation) of <11% were achieved at spiking levels of 20, 100, and 400 ng/g. Compared with the reported multiresidue analytical method, the proposed method provided a cleaner test solution with smaller amounts of pigments, fatty acids as well as other undesirable interferences. The development and validation of the high sensitivity, high selectivity, easy automation, and high‐throughput analytical method meant that it could be successfully used for the determination of pesticides in tobacco samples.     

Determination of eight fatty acid ethyl esters in meconium samples by headspace solid‐phase microextraction and gas chromatography–mass spectrometry

A number of fatty acid ethyl esters (FAEEs) have recently been detected in meconium samples. Several of these FAEEs have been evaluated as possible biomarkers for in utero ethanol exposure. In the present study, a method was optimized and validated for the simultaneous determination of eight FAEEs (ethyl laurate, ethyl myristate, ethyl palmitate, ethyl palmitoleate, ethyl stearate, ethyl oleate, ethyl linoleate and ethyl arachidonate) in meconium samples. FAEEs were extracted by headspace solid‐phase microextraction. Analyte detection and quantification were carried out using GC‐MS operated in chemical ionization mode. The corresponding D5‐ethyl esters were synthesized and used as internal standards. The LOQ and LOD for each analyte were <150 and <100 ng/g, respectively. The method showed good linearity (r²>0.98) in the concentration range studied (LOQ – 2000 ng/g). The intra‐ and interday imprecision, given by the RSD of the method, was lower than 15% for all FAEEs studied. The validated method was applied to 63 authentic specimens. FAEEs could be detected in alcohol‐exposed newborns (>600 ng/g cumulative concentration). Interestingly, FAEEs could also be detected in some non‐exposed newborns, although the concentrations were much lower than those measured in exposed cases.     

Polyurethane/polystyrene‐silica electrospun nanofibrous composite for the headspace solid‐phase microextraction of chlorophenols coupled with gas chromatography

A novel electrospun composite nanofiber‐based adsorbent (polyurethane/polystyrene‐silica) was fabricated, characterized, and used in the headspace solid‐phase microextraction of the acetylated derivatives of chlorophenols in water samples before gas chromatography with micro electron capture detection. The surface morphology, chemical composition, thermal stability, and structure of the fibers were investigated by scanning electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, and Brunauer–Emmett–Teller and Barrett–Joyner–Halenda techniques. The effect of the main parameters influencing the efficiency of the method including extraction temperature, salt concentration, and extraction time was investigated and the optimized conditions were obtained. The linear dynamic ranges were 0.1–800 ng/mL. The relative standard deviations (n = 3) and the limits of detection were 2.64–9.57% and 0.0234–0.830 ng/mL, respectively. The relative recoveries for real samples (river water and sewage of our university campus) were between 90.8 and 111%.     

Fast determination of octinoxate and oxybenzone uv filters in swimming pool waters by gas chromatography/mass spectrometry after solid‐phase microextraction

A fast gas chromatography/mass spectrometry method was developed and validated for the analysis of the potential endocrine disrupters octinoxate and oxybenzone in swimming pool water samples based on the solvent‐free solid‐phase microextraction technique. The low‐pressure gas chromatography/mass spectrometry method used for the fast identification of UV filter substances was compared to a conventional method in terms of sensitivity and speed. The fast method proposed resulted in 2 min runs, leading to an eightfold decrease in the total analysis time and a sevenfold improvement in detection limits. The main parameters affecting the solid‐phase microextraction process were also studied in detail and the optimized conditions were as follows: fiber coating, polyacrylate; extraction mode, direct immersion; extraction temperature, 25°C; sample volume, 5 mL; extraction time 45 min; pH 6.5. Under the optimized conditions, a linear response was obtained in the concentration range of 0.5–25 μg/L with correlation coefficients in the range 0.990–0.999. The limits of detection were 0.17–0.29 μg/L, and the recoveries were 80–83%. Combined method uncertainty was assessed and found to be less than 7% for both analytes for concentrations equal to or higher than 5 μg/L. Pool water samples were analyzed to demonstrate the applicability of the proposed method. Neither octinoxate nor oxybenzone were detected in the swimming pool water samples at concentrations above the respective limits of detection.     

Multivariate optimization of a headspace solid‐phase microextraction method followed by gas chromatography with mass spectrometry for the determination of terpenes in Nicotiana langsdorffii

A simple and sensitive procedure based on headspace solid‐phase microextraction and gas chromatography with mass spectrometry was developed for the determination of five terpenes (α‐pinene, limonene, linalool, α‐terpineol, and geraniol) in the leaves of Nicotiana langsdorffii. The microextraction conditions (extraction temperature, equilibration time, and extraction time) were optimized by means of a Doehlert design. The experimental design showed that, for α‐pinene and limonene, a low temperature and a long extraction time were needed for optimal extraction, while linalool, α‐terpineol, and geraniol required a high temperature and a long extraction time. The chosen compromise conditions were temperature 60°C, equilibration time 15 min and extraction time 50 min. The main analytical figures of the optimized method were evaluated; LODs ranged from 0.07 ng/g (α‐pinene) to 8.0 ng/g (geraniol), while intraday and interday repeatability were in the range 10–17% and 9–13%, respectively. Finally, the procedure was applied to in vitro wild‐type and transgenic specimens of N. langsdorffii subjected to abiotic stresses (chemical and heat stress). With the exception of geraniol (75–374 ng/g), low concentration levels of terpenes were measured (ng/g level or lower); some interesting variations in terpene concentration induced by abiotic stress were observed.     

Determination of anatoxin-a in environmental water samples by solid-phase microextraction and gas chromatography-mass spectrometry

In the present work, a method was developed and optimized aiming at the determination of anatoxin-a in environmental water samples. The method is based on the direct derivatization of the analyte by adding hexylchloroformate in the alkalinized sample (pH = 9.0). The derivatized anatoxin-a was extracted by a solid-phase microextraction (SPME) procedure, submersing a PDMS fiber in an amber vial for 20 min under magnetic stirring. GC-MS was used to identify and quantify the analyte in the SIM mode. Norcocaine was used as internal standard. The following ions were chosen for SIM analyses (quantification ions in italics): anatoxin-a: 191, 164, 293 and norcocaine: 195, 136, 168. The calibration curve showed linearity in the range of 2.5-200 ng/mL and the LOD was 2 ng/mL. This method of SPME and GC-MS analysis can be readily utilized to monitor anatoxin-a for water quality control.     

Determination of N‐nitrosamines by automated dispersive liquid–liquid microextraction integrated with gas chromatography and mass spectrometry

An automated dispersive liquid–liquid microextraction integrated with gas chromatography and mass spectrometric procedure was developed for the determination of three N‐nitrosamines (N‐nitroso‐di‐n‐propylamine, N‐nitrosopiperidine, and N‐nitroso di‐n‐butylamine) in water samples. Response surface methodology was employed to optimize relevant extraction parameters including extraction time, dispersive solvent volume, water sample pH, sodium chloride concentration, and agitation (stirring) speed. The optimal dispersive liquid–liquid microextraction conditions were 28 min of extraction time, 33 μL of methanol as dispersive solvent, 722 rotations per minute of agitation speed, 23% w/v sodium chloride concentration, and pH of 10.5. Under these conditions, good linearity for the analytes in the range from 0.1 to 100 μg/L with coefficients of determination (r²) from 0.988 to 0.998 were obtained. The limits of detection based on a signal‐to‐noise ratio of 3 were between 5.7 and 124 ng/L with corresponding relative standard deviations from 3.4 to 5.9% (n = 4). The relative recoveries of N‐nitroso‐di‐n‐propylamine, N‐nitrosopiperidine, and N‐nitroso di‐n‐butylamine from spiked groundwater and tap water samples at concentrations of 2 μg/L of each analyte (mean ± standard deviation, n = 3) were (93.9 ± 8.7), (90.6 ± 10.7), and (103.7 ± 8.0)%, respectively. The method was applied to determine the N‐nitrosamines in water samples of different complexities, such as tap water, and groundwater, before and after treatment, in a local water treatment plant.     

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%.     

Derivatization coupled to headspace programmed‐temperature vaporizer gas chromatography with mass spectrometry for the determination of amino acids: Application to urine samples

A new method based on headspace programmed‐temperature vaporizer gas chromatography with mass spectrometry has been developed and validated for the determination of amino acids (alanine, sarcosine, ethylglycine, valine, leucine, and proline) in human urine samples. Derivatization with ethyl chloroformate was employed successfully to determine the amino acids. The derivatization reaction conditions as well as the variables of the headspace sampling were optimized. The existence of a matrix effect was checked and the analytical characteristics of the method were determined. The limits of detection were 0.15–2.89 mg/L, and the limits of quantification were 0.46–8.67 mg/L. The instrumental repeatability was 1.6–11.5%. The quantification of the amino acids in six urine samples from healthy subjects was performed with the method developed with the one‐point standard additions protocol, with norleucine as the internal standard.     

Determination of free formaldehyde in vaccines and biological samples using solid‐phase microextraction coupled to GC–MS

A headspace solid‐phase microextraction method coupled to GC–MS was successfully developed for the trace determination of formaldehyde in veterinary bacterial and human vaccines, and diphtheria–tetanus antigen. The formaldehyde was derivatized by means of the Hantzsch reaction prior to extraction and subsequent determination. Three different types of solid‐phase microextraction fibers, polar, and nonpolar poly(dimethylsiloxane) and polyethylene glycol were prepared by using a sol–gel technique. The effects of different parameters such as type of fiber coating, extraction time and temperature, desorption conditions, agitation rate, and salt effect were investigated. Under the optimized conditions, the detection limit of the method was 979 ng/L using the selected ion‐monitoring mode. The interday and intraday precisions of the developed method under the optimized conditions were below 13%, and the method shows linearity in the range of 1.75–800 μg/L with a correlation coefficient of 0.9963. The optimized method was applied to the determination of formaldehyde from some biological products. The results were satisfactory compared to the standard method.     

Determination of nine volatile N‐nitrosamines in tobacco and smokeless tobacco products by dispersive solid‐phase extraction with gas chromatography and tandem mass spectrometry

A method was developed for the determination of nine volatile N‐nitrosamines in tobacco and smokeless tobacco products. The targets are N‐nitrosodimethylamine, N‐nitrosopyrrolidine, N‐nitrosopiperidine, N‐nitrosomorpholine, N‐nitrosoethylmethylamine, N‐nitrosodiethylamine, N‐nitrosodipropylamine, N‐nitrosobuylmethylmine, and N‐nitrosodibutylamine. The samples were treated by dispersive solid‐phase extraction using 1 g of primary secondary amine and 0.5 g of carbon and then analyzed by gas chromatography with tandem mass spectrometry with an electron impact ion source. The recoveries for the targets ranged from 84 to 118%, with <16% relative standard deviations at three spiking levels of 0.5, 1.25, and 2.5 ng/g. The limits of detection ranged from 0.03 to 0.15 ng/g. With the use of the proposed method, we detected the presence of six nitrosamines in the range of 0.4–30.7 ng/g. The study demonstrated that the method could be used as a rapid, convenient, and high‐throughput method for N‐nitrosamines analysis in tobacco matrix.     

Application of solid‐phase microextraction with gas chromatography and mass spectrometry for the early detection of active moulds on historical woollen objects

The goal of this work was to determine the microbial volatile organic compounds emitted by moulds growing on wool in search of particular volatiles mentioned in the literature as indicators of active mould growth. The keratinolytically active fungi were inoculated on two types of media: (1) samples of wool placed on broths, and (2) on broths containing amino acids that are elements of the structure of keratin. All samples were prepared inside 20 mL vials (closed system). In the first case (1) the broths did not contain any sources of organic carbon, nitrogen, or sulfur, i.e. wool was the only nutrient for the moulds. A third type of sample was historical wool prepared in a Petri dish without a broth and inoculated with a keratinolytically active mould (open system). The microbial volatiles emitted by moulds were sampled with the headspace solid‐phase microextraction method. Volatiles extracted on solid‐phase microextraction fibers were analyzed in a gas chromatography with mass spectrometry system. Qualitative and quantitative analyses of chromatograms were carried out in search of indicators of metabolic activity. The results showed that there are three groups of volatiles that can be used for the detection of active forms of moulds on woollen objects.     

Determination of substituted benzenes in water samples by fiber-in-tube liquid phase microextraction coupled with gas chromatography

A method for determination of toluene, ethylbenzene, p-xylene, o-xylene, 1,3,5-trimethylbenzene and 1,2,4-trimethylbenzene in water samples was developed by a fiber-in-tube liquid phase microextraction technique (fiber-in-tube LPME) coupled with GC-flame ionization detector (FID). The method used a tube packed with polytetrafluoroethylene (PTFE) fibers as an extraction medium, improving the stableness of the solvent and the performance of extraction. Certain amounts of curled PTFE fibers were packed into a section of PTFE tube. Because the fibers were curled, they formed network structure in the tube. The fiber packed tube was firstly immersed into organic solvent to be filled with organic solvent and then was exposing to an aqueous solution to extract the target compounds. The extract was then retracted by a conventional GC microsyringe and analyzed by GC-FID. Extraction of the analytes in 8 ml aqueous solution for 15 min yielded enrichment factors of 224-361. The precision (R.S.D., n = 5) was 3.6-8.1% for peak area. The limit of detection (LOD, S/N = 3) for the six substituted benzenes were in the range of 0.3-5.0 μg l⁻¹.