Methods for coating solid-phase microextraction fibers with carbon nanotubes

Solid-phase microextraction - a future technique in pharmacology and coating trends

Traditional sample preparation techniques based on liquid-liquid extraction (LLE) or solid-phase extraction (SPE) often suffer from a major error due to the matrix effects caused by significant co-extraction of matrix components. The implementation of a modern extraction technique such as solid-phase microextraction (SPME) was aimed at reducing analysis time and the use of organic solvents, as well as eliminating pre-analytical and analytical errors. Solid-phase microextraction (SPME) is an innovative technique for extracting low molecular weight compounds (less than 1500 Da) from highly complex matrices, including biological matrices. It has a wide range of applications in various types of analysis including pharmaceutical, clinical, metabolomics and proteomics. SPME has a number of advantages over other extraction techniques. Among the most important are low environmental impact, the ability to sample and preconcentrate analytes in one step, simple automation, and the ability to extract multiple analytes simultaneously. It is expected to become, in the future, another method for cell cycle research. Numerous available literature sources prove that solid-phase microextraction can be a future technique in many scientific fields, including pharmaceutical sciences. This paper provides a literature review of trends in SPME coatings and pharmacological applications.

Magnetic phytic acid-modified kapok fiber biochar as a novel sorbent for magnetic solid-phase extraction of antidepressants in biofluids

BACKGROUND

Therapeutic drug monitoring (TDM) of antidepressants is essential for monitoring patient medication to avoid drug toxicity, complications, or nonadherence. Chromatographic techniques with high sensitivity and reproducibility are the main detection method for antidepressants. Effective pretreatment of biological sample processes is necessary prior to instrumental analysis. Magnetic solid-phase extraction (MSPE) has received much attention for its advantages of simple operation, rapidity, cost-effectiveness and low organic solvent consumption. Therefore, the development of a suitable and green magnetic sorbent for the detection of antidepressants in plasma and urine is apparently necessary. (88) RESULTS: A magnetic phytic acid-modified kapok fiber biochar sorbent (Fe3O4/PAKFBC) was successfully synthesized by pyrolytic impregnation and physical milling methods. Fe3O4/PAKFBC exhibited a large specific surface area (214 m2 g-1) and a rich pore structure (5-10 nm). The extraction equilibrium, using 10 mg Fe3O4/PAKFBC, can be completed in about 1 min. The density functional theory (DFT) results showed that the adsorption mechanism of Fe3O4/PAKFBC on the six antidepressants mainly included electrostatic interactions, van der Waals interactions, π-π interactions and weak hydrogen bonding. Examination using the greenness assessment tools showed that the developed method exhibited excellent greenness. By combining with liquid chromatography-ultraviolet (LC-UV), a quantitative method with good linearity (R2 > 0.993) and relative recoveries (92.4-107.7%) and negligible matrix effect (-11.5-6.0%) was developed. The Fe3O4/PAKFBC successfully detected six antidepressants in plasma and urine samples, requiring no pH adjustment with buffer salts. (142) SIGNIFICANCE: The environmental sustainability of the proposed methods was affirmed by six greenness evaluation tools, all indicating exceptional eco-friendliness. The Fe3O4/PAKFBC demonstrated outstanding greenness in both its creation and analytical application, proving highly effective in real sample applications and showcasing potential for broader use. This study contributes to a deeper and broader understanding of the microscopic adsorption mechanism, which can help in the optimization and development of more green sorbents. (69).

Nanoporous carbon fiber derived from Cu-BDC metal organic framework @pencil graphite as a sorbent for solid phase microextraction of acetamiprid and imidacloprid

Solid-phase microextraction (SPME) is a sample pretreatment technique for enrichment of trace level of compounds from complex matrices. The fiber coating, as an extraction phase, is the significant part of SPME, which specifying the analytical performance of the developed SPME. In this study, a novel in situ fabricated Cu@porous carbon fiber that derived from copper benzene-1,4-dicarboxylate framework@pencil graphite (Cu-BDC MOF@PG) fiber was prepared as a SPME fiber. The Cu-BDC MOF was electrodeposited on the surface of pencil graphite. The Cu@porous carbon fiber with nanoporous structure was constructed by the direct carbonization of the electrosynthesized fiber. The Cu@porous carbon fiber showed high analytical performance for direct immersion SPME (DI-SPME) of acetamiprid and imidacloprid in fruit and vegetable samples. The SPME method was coupled by high-performance liquid chromatography-ultraviolet detection (SPME-HPLC-UV) for determination of the analytes. Under the optimized condition, good linear ranges (1-500 μg L-1 and 0.5-200 μg L-1) and acceptable limits of detection (LODs = 0.30 and 0.15 μg L-1), appropriate spiking recoveries in the range 87-109.0% were attained for acetamiprid and imidacloprid, respectively. Intra- and inter-day relative standard deviations were found within the ranges of 2.35-3.46% and 3.30-3.70%, respectively. These results signify promising potential of the in situ fabricated porous carbon fiber for SPME applications. Considering that most of the pencil graphite is made of carbon, after the carbonization of the Cu-BDC MOF@PG fiber, a unified porous carbon fiber is obtained. Compared to other reported procedures, in situ direct carbonization of Cu-BDC MOF@PG fiber was a one-step and straightforward method to fabricate carbon fiber.

Biochar nanosphere-functionalized carbon fibers for in-tube solid-phase microextraction of polycyclic aromatic hydrocarbons in environmental water followed by liquid chromatography and diode array detection

In order to improve the extraction ability of carbon fibers (CFs) for microextraction of polycyclic aromatic hydrocarbons (PAHs), biochar nanospheres derived from glucose were in-situ grown onto the surface of CFs via hydrothermal synthesis. The surface morphology and elemental composition of biochar nanospheres-CFs were investigated by scanning electron microscopy and X-ray photoelectron spectroscopy. Thereafter, the biochar nanosphere-CFs were pulled into the polyetheretherketone tube for solid-phase microextraction, and the tube was combined with high-performance liquid chromatography-diode array detector to online detect PAHs. With the help of π-stacking, hydrophobic, and hydrophilic effect of biochar nanospheres, the extraction efficiency of CFs was greatly enhanced (enrichment factor increased by 293% compared with  the original). The conditions affecting the analytical performance (sampling volume, sampling rate, methanol content, and desorption time) were investigated. Under the optimal conditions, an online analytical method for microextraction and determination of several PAHs was developed, and satisfactory results were achieved. The limits of detection were 0.003-0.010 ng mL-1 owing to high enrichment effect (2973-3600), linearity ranged from  0.010-15.0 ng mL-1, and relative standard deviations were 0.4%-1.6% (intra-day) and 2.4%-4.4% (inter-day), respectively. The method was applied to analyze environmental water samples (rain water, snow water, and river water), and spiked recoveries within 80.0%-119% were obtained.

Carbon nanotubes-assisted solid-phase microextraction for the extraction of gasoline in fire debris samples

Gasoline is one of the most encountered ignitable liquids (IL) in fire debris analysis. The extraction of gasoline from fire debris samples presents challenges due to the complicated nature of multicomponent mixtures. This research work proposed a novel carbon nanotube-assisted solid phase microextraction (CNT-SPME) fiber coupled with gas chromatography and mass spectrometry (GC/MS) to determine gasoline residues for fire debris analysis. The CNT-SPME fiber was prepared by a sequential coating of polydopamine, epoxy, and CNTs on a stainless-steel wire. The extraction capabilities of the CNT-SPME fiber for gasoline and its major aromatic groups (xylenes, alkylbenzenes, indanes, and naphthalenes) from neat and spiked samples were promising, with linear dynamic ranges of 0.4-12.5 and 3.1-12.5 µg 20-mL^-1 headspace vial, respectively. The average relative standard deviations and accuracies for all concentration ranges in this work were lower than 15%. The relative recovery of the CNT-SPME fiber for all aromatic groups ranged from 28 ± 3% to 59 ± 2%. Additionally, the CNT-SPME fiber showed a higher selectivity for the naphthalenes group in gasoline, as indicated by the experimental outcome using a pulsed thermal desorption process of the extracts. We envision the nanomaterial-based SPME offers promising opportunities for extracting and detecting other ILs to support fire investigation.

A Hybrid Stainless-Steel SPME Microneedle Electrode Sensor for Dual Electrochemical and GC-MS Analysis

A mechanically robust in-tube stainless steel microneedle solid phase microextraction (SPME) platform for dual electrochemical and chromatographic detection has been demonstrated. The SPME microneedle was fabricated by layer-by-layer (LbL) in-tube coating, consisting of carbon nanotube (CNT)/cellulose nanocrystal (CNC) film layered with an electrically conductive polyaniline (PANI) hydrogel layer (PANI@CNT/CNC SPME microneedle (MN)). The PANI@CNT/CNC SPME MN showed effective analysis of caffeine by GC-MS with an LOD of 26 mg/L and excellent precision across the dynamic range. Additionally, the PANI@CNT/CNC SPME MN demonstrated a 67% increase in sensitivity compared to a commercial SPME fiber, while being highly robust for repeated use without loss in performance. For electrochemical detection, the PANI@CNT/CNC SPME MN showed excellent performance for the detection of 3-caffeoylquinic acid (3-CQA). The dynamic range and limits of detection (LOD) for 3-CQA analysis were 75-448 mg/L and 11 mg/L, respectively. The PANI@CNT/CNC SPME MN was demonstrated to accurately determine the caffeine content and 3-CQA in tea samples and dark roast coffee, respectively. The PANI@CNT/CNC SPME MN was used for semiquantitative antioxidant determination and composition analysis in kiwi fruit using electrochemistry and SPME-coupled GC-MS, respectively.

Recent applications of organic molecule-based framework porous materials in solid-phase microextraction for pharmaceutical analysis

Sample preparation is an indispensable part of detection of complex samples in pharmaceutical analysis. Solid-phase microextraction (SPME) has obtained a lot of attention due to its advantages of time saving, less solvent and easily automation. A variety of functional materials are used as sorbents in SPME to carry out selective and high extraction. This review centers around the recent applications of organic molecule-based framework porous materials, such as metal organic frameworks (MOFs) and covalent organic frameworks (COFs), as SPME coating materials mainly focus on pharmaceutical analysis in food, environment, and biological samples. Four representative extraction devices are introduced, including on-fiber SPME, in-tube SPME, thin film SPME, stir bar SPME. The application prospect of other organic porous materials as sorbents for pharmaceutical analysis are also discussed, such as hyper crosslinked polymers (HCPs) and conjugated microporous polymers (CMPs). The progresses and discusses are provided to offer references for further research focusing on application and development of organic molecule-based framework porous materials in the field of SPME.

GNP/Al-MOF nanocomposite as an efficient fiber coating of headspace solid-phase micro-extraction for the determination of organophosphorus pesticides in food samples

The synthesis and utilization of a high porous nanocomposite comprising MIL-53(Al) metal-organic framework (Al-MOF) and graphene nanopowder (GNP) is reported as a fiber coating for headspace solid-phase micro-extraction (HS-SPME) of selected organophosphorus pesticides (OPPs) from apple, potato, grape juice, tomato, and river water. The adsorbed OPPs on the coated fiber were subsequently determined using GC-MS. Several parameters affecting the efficiency of extraction including time and temperature of extraction, desorption condition of extracted analytes, pH and agitation of sample solution, and salt concentration were investigated. The optimum extraction condition was achieved at 70 °C with an extraction time of 40 min, pH = 4-8, and NaCl concentration of 6.0% (w/v). The best condition of desorption were observed at 280 °C for 2.0 min under a flow of helium gas in the GC inlet. Under optimal conditions, the detection limits ranged from 0.2 to 1.5 ng g^-1 and the linear ranges between 0.8 and 600 ng g^-1. The proposed method showed very good repeatability with RSD values ranging from 4.5 to 7.3% (n = 5). The relative recoveries were between 88% and 109% at the spiked level of 25.0 ng g^-1 for the tomato sample. The fabricated fiber exhibited good enrichment factor (62-195) at optimum condition of HS-SPME. The applied HS-SPME technique is facile, fast, and inexpensive. The thermally stable GNP/Al-MOF exhibited a high sensitivity toward OPPs. So, this nanocomposite can be considered as a sorbent for the micro-extraction of other pesticides in food.

Evaluation of New, Sputtered Carbon SPME Fibers with a Multi-Functional Group Test Mixture

We report the first fabrication of sputtered carbon, solid-phase microextraction (SPME) fibers. These fibers have competitive extraction capabilities compared with the commercial carbon wide range (CWR) SPME fiber. This report also includes a demonstration of a newly developed SPME test mix that includes 15 different compounds with a wide range of functional groups and chemical properties. The fiber fabrication process involves sputtering carbon onto fused silica fibers, and the effects of throw distance on the morphology of the carbon coatings were studied. Four different carbon coating thicknesses were evaluated, with PDMS added as a stationary phase. These fibers were characterized with multiple analytical techniques, including scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), water contact angle (WCA) goniometry, as well as headspace (HS) and direct immersion (DI)–SPME–GC–MS. The best (11.5 µm) sputtered carbon SPME fibers, with and without PDMS, were evaluated using the new evaluation mix and compared with the commercial CWR fiber and a previously sputtered/developed silicon fiber. The new probe mix helped elucidate differences among the fibers, which would have been missed by current commercial test mixes. The sputtered carbon SPME fibers showed similar functional group selectivity as commercial CWR fibers. However, the sputtered carbon fibers showed higher responses per volume compared with the commercial CWR fiber, indicating the porous morphology of the sputtered carbon has the ability to overcome large phase thickness/volume discrepancies and increase the relative recovery for various compounds.

On the use of metal-organic frameworks for the extraction of organic compounds from environmental samples

The determination of trace metals and organic contaminants in environmental samples, such as water, air, soil, and sediment, is until today a challenging process for the analytical chemistry. Metal-organic frameworks (MOFs) are novel porous nanomaterials that are composed of metal ions and an organic connector. These materials are gaining more and more attention due to their superior characteristics, such as high surface area, tunable pore size, mechanical and thermal stability, luminosity, and charge transfer ability between metals and ligands. Among the various applications of MOFs are gas storage, separation, catalysis, and drug delivery. Recently, MOFs have been successfully introduced in the field of sample preparation for analytical chemistry and they have been used for sample pretreatment of various matrices. This review focuses on the applications of MOFs as novel adsorbents for the extraction of organic compounds from environmental samples.

A simple and efficient Solid-Phase Microextraction - Gas Chromatography - Mass Spectrometry method for the determination of fragrance materials at ultra-trace levels in water samples using multi-walled carbon nanotubes as innovative coating

The occurrence of emerging contaminants is becoming of increasing importance to assess the impact of anthropogenic activities onto the environment. The present study reports for the first time the development and validation of an efficient method for the simultaneous determination of fragrance materials in water samples based on the use of a novel multiwalled carbon nanotubes (MWCNTs)-based solid-phase microextraction coating. Helical MWCNTs were selected as adsorbent material due to their outstanding extraction performance. The multicriteria method of desirability functions allowed the optimization of the experimental conditions in terms of extraction time and extraction temperature. Validation proved the reliability of the method for the determination of the analytes at ultra-trace levels, obtaining detection limits in the 0.2-13 ng/L range, good precision, with relative standard deviations lower than 20% and recovery rates in the 80 ± 12%-111 ± 11%. Superior enrichment factors compared to commercial fibers were also calculated. Finally, applicability to real sample analysis was demonstrated.

Carbon aerogel-based solid-phase microextraction coating for the analysis of organophosphorus pesticides

The current study is focused on the in situ synthesis of a carbon aerogel (CA)-based solid-phase microextraction (SPME) fiber coating on stainless steel wire and evaluation of the suitability of CAs as SPME coating materials for the analysis of selected organophosphorus pesticides (OPPs) contained in environmental samples. A CA-based coating was obtained by pyrolyzing organic aerogels, which were prepared by the sol-gel polymerization of formaldehyde and 5-methylresorcinol, an oil shale processing by-product. The results demonstrated, for the first time, the in situ synthesis of a CA-based SPME fiber coating on stainless steel wire and its suitability for the extraction and preconcentration of six OPPs. Main parameters affecting the extraction efficiency were investigated and optimized. The direct immersion (DI)-SPME procedure combined with gas chromatography-mass spectrometry (GC-MS) for the simultaneous analysis of selected OPPs was successfully applied to the efficient and sensitive determination of analytes of interest in environmental matrices of honey and natural water samples. The developed CA-coated SPME fiber showed good linearity (R² = 0.981-0.994), low detection limits (0.11-0.83 μg L^-1) and satisfactory single fiber and fiber-to-fiber reproducibilities (8.8-12.3%, n = 5 and 11.4-17.2%, n = 3). The performance of the CA-coating was compared with that of commercially available SPME fiber coatings.

Helical multi-walled carbon nanotube-coated fibers for solid-phase microextraction determination of polycyclic aromatic hydrocarbons at ultra-trace levels in ice and snow samples

Polycyclic Aromatic Hydrocarbons (PAHs) detected in polar environment are recognized tracers of anthropogenic pollution. High sensitivity and selectivity are required for their analysis in ice and snow samples due to the presence at ultra-trace levels. In this study a solid-phase microextraction (SPME) gas chromatography-mass spectrometry (GC-MS) method for simultaneous determination of the 16 US-EPA priority pollutant PAHs in polar snow and ice samples was developed and validated. Helical multiwalled carbon nanotubes (HMWCNTs) were proposed for the first time as novel SPME coating. For optimization purposes a Central Composite Design and the multicriteria method of the desirability functions were applied to investigate the influence of extraction parameters, i.e. time and temperature as main factors. The optimal values were 68 °C for the extraction temperature and 60 min for the extraction time. The developed SPME-GC-MS method exhibited detection limits of 16 PAHs in the 0.1-1.2 ng/L range, a repeatability and an intermediate precision within 15% and 22% relative standard deviation, respectively, and good recovery rates in the 93.7 (± 0.1)-119.7 (± 0.2)% range for real spiked water sample, showing better analytical performance compared to commercial PDMS fibers. Enrichment factors in the 2670 (± 290)-142120 (± 580) range were calculated and a long fiber shelf-life with the possibility to reuse the fiber more than 200 times was achieved. Finally, the proposed method was successfully applied to the determination of PAHs in surface snow samples collected in April 2019 at Ny-Ålesund, Svalbard. Its application to the detection of PAHs in samples collected during monitoring campaigns in the polar regions is expected in the near future.

The effect of different binders on the comprehensive performance of solid phase microextraction fiber

Binders are significant components for the preparation of solid-phase microextraction (SPME) fibers. However, little attention has been paid to the effect of different binders. Considering their diverse properties, in this work, we select three kinds of commonly used binders including polydimethylsiloxane (PDMS), polyacrylonitrile (PAN) and Nafion, as well as introduce a new binder of poly (vinylidene fluoride) (PVDF) to synthetically study the influence of binders. By using the commercial active carbons (ACs) with different binders, four SPME fibers with uniform morphologies and comparative thicknesses (i.e., ACs-PDMS-coated, ACs-PAN-coated, ACs-Nafion-coated and ACs-PVDF-coated fibers) have been prepared successfully. The effect of binders on the pore structure of ACs is firstly investigated. It is found that PDMS and PAN would cause pore blocking, and the specific surface area of ACs coatings decreases from 1362 m² g^-1 to 280 and 196 m² g^-1, respectively. While the specific surface area of ACs-PVDF composite remains 940 m² g^-1. Based on SPME, the influences of acid/alkali, high temperature and matrix towards different fibers are further systematically surveyed. Finally, the enrichment performance of prepared fibers towards various organic pollutants is preliminarily discussed. The comparison results show that PVDF demonstrates outstanding stability in all aspects. Therefore, PVDF might be an excellent candidate for the preparation of SPME fiber. Moreover, all obtained results are expected to provide the reference value for the further development of novel SPME fibers.

Electrochemically Fabricated Solid Phase Microextraction Fibers and Their Applications in Food, Environmental and Clinical Analysis

Background:

Designing an analytical methodology for complicated matrices, such as biological and environmental samples, is difficult since the sample preparation procedure is the most demanding step affecting the whole analytical process. Nowadays, this step has become more challenging by the legislations and environmental concerns since it is a prerequisite to eliminate or minimize the use of hazardous substances in traditional procedures by replacing with green techniques suitable for the sample matrix.

Methods:

In addition to the matrix, the nature of the analyte also influence the ease of creating green analytical techniques. Recent developments in the chemical analysis provide us new methodologies introducing microextraction techniques and among them, solid phase microextraction (SPME) has emerged as a simple, fast, low cost, reliable and portable sample preparation technique that minimizes solvent consumption.

Results:

The use of home-made fibers is popular in the last two decades since the selectivity can be tuned by changing the surface characteristics through chemical and electrochemical modifications. Latter technique is preferred since the electroactive polymers can be coated onto the fiber under controlled electrochemical conditions and the film thicknesses can be adjusted by simply changing the deposition parameters. Thermal resistance and mechanical strength can be readily increased by incorporating different dopant ions into the polymeric structure and selectivity can be tuned by inserting functional groups and nanostructures. A vast number of analytes with wide range of polarities extracted by this means can be determined with a suitable chromatographic detector coupled to the system. Therefore, the main task is to improve the physicochemical properties of the fiber along with the extraction efficiency and selectivity towards the various analytes by adjusting the electrochemical preparation conditions.

Conclusion:

This review covers the fine tuning conditions practiced in electrochemical preparation of SPME fibers and in-tube systems and their applications in environmental, food and clinical analysis.

Meso-/microporous carbon as an adsorbent for enhanced performance in solid-phase microextraction of chlorobenzenes

There is urgent demand for the design of advanced coating materials for solid-phase microextraction (SPME) for water quality monitoring and assessment because of the global occurrence of chlorobenzenes (CBs). In this study, we proposed a dual-order activation method in which potassium hydroxide is used to modify pre-activated calcium citrate to synthesize a highly developed meso-/microporous carbon (MMC). The as-obtained MMC presented well-developed porosity with a super-high specific surface area (2638.09 m² g^-1), abundant meso-/micropores (0.5-10 nm), high hydrophobicity, excellent thermal stability (>720 °C), and a partly graphitized structure. As a coating material for headspace-SPME, the MMC-coated fiber exhibited outstanding extraction capability for CBs (up to 48.5 times higher than that of commercial fibers), which may be attributed to multiple interactions between the MMC and the pollutants, including size selectivity, micropore filling, π-π stacking and hydrophobicity. Finally, a satisfactory method using an MMC-coated fiber coupled with gas chromatography and electron capture detection was developed with good linearity (1-1000 ng L^-1, R² > 0.9982), high enrichment efficiencies (enrichment factors, 861-7819), low limits of detection (0.003-0.072 ng L^-1), excellent repeatability (0.7-5.3%) and reproducibility (1.7-5.1%), and outstanding recoveries (90.18-103.02%) when applied to determine trace CBs in real water samples. These results suggest that MMC is a promising coating material for the SPME of CBs.

Application of powdered activated carbon coating to fabrics in a hybrid filter to enhance mercury removal

Elemental mercury (Hg⁰) is predominant constituent of flue gas emitted from coal-fired power plants. Adsorption has been considered the best available technology for removal of Hg⁰ from flue gas. However, adsorbent injection increases the amount of ash generated. In the present study, powdered activated carbon (PAC) was coated on polytetrafluoroethylene/glass fiber filters to increase Hg⁰ removal while concurrently reducing the amount of ash generated. The optimal PAC coating rate was determined in laboratory experiments to ensure better Hg⁰ removal with low pressure drop. When PAC of particle size less than 45 μm was used, and the areal density was 50 g/m², the pressure drop remained under 30 Pa while the Hg⁰ removal efficiency increased to 15.8% from 4.3%. The Hg⁰ removal efficiency also increased with decrease in filtration velocity. The optimal PAC coating rate was applied on a hybrid filter (HF), which was combined with a bag filter and an electrostatic precipitator in a single chamber. Originally designed to remove fine particulates matter, it was retrofitted to the flue gas control device for simultaneous Hg⁰ removal. By employing the PAC coating, the Hg removal efficiency of the HF increased to 79.79% from 66.35%. Also, a temporary reduction in Hg removal was seen but this was resolved following a cleaning cycle in which the dust layer was removed.

Trace analysis by ion mobility spectrometry: From conventional to smart sample preconcentration methods. A review

Ion mobility spectrometry (IMS) is a rapid and high sensitive technique widely used in security and forensic areas. However, a lack of selectivity is usually observed in the analysis of complex samples due to the scarce resolution of the technique. The literature concerning the use of conventional and novel smart materials in the pretreatment and preconcentration of samples previous to IMS determinations has been critically reviewed. The most relevant strategies to enhance selectivity and sensitivity of IMS determinations have been widely discussed, based in the use of smart materials, as immunosorbents, aptamers, molecularly imprinted polymers (MIPs), ionic liquids (ILs) and nanomaterial. The observed trend is focused on the development of IMS analytical methods in combination of selective sample treatments in order to achieve quick, reliable, sensitive, and selective methods for the analysis of complex samples such as biological fluids, food, or environmental samples.

A chromium(III) oxide-coated steel wire prepared by arc ion plating for use in solid-phase microextraction of aromatic hydrocarbons

The authors introduce an arc ion plating method for the deposition of chromium oxide (Cr₂O₃) on a steel wire substrate, and its use as a coating for solid phase microextraction. The coating has a micro- and nano-scaled structure after annealing at 700 °C. It is found that Cr₂O₃ exhibits a good extraction capability for the aromatic hydrocarbons naphthalene, anthracene, fluorene, fluoranthene, and biphenyl. Following desorption by high temperature at 300 °C, the analytes were quantified by gas chromatography (GC). The limits of detection are in the range between 20 and 200 ng·L^-1, and calibration plots are linear within a wide range (0.2 to 400 μg·L^-1). The coating has excellent mechanical properties, with a hardness is as high as 31.7 GPa, and the adhesion strength between coating and substrate reaches 20.1 N (corresponding to the critical Hertzian contact stress of 10 GPa). This, along with the chemical and thermal stability of the Cr₂O₃ coating, endows the wire with a long operational life. It was used for at least 100 times without any obvious decline of extraction capability. Graphical abstract An arc ion plating method was introduced for the deposition of chromium oxide (Cr₂O₃) on a steel wire substrate, and its use as a coating for solid phase microextraction with high mechanical strength, stability, and long operational lifetime.

Review of geometries and coating materials in solid phase microextraction: Opportunities, limitations, and future perspectives

The development of new support and geometries of solid phase microextraction (SPME), including metal fiber assemblies, coated-tip, and thin film microextraction (TFME) (i.e. self-supported, fabric and blade supported), as well as their effects on diffusion and extraction rate of analytes were discussed in the current review. Application of main techniques widely used for preparation of a variety of coating materials of SPME, including sol-gel technique, electrochemical and electrospinning methods as well as the available commercial coatings, were presented. Advantages and limitations of each technique from several aspects, such as range of application, biocompatibility, availability in different geometrical configurations, method of preparation, incorporation of various materials to tune the coating properties, and thermal and physical stability, were also investigated. Future perspectives of each technique to improve the efficiency and stability of the coatings were also summarized. Some interesting materials including ionic liquids (ILs), metal organic frameworks (MOFs) and particle loaded coatings were briefly presented.

Nanostructured metal–organic frameworks, TMU-4, TMU-5, and TMU-6, as novel adsorbents for solid phase microextraction of polycyclic aromatic hydrocarbons

Zn(ii) based metal–organic frameworks were coated onto stainless steel wire and applied to the headspace solid phase microextraction of PAHs.