Monitoring the emission of volatile organic compounds from flowers of Jasminum sambac using solid-phase micro-extraction fibers and gas chromatography with mass spectrometry detection

Solid-phase micro-extraction (SPME) was studied as a solvent free alternative method for the extraction and characterization of volatile compounds in intact and plucked flowers of Jasminum sambac at different day time intervals using gas chromatography (GC-FID) and gas chromatography-quadrupole mass spectrometry. The analytes identified included alcohols, esters, phenolic compounds, and terpenoids. The main constituents identified in the flower aroma using different fibers were cis-3-hexenyl acetate, (E)-beta-ocimene, linalool, benzyl acetate, and (E,E)-alpha-farnesene. The benzyl acetate proportion decreased from morning to afternoon and then increased in evening collections. PDMS fiber showed a high proportion of (E,E)-alpha-farnesene in jasmine floral aroma. Among other constituents identified, cis-3-hexenyl acetate, linalool, and benzyl acetate were major aroma contributors in plucked and living flowers extracts using PDMS/DVB, Carboxen/PDMS, and DVB/Carboxen/PDMS fibers. PDMS/DVB recorded the highest emission for benzyl acetate while the (E)-beta-ocimene proportion was highest in DVB/Carboxen/PDMS when compared with the rest. The highest linalool content, with increasing proportion from morning to noon, was found using mixed coating fibers. Almost negligible volatile adsorption was recorded for the polyacrylate fiber for intact flower aroma, whereas it was most effective for benzyl acetate, followed by indole under plucked conditions. Moreover, the highest amounts extracted, evaluated from the sum of peak areas, were achieved using Carboxen/PDMS, and DVB/Carboxen/PDMS. Introduction of a rapid, and solvent free SPME method for the analysis of multicomponent volatiles can be successfully employed to monitor the extraction and characterization of flower aroma constituents.     

Analysis of organic volatile flavor compounds in fermented stinky tofu using SPME with different fiber coatings

The organic volatile flavor compounds in fermented stinky tofu (FST) were studied using SPME-GC/MS. A total of 39 volatile compounds were identified, including nine esters, seven alcohols, five alkenes, four sulfides, three heterocycles, three carboxylic acids, three ketones, two aldehydes, one phenol, one amine and one ether. These compounds were determined by MS, and conformed by comparison of the retention times of the separated constituents with those of authentic samples and by comparison of retention indexes (RIs) of separated constituents with the RIs reported in the literature. The predominant volatile compound in FST was indole, followed by dimethyl trisulfide, phenol, dimethyl disulfide and dimethyl tetrasulfide. In order to find a better extraction time, the extraction times was optimized for each type of SPME fiber; the results show that the best extraction time for Carboxen/PDMS is 60 min, for PDMS/DVB 30 min, for DVB/CAR/PDMS 60 min and for PDMS 75 min. Of the four fibers used in this work, Carboxen/PDMS is found to be the most suitable to extract the organic volatile flavor compounds in fermented stinky tofu.     

Development of a sensitive methodology for the analysis of chlorobenzenes in air by combination of solid-phase extraction and headspace solid-phase microextraction

In this study, a combination of solid-phase extraction (SPE) and solid-phase microextraction (SPME) has been used to determine chlorobenzenes in air. Analytes were sampled by pumping a known volume of air through a porous polymer (Tenax TA). Then, the adsorbent was transferred into a glass vial and SPME was performed. The quantification was carried out using gas chromatography (GC)-electron-capture detection or GC-MS. Several SPME coatings (100 microm poly(dimethylsiloxane) (PDMS), 75 microm Carboxen (CAR)-PDMS, 65 microm PDMS-divinylbenzene (DVB), 65 microm PDMS-DVB and 85 microm polyacrylate (PA) were evaluated, obtaining the highest responses with Carbowax (CW)- PDMS for the most volatile chlorobenzenes, and with PDMS-DVB or CW-DVB fibers for the semivolatile compounds. To optimize some other factors that could affect the SPME step, a factorial design was used. Kinetic studies of the SPME process were also performed. Concerning the SPE step, breakthrough was studied, showing that 2.5 m3 of air could be processed without losses of the most volatile compounds. The performance of the method was evaluated. External calibration, which does not require the complete sampling process, demonstrated to be suitable, obtaining good linearity (R2 > 0.99) for all chlorobenzenes. Recovery studies were performed at two concentration levels (4 and 40 ng/m3), obtaining quantitative recoveries (>80%). Limits of detection at the sub ng/m3 were achieved for all the target compounds.     

Optimization of the SPME device design for field applications

Solid Phase Microextraction (SPME) is a powerful tool for field investigations. With the help of a portable gas chromatograph it can be used for fast analysis directly on-site, or it can be utilized for field sampling and then transported to the laboratory for instrumental analysis. In the latter case, it is important for the reliability of the results that losses of volatiles and contamination of the fiber during storage and transport are minimized. A number of dedicated devices, designed and built for SPME field sampling and storage, have been developed and tested. Sealing capacity of the prototypes was investigated by storing compounds ranging in volatility from methylene chloride to 1,3-dichlorobenzene on selected SPME fibers (100 μm PDMS, 65 μm PDMS/DVB and 75 μm Carboxen/PDMS) at different temperatures. Significant differences were noticed in storage capacity from coating to coating. A comparison between the field samplers optimized in this study and the field sampler commercially available from Supelco revealed advantages and limitations of each of the designs. A gas-tight valve syringe (50 μL SampleLock by Hamilton), modified in order to accommodate the SPME fiber, had the best storage capacity for very volatile compounds. With this device, over 80% of the initial amount of methylene chloride was retained by the 100 μm PDMS fiber after 24 h of refrigerated storage, which is a very good result considering that the PDMS coating is characterized by very low storage capacity for volatiles. Field sampling investigations with the SPME prototypes confirmed the usefulness of these devices for field analysis. Received: 9 November 1998 / Accepted: 15 January 1999     

Optimization of the SPME device design for field applications

Solid Phase Microextraction (SPME) is a powerful tool for field investigations. With the help of a portable gas chromatograph it can be used for fast analysis directly on-site, or it can be utilized for field sampling and then transported to the laboratory for instrumental analysis. In the latter case, it is important for the reliability of the results that losses of volatiles and contamination of the fiber during storage and transport are minimized. A number of dedicated devices, designed and built for SPME field sampling and storage, have been developed and tested. Sealing capacity of the prototypes was investigated by storing compounds ranging in volatility from methylene chloride to 1,3-dichlorobenzene on selected SPME fibers (100 μm PDMS, 65 μm PDMS/DVB and 75 μm Carboxen/PDMS) at different temperatures. Significant differences were noticed in storage capacity from coating to coating. A comparison between the field samplers optimized in this study and the field sampler commercially available from Supelco revealed advantages and limitations of each of the designs. A gas-tight valve syringe (50 μL SampleLock by Hamilton), modified in order to accommodate the SPME fiber, had the best storage capacity for very volatile compounds. With this device, over 80% of the initial amount of methylene chloride was retained by the 100 μm PDMS fiber after 24 h of refrigerated storage, which is a very good result considering that the PDMS coating is characterized by very low storage capacity for volatiles. Field sampling investigations with the SPME prototypes confirmed the usefulness of these devices for field analysis. Received: 9 November 1998 / Accepted: 15 January 1999     

Triptycene‐Roofed Quinoxaline Cavitands for the Supramolecular Detection of BTEX in Air

Two novel triptycene quinoxaline cavitands ( DiTriptyQxCav and MonoTriptyQxCav ) have been designed, synthesized, and applied in the supramolecular detection of benzene, toluene, ethylbenzene, and xylenes (BTEX) in air. The complexation properties of the two cavitands towards aromatics in the solid state are strengthened by the presence of the triptycene moieties at the upper rim of the tetraquinoxaline walls, promoting the confinement of the aromatic hydrocarbons within the cavity. The two cavitands were used as fiber coatings for solid‐phase microextraction (SPME) BTEX monitoring in air. The best performances in terms of enrichment factors, selectivity, and LOD (limit of detection) values were obtained by using the DiTriptyQxCav coating. The corresponding SPME fiber was successfully tested under real urban monitoring conditions, outperforming the commercial divinylbenzene–Carboxen–polydimethylsiloxane (DVB–CAR–PDMS) fiber in BTEX adsorption.     

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.     

Needle trap micro-extraction for VOC analysis: Effects of packing materials and desorption parameters

Combining advantages of SPE and SPME needle trap devices (NTD) represent promising new tools for a robust and reproducible sample preparation. This study was intended to investigate the effect of different packing materials on efficacy and reproducibility of VOC analysis by means of needle trap micro extraction (NTME). NTDs with a side hole design and containing different combinations of PDMS, DVB and Carbopack X and Carboxen 1000 and NTDs containing a single layer organic polymer of methacrylic acid and ethylene glycol dimethacrylate were investigated with respect to reproducibility, LODs and LOQs, carry over and storage. NTDs were loaded with VOC standard gas mixtures containing saturated and unsaturated hydrocarbons, oxygenated and aromatic compounds. Volatile substances were thermally desorbed from the NTDs using fast expansive flow technique and separated, identified and quantified by means of GC–MS. Optimal desorption temperatures between 200 and 290 °C could be identified for the different types of NTDs with respect to desorption efficiency and variation. Carry over was below 6% for polymer packed needles and up to 67% in PDMS/Carboxen 1000 NTDs. Intra and inter needle variation was best for polymer NTDs and consistently below 9% for this type of NTD. LODs and LOQs were in the range of some ng/L. Sensitivity of the method could be improved by increasing sample volume. NTDs packed with a copolymer of methacrylic acid and ethylene glycol dimethacrylate were universally applicable for sample preparation in VOC analysis. If aromatic compounds were to be determined DVB/Carboxen 1000 and DVB/Carbopack X/Carboxen 1000 devices could be considered as an alternative. PDMS/Carbopack X/Carboxen 1000 NTDs may represent a good alternative for the analysis of hydrocarbons and aldehydes. NTME represents a powerful tool for different application areas, from environmental monitoring to breath analysis.     

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%).     

SPME Analysis of Potential Attractants for Palm Weevils

Abstract

Solid-phase microextraction was applied for the analysis of a mixture of potential attractants for palm weevils, constituted by seven organic compounds. Various fibers, coated with different sorbent phases, were used in this study and the best results were obtained with the polydimethylsiloxane (PDMS)/divinylbenzene (DVB) and the Carboxen/PDMS fibers. A waiting time of 5 min before sampling was adequate for sample homogenisation and a sampling time of 30 min was used to obtain good extraction efficiencies. A complete desorption of the analytes into the injection port of the gas chromatograph was achieved with an injection time of 1 min. The detection limit of the method ranged from 0.29 to 156 ng/ml for the different components of the mixture, with a lower detection limit for the compounds with higher affinity for the fiber coating. This method was used in the analysis of volatiles released from a diffuser filled with the attractant mixture.     

Determination of haloanisoles in paper samples for food packaging by solid-phase microextraction and gas chromatography

A method was developed for the determination of trichloroanisole, tribromoanisole and pentachloroanisol by solid-phase microextraction and gas chromatography in paper samples (Kraft liner, Test liner and Miolo). Four commercial SPME fibers were evaluated: Polydimethylsiloxane (PDMS), Polyacrylate (PA), Carbowax/Divinylbenzene (CW/DVB) and Divinylbenzene/Carboxen/Polydimethylsiloxane (DVB/CAR/PDMS). DVB/CAR/PDMS gave the best results and was therefore selected. Other variables involved in the extraction procedure were studied and optimized, such as: sample volume, salting-out effect, temperature and extraction time, effect of organic solvent and previous sample preparation. Optimum conditions were obtained using 20 mL of sample with 5 mol L⁻¹ NaCl in a 40 mL vial, extraction temperature of 70 °C and sonication and extraction time of 30 and 40 min, respectively. Detection limits ranged from 0.43 to 1.32 ng g⁻¹ for all analytes. Recoveries between 70 and 100% were obtained and relative standard deviation was below 10% for all compounds.     

Flavour analysis of Greek white wine by solid-phase microextraction-capillary gas chromatography-mass spectrometry

Solid-phase microextraction (SPME) was optimised for the qualitative determination of the volatile flavour compounds responsible for the aroma of Greek Boutari wine. Several factors influencing the equilibrium of the aroma compounds between the sample and the SPME fiber were taken into account, including the extraction time, the extraction temperature, the sampling mode (headspace and direct immersion or liquid SPME), and the presence of salt. Four different SPME fibers were used in this study. namely poly(dimethylsiloxane) (PDMS), poly(acrylate), carbowax-divinylbenzene and divinylbenzene-carboxen on poly(dimethylsiloxane). The best results were obtained using the PDMS fiber during headspace extraction at 25 degrees C for 30 min after saturating the samples with salt. The optimised SPME method was then applied to investigate the qualitative aroma composition of three other Greek wines, namely Zitsa, Limnos and Filoni.     

Preparation and application of poly(dimethylsiloxane)/beta-cyclodextrin solid-phase microextraction fibers

A novel poly(dimethylsiloxane)/beta-cyclodextrin (PDMS/beta-CD) coating was prepared for solid-phase microextraction (SPME). The PDMS/beta-CD coating proved to have a porous structure, providing high surface areas and allowing for high extraction efficiency. The coating had a high thermal stability (340 degrees C) and a long lifetime due to its chemical binding to the fiber surface. Polar phenols and amines were used to evaluate the character of the coating fiber by headspace (HS) extraction and thermal desorption, followed by GC-FID analysis. Parameters that affected the extraction process were investigated; these include extraction time and temperature, desorption time, pH, and ionic strength of the solution. For phenols, the range of linearity of the method was 4-500 microg/L and the LOD was 1.3-2.1 microg/L. For amines, the range of linearity was 1-1000 microg/L and the LOD was 1.2-2.8 microg/L. The presence of beta-CD not only increases the thermal stability of the fiber coating, but also enhances its selectivity. Compared with commercially available SPME fibers, the new phases show better selectivity and sensitivity towards polar compounds.     

Comparative study of the whisky aroma profile based on headspace solid phase microextraction using different fibre coatings

A dynamic headspace solid-phase microextraction (HS-SPME) and gas chromatography coupled to ion trap mass spectrometry (GC-(IT)MS) method was developed and applied for the qualitative determination of the volatile compounds present in commercial whisky samples which alcoholic content was previously adjusted to 13% (v/v). Headspace SPME experimental conditions, such as fibre coating, extraction temperature and extraction time, were optimized in order to improve the extraction process. Five different SPME fibres were used in this study, namely, poly(dimethylsiloxane) (PDMS), poly(acrylate) (PA), Carboxen-poly(dimethylsiloxane) (CAR/PDMS), Carbowax-divinylbenzene (CW/DVB) and Carboxen-poly(dimethylsiloxane)-divinylbenzene (CAR/PDMS/DVB). The best results were obtained using a 75 microm CAR/PDMS fibre during headspace extraction at 40 degrees C with stirring at 750 rpm for 60 min, after saturating the samples with salt. The optimised methodology was then applied to investigate the volatile composition profile of three Scotch whisky samples--Black Label, Ballantines and Highland Clan. Approximately seventy volatile compounds were identified in the these samples, pertaining at several chemical groups, mainly fatty acids ethyl esters, higher alcohols, fatty acids, carbonyl compounds, monoterpenols, C13 norisoprenoids and some volatile phenols. The ethyl esters form an essential group of aroma components in whisky, to which they confer a pleasant aroma, with "fruity" odours. Qualitatively, the isoamyl acetate, with "banana" aroma, was the most interesting. Quantitatively, significant components are ethyl esters of caprilic, capric and lauric acids. The highest concentration of fatty acids, were observed for caprilic and capric acids. From the higher alcohols the fusel oils (3-methylbutan-1-ol and 2.phenyletanol) are the most important ones.     

葫芦脲用作固相微萃取涂层新材料

本文对葫芦脲(CB)作为一种新型固相微萃取(SPME)涂层材料进行了研究并用于中药白豆蔻的气相色谱分析测定.本文采用的CB SPME涂层制备方法简便、快速,并具有良好的热稳定性和重复性.CB[6]SPME萃取得到的主要成分与水蒸气蒸馏（SD）法基本一致,并且CB[6]SPME对色谱后流出的目标成分的相对峰面积比明显高于SD法和商品SPME萃取材料PDMS/CAR和PDMS/DVB,这可能是由于葫芦脲的特殊分子结构及其与组分分子间选择性作用所致.葫芦脲作为一种新型SPME涂层材料具有很大的研究潜力和应用前景.     

顶空固相微萃取-气相色谱-质谱法测定小米黄酒风味成分

为全面了解小米黄酒风味成分的构成和气味特征,优化了85μm聚丙烯酸酯(PA)、100μm聚二甲基硅氧烷(PDMS)、75μm碳分子筛(CAR)/PDMS、50/30μm二乙烯基苯(DVB)/CAR/PDMS萃取头提取小米黄酒风味成分的条件,采用顶空固相微萃取(headspace solid phase microextraction,HS-SPME)-气相色谱-质谱法(GC-MS)对风味成分进行定性、定量分析,并计算气味活性值(odor active value,OAV),同时利用OAV分析风味成分的气味特征和气味强度。结果显示:不同萃取头的最优萃取条件为样品量8 mL、萃取时间40 min、萃取温度60℃、NaCl添加量1.5 g。小米黄酒风味成分由醇、酯、含苯化合物、烃、酸、醛、酮、烯、酚和杂环类化合物构成,醇为主要风味成分。通过OAV确定了苯乙醇、苯乙烯、2-甲基萘、1-甲基萘、苯甲醛、苯乙醛、2-甲氧基-苯酚为小米黄酒气味特征成分,苯基乙醇、苯乙醛对气味贡献最大。PA和PDMS萃取头分别对极性和非极性化合物具有较好的吸附效果,CAR/PDMS和DVB/CAR/PDMS萃取头对中等极性化合物具有较好的吸附效果。该研究全面了解了小米黄酒风味成分的构成,为其产品开发及品质控制提供理论了依据。     

Development and Evaluation of a New Fluorinated Double-Wall Carbon Nanotube HPLC Stationary Phase

A novel column based on silica-containing immobilized fluorinated double-wall carbon nanotubes (F-DWCNTs) was developed. This F-DWCNT stationary phase was synthesized to combine the analytical performance of carbon nanotubes and the fluorine-based unique selectivity for polar compounds. First, the chromatographic support was coated with DWCNTs in a noncovalent way to preserve the sp² internal nanotube structure. Second, the DWCNT silica particles were functionalized with fluorine atoms via a solution of Br₂ and BrF₃ at room temperature. This F-DWCNT stationary phase was applied for a variety of separations. The solute retention behaviour was particularly studied under isocratic conditions with a high fraction of ACN in the ACN/water (v/v) mobile phase. The retention factors of the solute molecule do not depend linearly on the ACN fraction, but follow a quadratic relationship. This fluorinated stationary phase separated compounds based upon a combination of hydrophobic and polar selective stationary phase interactions. This F-DWCNT appeared to work best when fluorinated or halogenated compounds were encountered. They have longer retention time, better selectivity and work well with high fraction of organic modifiers. This novel stationary phase could thus be a good choice for LC–MS experiments.     

Determination of phthalates in water using fiber introduction mass spectrometry

Fiber introduction mass spectrometry (FIMS)-a direct coupling of SPME and MS-using selective ion monitoring (SIM) was used to detect and quantify dimethylphthalate (DMP), diethylphthalate (DEP) and dipropylphthalate (DPP) in mineral water. In FIMS, a chromatographic silicone septum is the only barrier between ambient and the high-vacuum mass spectrometer, permitting direct introduction of the SPME fiber into the ionization region of the equipment. After their thermal desorption and ionization and dissociation, the extracted phthalates are detected and quantitated by MS. Three types of SPME fibers were screened for best analyte sorption/desorption behaviors: 100 microm polydimethylsiloxane (PDMS), 65 microm polydimethylsiloxane/divinylbenzene (PDMS/DVB) and 65 microm Carbowax/divinylbenzene (CW/DVB). The PDMS/DVB and CW/DVB fibers were then evaluated for precision, and quantitative figures of merit were assessed for extractions using the PDMS/DVB fiber, which displayed the best overall performance. FIMS with the PDMS/DVB fiber allows simple extraction and MS detection and quantitation of DMP in water with good linearity and precision, and at concentrations as low as 3.6 microg L(-1). The LD and LQ of FIMS are below the maximum phthalate concentration allowed by the USEPA for drinking water (6 microg L(-1)).     

Glass nebulizer interface for capillary electrophoresis-Fourier transform infrared spectrometry

Despite the continuing development of SPME (solid-phase microextraction) fibre coatings, their selection presents some difficulties for analysts in choosing the appropriate fibre for a certain application. There are two distinct types of SPME coatings available commercially. The most widely used are poly(dimethylsiloxane) (PDMS) and poly(acrylate) (PA). Supelco has developed new mixed phases consisting of porous polymer particles, either poly(divinylbenzene) (DVB) or Carboxen suspended in a matrix of PDMS or Carbowax for extracting analytes via adsorption. In addition to the nature of the extracting phase, the thickness of the polymeric film must be taken into account and, surprisingly, the construction of the fibres when apparently they bear the same coating, as it is the case of the three PDMS-DVB fibres available. Other fibre structure properties not well explored were identified and must be taken into consideration. To elucidate their extraction efficiency, three PDMS-DVB fibres, namely 60 microm for HPLC use, 65 microm for GC use and 65 microm StableFlex for GC use, were compared with regard to the extraction of 36 compounds included in four pesticide groups. The first was particularly suited for the extraction of organophosphorus pesticides and triazines whereas the StableFlex exhibited advantages in the analysis of organochlorine pesticides and pyrethroids. An explanation for the extraction differences is suggested based on the different structure of the fibres. Detection limits in the range of 1-10 ng/l for organochlorine pesticides, 1-30 ng/l for organophosphorus pesticides, 8-50 ng/l for triazines and 10-20 ng/l for pyrethroids were attained in a method using the 60 microm PDMS-DVB fibre. The fibre maintains its performance at well above 100 extractions with between-day precision below 10%.     

Preparation and Characterization of Prometryn Molecularly Imprinted Solid‐Phase Microextraction Fibers

Abstract

A novel reproducible solid‐phase microextraction (SPME) coating was prepared on the surface of silanized silica fibers by molecularly imprinted polymerization using prometryn as template molecule. The structure and extraction performance of molecularly imprinted polymer (MIP) coating was studied with the scanning electron microscope and high performance liquid chromatography (HPLC). Specific selectivity was found with the prometryn MIP‐coated fiber to prometry and its structural analogues such as atrazine, simetryn, terbutylazin, ametryn, propazine and terbutryn. In contrast, these triazines could not be selectively extracted by the non‐imprinted polymer fiber or commercial polydimethylsiloxane (PDMS), polydimethylsiloxane/divinylbenzene (PDMS/DVB), polyacrylate (PA) fibers.