Conventional Solid-phase Microextraction Research Articles

Solid-phase microextraction Arrow combined with comprehensive two-dimensional gas chromatography-mass spectrometry for the elucidation of the volatile composition of honey samples.

In this work, a solid-phase microextraction (SPME) Arrow method combined with comprehensive two-dimensional gas chromatography-mass spectrometry (GC × GC-MS) was developed for the elucidation of the volatile composition of honey samples. The sample preparation protocol was optimized to ensure high extraction efficiency of the volatile organic compounds (VOCs) which are directly associated with the organoleptic properties of honey and its acceptance by the consumers. Following its optimization, SPME Arrow was compared to conventional SPME in terms of sensitivity, precision, and number of extracted VOCs. The utilization of SPME Arrow fibers enabled the determination of 203, 147, and 149 compounds in honeydew honey, flower honey, and pine honey, respectively, while a significantly lower number of compounds (124, 94, and 111 for honeydew honey, flower honey, and pine honey, respectively) was determined using conventional SPME. At the same time, the utilization of SPME Arrow resulted in enhanced sensitivity and precision. All things considered, SPME Arrow and GC × GC-MS can be considered as highly suitable for the elucidation of the volatile composition of complex food samples resulting in high sensitivity and separation efficiency.

Exploring the volatile profile of whiskey samples using solid-phase microextraction Arrow and comprehensive two-dimensional gas chromatography-mass spectrometry

We present a novel sample preparation method for the extraction and preconcentration of volatile organic compounds from whiskey samples prior to their determination by comprehensive two-dimensional gas chromatography (GC × GC) coupled to mass spectrometry (MS). Sample preparation of the volatile compounds, important for the organoleptic characteristics of different whiskeys and their acceptance and liking by the consumers, is based on the use of the solid-phase microextraction (SPME) Arrow. After optimization, the proposed method was compared with conventional SPME regarding the analysis of different types of whiskey (i.e., Irish whiskey, single malt Scotch whiskey and blended Scotch whiskey) and was shown to exhibit an up to a factor of six higher sensitivity and better repeatability by a factor of up to five, depending on the compound class. A total of 167 volatile organic compounds, including terpenes, alcohols, esters, carboxylic acids, ketones, were tentatively-identified using the SPME Arrow technique, while a significantly lower number of compounds (126) were determined by means of conventional SPME. SPME Arrow combined with GC × GC-MS was demonstrated to be a powerful analytical tool for the exploration of the volatile profile of complex samples, allowing to identify differences in important flavour compounds for the three different types of whiskey investigated.

An Improvement of SPME-Based Sampling Technique to Collect Volatile Organic Compounds from Quercus ilex at the Environmental Level.

Biogenic Volatile Organic Compounds (BVOCs) include many chemical compounds emitted by plants into the atmosphere. These compounds have a great effect on biosphere–atmosphere interactions and may affect the concentration of atmospheric pollutants, with further consequences on human health and forest ecosystems. Novel methods to measure and determine BVOCs in the atmosphere are of compelling importance considering the ongoing climate changes. In this study, we developed a fast and easy-to-handle analytical methodology to sample these compounds in field experiments using solid-phase microextraction (SPME) fibers at the atmospheric level. An improvement of BVOCs adsorption from SPME fibers was obtained by coupling the fibers with fans to create a dynamic sampling system. This innovative technique was tested sampling Q. ilex BVOCs in field conditions in comparison with the conventional static SPME sampling technique. The results showed a great potential of this dynamic sampling system to collect BVOCs at the atmosphere level, improving the efficiency and sensitivity of SPME fibers. Indeed, our novel device was able to reduce the sampling time, increase the amount of BVOCs collected through the fibers and add information regarding the emissions of these compounds at the environmental level.

A thin‐layer solid‐phase extraction–liquid film elution technique used for the enrichment of polycyclic aromatic hydrocarbons in water

In this article, we propose a novel microsolid-phase extraction and elution technique, which we called the thin-layer solid-phase extraction-liquid film elution technique. The thin-layer solid-phase extraction phase is an octadecylsilylated sol gel- coated porous silica thin film prepared on the outer wall of a test tube, which has a larger surface area for the extraction of the target compounds compared to a conventional solid-phase microextraction phase. After optimization of the extraction procedure for five types of polycyclic aromatic hydrocarbons, the liquid film elution technique was investigated. Liquid film elution is an elution technique wherein the compounds extracted into the thin-layer solid-phase extraction phase are eluted using a small volume of solvent film formed around the extraction phase. The results show that the elution can be carried out using 150 μL of eluent. Enrichment factors between 20 and 34 were obtained for polycyclic aromatic hydrocarbons containing more than four aromatic rings in 10mL aliquots of aqueous samples. Finally, recoveries of 85-112% were obtained for polycyclic aromatic hydrocarbons containing more than four aromatic rings from spiked natural water samples using the thin-layer solid-phase extraction-liquid film elution technique.

Development and comparison of direct immersion solid phase micro extraction Arrow-GC-MS for the determination of selected pesticides in water

Pesticides are compounds which can affect human, environmental and aquatic system health. Therefore, the detection and determination of these compounds at trace level concentrations is of great importance. In this study selected pesticides out of four classes were investigated as target analytes: Dichlorovos as an insecticide, terbutryn as herbicide, cybutryne from the group of biocides and quinoxyfen as an example of fungicides. A direct immersion solid phase micro extraction (SPME) Arrow-GC–MS method was developed and validated for fully automated microextraction of the target compounds from aqueous samples. In this regard, the most important experimental parameters of the extraction: Extraction time, extraction temperature, pH, ionic strength of the sample and the Arrow type, were studied and optimized. In addition, the developed method was compared with the conventional SPME, regarding sensitivity, relative recovery and precision. The limit of detection values of SPME Arrow were between 0.68 and 544 ng L-1 for dichlorvos and quioxyfen, respectively, and significantly less than similar values obtained from conventional SPME (4.63 and 4400 ng L-1 for the same compounds). For all investigated pesticides, recovery rates ranged between 90 and 116% for the Arrow as well as 85 and 107% for the classical SPME fiber. Relative standard deviations (RSD %) were 4.3–7.8 and 3.5–11.8 for the Arrow and classic SPME, respectively. Also, coefficient of determination (R2) range was within the range of 0.993–0.999 for SPME Arrow and 0.990–0.996 for classic SPME.

Solid-Phase Microextraction Arrow for the Sampling of Volatile Organic Compounds in Milk Samples

A novel sample preparation method based on the use of the Arrow solid-phase microextraction device was used to extract and preconcentrate volatile organic compounds (VOCs) from milk samples prior to their determination by gas chromatography–mass spectrometry (GC-MS). The experimental parameters of the solid-phase microextraction (SPME) Arrow method were evaluated in terms of fiber type, sample volume, extraction temperature, extraction time, stirring rate and salt addition. Under the optimum extraction conditions, the SPME Arrow was compared with conventional SPME fibers to evaluate the effectiveness of the SPME Arrow method. Evaluation of the conventional SPME procedure was also performed under optimized conditions, for appropriate method comparison. Due to the larger sorption phase volume of SPME Arrow, a higher sensitivity and reproducibility were observed for the determined chromatographic peaks in comparison with conventional SPME fibers. The use of Carbon wide range (WR) SPME Arrow/polydimethylsiloxane (CAR/PDMS) SPME Arrow fibers leads to a compound-dependent improvement of a factor of 4–5x over the classical SPME setup. Moreover, the relative standard deviation (RSD) of the total volatiles for a conventional SPME procedure was 12.5%, while for SPME Arrow it was 6.2%. Finally, the novel method was successfully employed for the analysis of commercially available milk samples. The findings of this study indicate that SPME Arrow can be effectively used for the determination of volatile organic compounds in complex food matrixes.

Introduction of a biowaste/graphene oxide nanocomposite as a coating for a metal alloy based SPME fiber: Application to screening of polycyclic aromatic hydrocarbons

The present study introduces a high efficiency metal alloy-based solid-phase microextraction (SPME) fiber coated with a green biowaste nanocomposite of chicken feet yellow membrane mixed with graphene oxide (CFYM/GO). An Al/Cr commercial heating element (aluchrom, AC) has been selected as the fiber substrate and designed as coiled form (CAC-SPME) to enhance its extraction and pre-concentration capacity. The fabricated fiber, CAC-SPME/CFYM/GO, has been employed for the extraction and pre-concentration of some commonly seen PAHs in different standard/real samples prior to their high performance liquid chromatography- ultraviolet (HPLC-UV) analyzing. The synthesized materials and the fibers surface were characterized by field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, Fourier-transform infrared spectroscopy analysis and Brunauer-Emmett-Teller surface area analysis. Under the optimized experimental conditions, low detection limits (LOD, 0.039–0.30 µg L–1), wide linear ranges (LR, 0.13–643 µg L–1) and good relative recoveries (RR, 76.20–105.60%) were achieved for all the target analytes. The materials applied to prepare this fiber were low-priced and accessible and also eliminated the need for expensive coating substances. In addition, using of the AC alloy substrate was increased the fiber physicochemical resistance and solved the breakage drawback of the conventional SPME fibers. Moreover, simple fabrication, high rigidity, long service life and high extraction capacity were some of the other advantages of the suggested fiber. Therefore, the proposed method can be utilized successfully for the routine analysis of PAHs in different matrixes.

Thermal desorption sampling-gas chromatography-tandem mass spectrometry with a carbonyl-iron powder composite silica monolithic column for enrichment and determination of pyrethroid pesticide residues in tea samples

Long-term exposure to pyrethroid insecticides is detrimental to the nervous system, reproductive system, and immune system in humans. Therefore, enrichment detection of pyrethroid pesticides is imperative. In this study, a novel carbonyl-iron powder composite silica monolithic column was first prepared for the enrichment of pyrethroid pesticide residues in tea samples. Then, the target analytes were thermally desorbed and online-injected into a gas chromatography-tandem mass spectrometry (GC-MS/MS) system. In the present method, hydroxy-terminated polydimethylsiloxane (PDMS) was covalently bonded to the surface of the SiO2 network and subsequently bonded with the carbonyl-iron powder. After the target analytes were adsorbed and concentrated in the PDMS spots, high-frequency induction heating was used for GC-MS/MS sampling. Under the optimal conditions, the detection limits of the pyrethroid pesticide residues were 3.8 to 7.5 μg/kg, and the relative standard deviation was 3.2% to 6.8% (n=6). The extraction recovery ranged from 97.7% to 110.5%, and the correlation coefficient was ≥ 0.9960. In addition, the enrichment factor could reach 1000 times. PDMS materials show excellent adsorption properties for non-polar solutes. In our experiment, carbonyl iron powder-bonded monolithic columns were prepared on the basis of stir bar sorptive extraction (SBSE). Carbonyl iron powder magnetic particles were evenly implanted into the inorganic-organic hybrid cassia material for realizing rapid and uniform desorption upon electromagnetic induction heating. Under the premise of perfectly integrating the technical advantages of SBSE and solid-phase microextraction (SPME), the electromagnetic induction characteristics of carbonyl iron powder can be exploited for thermal desorption and directly combined with GC-MS to facilitate online analysis and solvent-free elution. Compared with the conventional SPME method, the proposed method has the advantages of high enrichment factor, large adsorption capacity of the column, reusability, high degree of automation, and good universality. This method has high significance for sample preparation and for the extraction of pesticide residues in complex matrices.

A 96-Monolithic inorganic hollow fiber array as a new geometry for high throughput solid-phase microextraction of doxorubicin in water and human urine samples coupled with liquid chromatography-tandem mass spectrometry.

Innovations in extraction phases, extraction modes and hyphenated instrument configurations, are the most important issues to address for progress in the solid phase microextraction (SPME) methodology. In this regard, we have embarked on the development of a novel biocompatible 96-monolithic inorganic hollow fiber (96-MIHF) array as a new configuration for high-throughput SPME on a 96-well plate system. An arrangement of highly ordered 96 titania/Hydroxyapatite (TiO2/HAP) nanocomposite hollow fibers and corresponding stainless-steel needles on a Teflon plate holder were used as the extraction module. The inorganic hollow fibers were prepared via a rapid and reproducible template approach (Polypropylene hollow fiber) in combination with a sol-gel method in the presence of polyvinyl alcohol (PVA), as a network maker. The hollow fiber-shape sorbents were obtained with excellent precision by weight (RSD%=4.98, n=10) and length (RSD%=1.08, n=10) criteria. The proposed design can overcome a number of geometrically dependent drawbacks of conventional high-throughput SPME methods, mainly the ones related to sorbent amount and surface area due to possessing inner/outer surfaces without additional internal supports. The SPME platform, for the first time, was successfully applied for the extraction and preconcentration of doxorubicin from urine and water media without requiring sample preparation and free from significant matrix effect. The extracted analyte was analyzed by liquid chromatography-ion trap tandem mass spectrometry (LC-MS/MS). Highly satisfactory analytical figures of merit were obtained under optimized conditions. The limit of detection (LOD), limit of quantification (LOQ) and linearity of determination were 0.1ngmL-1, 0.25ngmL-1 and 0.25 to 4000ngmL-1, respectively. The interday, intraday and inter sorbent precisions for three concentration levels ranged from 2.01 to 8.09 % (n=3), 1.02 to 8.65 % (n=5) and 0.99 to 1.02% (n=15), respectively. The mean intra-well RSD value for 96 individual wells in 96-MIHF-SPME-LC-MS/MS (n=3) at the medium concentration level was 7.81%.

Design and optimization of the VA-TV-SPME method for ultrasensitive determination of the PAHs in polluted water

This paper describes how a novel and reliable alternative approach was developed for conventional solid-phase microextraction (SPME) sampling by total-vaporization of a sample under vacuum conditions. SPME sampling consists two stages of the equilibrium process, which take place between the sample/headspace and the headspace/fiber coating. In the total-vaporization SPME (TV-SPME) strategy, the first stage is omitted and analytes are directly partitioned between the headspace and fiber coating. In this research, the TV-SPME strategy was implemented by the extraction of PAHs from aqueous media, using a polydimethylsiloxane (PDMS) coated SPME fiber. The most important variables were investigated and optimized. Optimal conditions were obtained at an extraction temperature of 55 °C, a vaporization time of 25 min, and a sample volume of 100 μL. To achieve higher sensitivities in shorter times, the TV-SPME setup was coupled with the VA-SPME system, which resulted in a much lower extraction temperature and time, in comparison with the conventional TV-SPME method. Under optimal experimental conditions, the calibration curves were linear across the area of 0.015–2 μg mL−1 (R2 > 0.996). The limits of detection (LODs) were obtained in the range of 0.3–5 ng mL−1, and the relative standard deviations (RSDs, n = 6) were 6.1–7.5%. The developed vacuum-assisted total-vaporization SPME (VA-TV-SPME) technique, was coupled with GC-FID and successfully utilized for the determination of polycyclic aromatic hydrocarbons (PAHs) in river water samples. The data obtained was statistically in accordance with that achieved employing a validated approved method.

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 60min). The optimal solid-phase microextraction Arrow conditions were as follows: type of fiber=polyacrylate, extraction time=60min, 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.

Analyzing volatiles in brown rice vinegar by headspace solid-phase microextraction (SPME)–Arrow: Optimizing the extraction conditions and comparisons with conventional SPME

ABSTRACTThe ability to readily determine the composition of brown rice vinegar is important for quality assurance purposes. To that end, solid–phase microextraction (SPME)–Arrow method was optimized for the determination of volatile organic compounds (VOCs) from brown rice vinegar. Compared to traditional SPME fibers, SPME–Arrow has a larger sorbent-phase volume and is more durable. The SPME–Arrow conditions, including coating material, extraction temperature, extraction time, and NaCl concentration, were examined, which led to optimum extraction conditions that include: carboxen/polydimethylsiloxane (CAR/PDMS) fiber, 50°C, 30 min of SPME–Arrow, and 0% NaCl (i.e., no added NaCl). The developed method was compared to an optimized method based on conventional SPME. Twelve major VOCs, including acetates, alcohols, aldehydes, acids, and furan derivatives, were extracted by SPME–Arrow, while only seven VOCs were extracted using the traditional SPME. Moreover, SPME–Arrow extracted more 1.3–2 times more VOCs than SPME. Hence, the CAR/PDMS SPME–Arrow fiber is suitable for acquiring VOC profiles from brown rice vinegar.

NEW METHYLTRIMETHOXYSILANE-(3-MERCAPTOPROPYL)-TRIMETHOXYSILANE COATED HOLLOW FIBER-SOLID PHASE MICROEXTRACTION FOR HEXANAL AND HEPTANAL ANALYSIS

Determination of volatile organic compounds (VOCs) in various matrices is often accomplished using solid phase microextraction (SPME) as a superior mode of extraction. Alternatively, another configuration of solid phase microextraction (SPME) namely hollow fiber-solid phase microextraction (HF-SPME) is a great approach to redress some limitations of the ordinary SPME fibers including fiber breakage, coating stripping and sample carry over. The HF-SPME technique highlights the use of hollow polypropylene (PP) membrane to hold and protect the adsorbent inside its lumen. Unlike the conventional SPME, the inexpensive HF device can be disposed after single use. Introducing extracting phase via sol-gel technology has gained great interest owing to its simple preparation method and promising way to obtain materials with good characteristics. In the present work, a new hybrid silica material based on methyltrimethoxysilane-(3-mercaptopropyl)trimethoxysilane (MTMOS-MPTMOS) was introduced as a new extractant of HF-SPME and the effectiveness of the proposed method was tested for analysis of hexanal and heptanal as the target VOC analytes. Preparation of the HF-SPME MTMOS-MPTMOS was simple in which the hybrid material was synthesized via sol-gel method and was self-polymerized in small segments of HF. Parameters affecting the efficiency of the HF-SPME MTMOS-MPTMOS in extracting both aldehydes were thoroughly investigated and analyzed by gas chromatography-flame ionization detection (GC-FID). It was found that the highest efficiency was achieved as the extraction was conducted in 30 min at a stirring rate of 1000 rpm in a 10 mL of sample solution whereby the back-extraction was performed via vortex for 3 min using 100 µL methanol as desorption solvent. Under the optimal conditions, linearity was observed over a range of 0.020-10.00 µg mL-1 with detection limits of 0.015 µg mL-1 and 0.010 µg mL-1 for hexanal and heptanal, respectively. The applicability of the HF-SPME MTMOS-MPTMOS for analysis of hexanal and heptanal in human urine sample was proven from the quantitative recoveries (&gt, 90) achieved. The HF-SPME MTMOS-MPTMOS offers an attractive alternative for rapid and convenient extraction tool and showed good potential for analysis of hexanal and heptanal from aqueous samples.

Sensitive determination of plasma protein binding of cationic drugs using mixed-mode solid-phase microextraction

Freely dissolved concentrations are considered to be the most relevant concentration in pharmacology and toxicology, as they represent the active concentration available for interaction with its surroundings. Here, a solid-phase microextraction (SPME) coating that combines octadecyl and propylsulfonic acid groups as strong cation exchange sites, known as C18/SCX or “mixed-mode” SPME, is used to measure freely dissolved concentrations of amitriptyline, amphetamine, diazepam and tramadol to different binding matrices, including bovine serum albumin (BSA), human serum albumin (HSA), human plasma and human whole blood. A potential confounding factor in binding studies is that proteins may sorb to the fiber coating leading to incorrect measurement of protein sorption or changes in uptake kinetics to the fiber coating. Sorption of bovine serum albumin (BSA) was observed and quantified using a Lowry assay. BSA binds to the C18/SCX fiber in small amounts, but large changes in uptake kinetics were not observed. All experiments were performed at equilibrium. In addition, however, the effect of depletion and non-equilibrium extraction on the estimation of protein binding affinities was also studied. Binding affinities to BSA and human serum albumin (HSA) were calculated as log KBSA or log KHSA. These values were very similar to reported literature values. Sampling at either equilibrium or non-equilibrium resulted in similar binding affinities. Furthermore, SPME fibers were used to measure freely dissolved concentrations in undiluted human plasma and whole blood. Analysis of SPME extracts could be performed using HPLC-UV or HPLC with fluorescence detection without prior clean-up of the samples. Measured bound fractions in plasma using this SPME approach were comparable to literature reference values. Bound fractions in whole blood were always higher than in plasma, due to red blood cell partitioning. This work shows the potential of SPME as sampling tool for freely dissolved concentrations, especially for highly protein-bound compounds. Conventional SPME coatings such as polyacrylate (PA) or polydimethylsiloxane (PDMS) might be lacking sensitivity when sampling the small neutral fraction of highly protein-bound positively charged compounds, but the C18/SCX fiber is able to sorb the charged species of organic cations, thereby improving sensitivity for these types of compounds.

Design and optimization of a total vaporization technique coupled to solid-phase microextraction.

Solid-phase microextraction (SPME) is a popular sampling technique in which chemical compounds are collected with a sorbent-coated fiber and then desorbed into an analytical instrument such as a liquid or gas chromatograph. Typically, this technique is used to sample the headspace above a solid or liquid sample (headspace SPME), or to directly sample a liquid (immersion SPME). However, this work demonstrates an alternative approach where the sample is totally vaporized (total vaporization SPME or TV-SPME) so that analytes partition directly between the vapor phase and the SPME fiber. The implementation of this technique is demonstrated with polydimethylsiloxane-divinylbenzene (PDMS-DVB) and polyacrylate (PA) coated SPME fibers for the collection of nicotine and its metabolite cotinine in chloroform extracts. The most important method parameters were optimized using a central composite design, and this resulted in an optimal extraction temperature (96 °C), extraction time (60 min), and sample volume (120 μL). In this application, large sample volumes up to 210 μL were analyzed using a volatile solvent such as chloroform at elevated temperatures. The sensitivity of TV-SPME is nearly twice that of liquid injection for cotinine and nearly 6 times higher for nicotine. In addition, increased sampling selectivity of TV-SPME permits detection of both nicotine and cotinine in hair as biomarkers of tobacco use where in the past the detection of cotinine has not been achieved by conventional SPME.

Solid-phase Microextraction (SPME) with Stable Isotope Calibration for Measuring Bioavailability of Hydrophobic Organic Contaminants

Solid-phase microextraction (SPME) is a biomimetic tool ideally suited for measuring bioavailability of hydrophobic organic compounds (HOCs) in sediment and soil matrices. However, conventional SPME sampling requires the attainment of equilibrium between the fiber and sample matrix, which may take weeks or months, greatly limiting its applicability. In this study, we explored the preloading of polydimethylsiloxane fiber with stable isotope labeled analogs (SI-SPME) to circumvent the need for long sampling time, and evaluated the performance of SI-SPME against the conventional equilibrium SPME (Eq-SPME) using a range of sediments and conditions. Desorption of stable isotope-labeled analogs and absorption of PCB-52, PCB-153, bifenthrin and cis-permethrin were isotropic, validating the assumption for SI-SPME. Highly reproducible preloading was achieved using acetone-water (1:4, v/v) as the carrier. Compared to Eq-SPME that required weeks or even months, the fiber concentrations (Cf) under equilibrium could be reliably estimated by SI-SPME in 1 day under agitated conditions or 20 days under static conditions in spiked sediments. The Cf values predicted by SI-SPME were statistically identical to those determined by Eq-SPME. The SI-SPME method was further applied successfully to field sediments contaminated with PCB 52, PCB 153, and bifenthrin. The increasing availability of stable isotope labeled standards and mass spectrometry nowadays makes SI-SPME highly feasible, allowing the use of SPME under nonequilibrium conditions with much shorter or flexible sampling time.

Assessing bioavailability of DDT and metabolites in marine sediments using solid‐phase microextraction with performance reference compounds

Solid-phase microextraction (SPME) has often been used to estimate the freely dissolved concentration (Cfree ) of organic contaminants in sediments. A significant limitation in the application of SPME for Cfree measurement is the requirement for attaining equilibrium partition, which is often difficult for strongly hydrophobic compounds such as DDT. A method was developed using SPME with stable isotope-labeled analogues as performance reference compounds (PRCs) to measure Cfree of DDT and metabolites (DDTs) in marine sediments. Six (13) C-labeled or deuterated PRCs were impregnated into polydimethylsiloxane (PDMS) fiber before use. Desorption of PRCs from PDMS fibers and absorption of DDTs from sediment were isotropic in a range of sediments evaluated ex situ under well-mixed conditions. When applied to a historically contaminated marine sediment from a Superfund site, the PRC-SPME method yielded Cfree values identical to those found by using a conventional equilibrium SPME approach (Eq-SPME), whereas the time for mixing was reduced from 9 d to only 9 h. The PRC-SPME method was further evaluated against bioaccumulation of DDTs by Neanthes arenaceodentata in the contaminated sediment with or without amendment of activated carbon or sand. Strong correlations were consistently found between the derived equilibrium concentrations on the fiber and lipid-normalized tissue residues for DDTs in the worms. Results from the present study clearly demonstrated the feasibility of coupling PRCs with SPME sampling to greatly shorten sampling time, thus affording much improved flexibility in the use of SPME for bioavailability evaluation.

Developments and Trends of Molecularly Imprinted Solid-Phase Microextraction

This review focuses on a solid-phase microextraction (SPME) method coupled with molecularly imprinted polymers (MIPs), namely molecularly imprinted solid-phase microextraction (MISPME). The first two sections discuss the summaries of conventional SPME and MIPs. The third section reviews the development of MISPME in past years, including the preparation of MISPME, and the applications to compounds in real samples.

Robust aptamer sol–gel solid phase microextraction of very polar adenosine from human plasma

Conventional solid phase microextraction (SPME) has a limited capacity to extract very polar analytes, such as adenosine. To solve this problem, aptamer conjugating sol–gel methodology was coupled with an SPME fiber. According to the authors’ knowledge, this is the first reported use of aptamer SPME. The fiber of aptamer sol–gel SPME with a mesoporous structure has high porosity, large surface area, and small water contact angle. Rather than employing direct entrapment, covalent immobilization was the dominant method of aptamer loading in sol–gel. Aptamer sol–gel fiber captured a specified analyte from among the analog molecules, thereby, exhibiting an excellent selective property. Compared with commercial SPME fibers, this aptamer fiber was suitable for extracting adenosine, presenting an extraction efficiency higher than 20-fold. The values of repeatability and reproducibility expressed by relative standard deviation were low (9.4%). Interestingly, the sol–gel network enhanced the resistance of aptamer SPME to both nuclease and nonspecific proteins. Furthermore, the aptamer sol–gel fiber was applied in human plasma with LOQ 1.5μg/L, which is an acceptable level. This fiber also demonstrates durability and regeneration over 20-cycles without significant loss of efficiency. Given the various targets (from metal ions to biomacromolecules and cells) of aptamers, this methodology will extend the multi-domain applications of SPME.

Dispersive liquid–liquid microextraction based on solidification of floating organic droplets followed by high performance liquid chromatography for the determination of duloxetine in human plasma

A novel dispersive liquid–liquid microextraction method based on solidification of floating organic droplets (DLLME-SFO) technique was developed for the determination of duloxetine in human plasma samples by high performance liquid chromatography with fluorescence detection (HPLC-FLD). During the extraction procedure, plasma protein was precipitated by using a mixture of zinc sulfate solution and acetonitrile. After the protein precipitation step, duloxetine in an alkaline sample solution was quickly extracted by DLLME-SFO with 50μL of 1-undecanol (extractant). Disperser was unnecessary because the small amount of remaining acetonitrile, which acts as a protein precipitating reagent, was also employed as a disperser; therefore, organic solvent consumption was reduced as much as possible. The emulsion was centrifuged and then fine droplets were floated to the top of the sample solution. The floated droplets were solidified in an ice bath and easily transferred. Various DLLME-SFO parameters such as extractant type, extractant amount, ionic strength, pH and extraction time were optimized. The chromatographic separation of duloxetine was carried out using ethanol as mobile phase. Validation of the method was performed with respect to linearity, intra- and inter-day accuracy and precision, limit of quantification (LOQ), and recovery. Calibration curves for duloxetine showed good linearity with correlation coefficients (r2) higher than 0.99. The method showed good precision and accuracy, with intra- and inter-assay coefficients of variation less than 15% (LOQ: less than 20%) at all concentrations. The recovery was carried out following the standard addition procedure with yields ranging from 59.6 to 65.5%. A newly developed environmentally friendly method was successfully applied to the pharmacokinetic study of duloxetine in human plasma and was shown to be an alternative green approach compared with the conventional solid-phase microextraction (SPME) and dispersive liquid–liquid microextraction (DLLME) techniques.