Gas-cycle-assisted headspace solid-phase microextraction coupled with gas chromatography for rapid analysis of organic pollutants

In situ fabrication of covalent organic frameworks on solid-phase microextraction probes coupled with electrospray ionization mass spectrometry for enrichment and determination of androgens in biosamples

Solid-phase microextraction (SPME) coupled with electrospray ionization mass spectrometry (ESI-MS) was developed for rapid and sensitive determination of endogenous androgens. The SPME probe is coated with covalent organic frameworks (COFs) synthesized by reacting 1,3,5-tri(4-aminophenyl)benzene (TPB) with 2,5-dioctyloxybenzaldehyde (C8PDA). This COFs-SPME probe offers several advantages, including enhanced extraction efficiency and stability. The analytical method exhibited wide linearity (0.1-100.0 µg L-1), low limits of detection (0.03-0.07 µg L-1), high enrichment factors (37-154), and satisfactory relative standard deviations (RSDs) for both within one probe (4.0-14.8%) and between different probes (3.4-12.7%). These remarkable performance characteristics highlight the reliability and precision of the COFs-SPME-ESI-MS method. The developed method was successfully applied to detect five kinds of endogenous androgens in female serum samples, indicating that the developed analytical method has great potential for application in preliminary clinical diagnosis.

Three-dimensional rose-like zinc oxide fiber coating for simultaneous extraction of polychlorinated biphenyls and polycyclic aromatic hydrocarbons by headspace solid phase microextraction

The three-dimensional (3D) rose-like zinc oxide (ZnO) material was prepared by a simple one-step CTAB-assisted hydrothermal strategy and used as a headspace solid-phase microextraction (HS-SPME) coating. Polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) were analyzed by gas chromatography with flame ionization detector (GC-FID), and conclusively applied to ultrasensitive detection in lake and river water. Compared with one-dimensional (1D) pencil-like ZnO, the layer-by-layer petal-like structure could fully expose mass adsorption sites on the surface, which could significantly improve the adsorption. The enrichment factors with 7535-8595 for PCBs and 3855-7320 for PAHs were achieved. The established method provided a satisfactory linear range (0.005-30 ng·mL-1), coefficient (R2 > 0.9978), ultra-low limit detection (1-3 pg·mL-1), and long service life (≥ 150 times). The recoveries of 83.42-120.86 % were obtained in the real detection application of lake and river water. This work demonstrated that 3D rose-like ZnO with low cost, simple synthesis, fast extraction ability and high enrichment performance was an ideal coating material, which was hoped to enrich other compounds with similar structures with PCBs and PAHs.

Surfactant-enhanced air-agitation liquid-liquid microextraction of polycyclic aromatic hydrocarbons from edible oil using magnetic deep eutectic solvent prior to HPLC determination

Herein, an air-agitation liquid-liquid microextraction procedure was developed for the extraction of several polycyclic aromatic hydrocarbons from edible oil samples. In this study, the extraction procedure was achieved using a new magnetic deep eutectic solvent as the extraction solvent, in which there was no need for centrifugation. To enhance the rate of extraction of the analytes from the samples, the method was promoted by the use of surfactant addition. The extracted analytes were determined by high-performance liquid chromatography with a diode array detector. The influence of various parameters on the extraction efficiency was studied by response surface methodology using a central composite design. Under optimal conditions, linear calibration curves for the target analytes were achieved in the range of 0.43-250 ng g-1. The limits of detection and quantification were in the ranges of 0.04-0.13 and 0.13-0.43 ng g-1, respectively. The repeatability of the method in terms of intra- and inter-day precision was ≤4.7% and ≤6.7%, respectively. The extraction recovery of the method ranged from 75 to 88%. The obtained results show that the proposed method is efficient for the analysis of the target analytes in various oil samples without obvious matrix effects. Pyrene was found in olive oil at a concentration of 42 ng g-1.

A simple and portable vacuum assisted headspace solid phase microextraction device coupled to gas chromatography based on covalent organic framework/metal organic framework hybrid for simultaneous analysis of volatile and semi-volatile compounds in soil

Various microextraction methods have demonstrated a positive effect when assisted by vacuum. However, working with such systems is often laborious, they often require expensive and non-portable vacuum pumps, and may even suck off some sample vapor or solid particles during the evacuation process. To address these issues, a simple, and affordable vacuum-assisted headspace solid-phase microextraction (HS-SPME) device was developed in this study. The device, named In Syringe Vacuum-assisted HS-SPME (ISV-HS-SPME), utilizes an adjustable 40 mL glass syringe as a vacuum provider and sampling vessel. A new fiber coating, made from a hybrid of covalent triazine-based frameworks and metal-organic frameworks (COF/MOF), was prepared and characterized by Fourier transform infrared spectrometry, field emission scanning electron microscopy, energy dispersive X-ray, X-ray diffraction, thermogravimetric analysis, and Brunauer-Emmett-Teller techniques for use in the ISV-HS-SPME. By optimizing parameters such as extraction temperature, extraction time, desorption temperature, desorption time, and, humidity using a simplex method, the ISV system was found to increase the extraction efficiency of polycyclic aromatic hydrocarbons (PAHs) and benzene, toluene, ethylbenzene, and xylenes (BTEX) in solid samples by up to 175%. The determinations were followed by GC-FID measurements. Compared to three commercially available fibers, the ISV-HS-SPME device with the COF/MOF (2DTP/MIL-101-Cr) fiber exhibited significantly higher peak areas for PAHs and BTEX. The linear dynamic ranges for BTEX and PAHs were 7.1-9000 ng g-1 and 0.23-9000 ng g-1, respectively, with limits of detection ranging from 2.1-5 ng g-1 for BTEX and 0.07-1.6 ng g-1 for PAHs. The relative standard deviation of the method was 2.6-7.8% for BTEX and 1.6-6.7% for PAHs. The ISV-HS-SPME was successfully used to simultaneously determine PAHs and BTEX in polluted soil samples with recoveries ranging from 80.4 to 108%.

A rapid and green GC-MS method for the sampling of volatile organic compounds in spices and flowers by concurrent headspace single-drop microextraction and solid-phase microextraction

The equilibrium rather than the exhaustive nature of headspace single-drop microextraction (HS-SDME) and headspace solid-phase microextraction (HS-SPME) allowed the concurrent sampling of volatile organic compounds (VOCs) on the same sample in the same vial in a dual extraction configuration. This has avoided the necessity of conducting a separate set of experiments and was found to produce results in the time duration of a single sample preparation experiment. The results obtained by HS-SDME were validated against those found by the standard method of HS-SPME. Rectilinear calibration was made for certain VOCs tested as analytes over the range of 0.01-8 μg g^-1, and the average values of R², LOD and LOQ were found to be, respectively, 0.9992, 1.9 ng g^-1 and 5.7 ng g^-1 in HS-SDME, and 0.9991, 3.1 ng g^-1 and 9.1 ng g^-1 in HS-SPME. The spiked recoveries and RSD were, respectively, 100.5% and 3.3% in HS-SDME and 98.1% and 3.6% in HS-SPME. HS-SDME is convenient to perform and produce results in a much cheaper way than HS-SPME and free from the inconveniences of memory effects. With GC-MS, this method has also been implemented as a rapid, reliable and green procedure (by GAPI and AGREE tools) for the sampling of VOCs in real samples of spices, flowers, and a beetle nut chewing sample illicitly containing tobacco.

Dynamic headspace solid-phase extraction at room temperature: a theoretical model, method, and application for propofol analysis

Herein, a simple dynamic headspace solid-phase extraction (DHS-SPE) process at room temperature was used for a material that is sensitive to increase in the temperature. A proposed method was implemented to rapidly extract propofol (PF) from a complex matrix before fluorescence spectroscopy analysis, within a short sampling time without involving a hot plate or stirrer. A mini diaphragm pump was used to circulate the headspace gas. As the headspace gas flows over the sample solution surface, bubbles form and release analytes from the liquid into the headspace. During the extraction process, the headspace gas passes through the coated metal foam as a sorbent that is placed in a homemade glass vessel and analytes are trapped from the gas phase. A theoretical model of DHS-SPE based on the consecutive first-order process is proposed in this study. A mathematical solution for the dynamic process of mass transfer was obtained by correlating the variation in analyte concentration in the headspace and adsorber with the pump speed and amount of analyte extracted to the solid phase. Using electrochemically Nafion-doped polypyrrole (PPy-Naf) film on nickel foam as the solid-phase coupled to fluorescence detection, a linear dynamic range over the concentration range of 100-500 nM with a detection limit of 15 nM was obtained. This method was applied successfully for PF determination in human serum sample matrices without the interference of co-administered drugs, such as cisatracurium, which have significant emission spectrum overlap. The developed method can lead to a new idea for sample pretreatment, which is compatible with many analytical techniques and has been successfully combined with fluorescence spectroscopy in this work. This format of sampling simplifies the transfer of analytes from complex matrices to the headspace for the extraction and preconcentration process, eliminating the heating step and the need for expensive equipment.

In Situ Rapid Electrochemical Fabrication of Porphyrin-Based Covalent Organic Frameworks: Novel Fibers for Electro-Enhanced Solid-Phase Microextraction

Electro-enhanced solid-phase microextraction (EE-SPME) is a bright separation and enrichment technique that integrates solid-phase microextraction with the electric field. It retains the excellent extraction performance of SPME technology while having the advantages of efficient driving of electric field and special interaction between the electric field and electrons in the molecules of material structure. Replacing conventional SPME fibers with highly efficient and highly conductive original EE-SPME fibers is critical for the practical applications of these technologies. Here, a novel fiber preparation strategy was proposed to obtain a highly conductive porphyrin-based covalent organic framework (POR-COF) by one-step electropolymerization. Benefiting from the excellent semiconducting properties of porphyrin groups, the POR-COF can be spontaneously polymerized on the fiber surface under an appropriate voltage within a few hours. Its performance was evaluated by the EE-SPME of phthalate esters (PAEs) from food and environmental samples, followed by gas chromatography-tandem triple quadrupole mass spectrometry (GC-MS/MS) technology. The results showed that the POR-COF fiber has been successfully used for the detection of trace PAEs in beverages, industrial wastewater, lake water, and oyster samples with high adsorption selectivity and satisfactory sensitivity. The remarkable extraction properties are mainly attributed to the synergistic effect from material characteristics and electrical parameters' control in the extraction process. The presented strategy for the controlled design and synthesis of highly conductive porphyrin-based covalent organic framework fibers offers prospects in developing EE-SPME technologies.

Poly(divinylbenzene) as a fiber coating for headspace solid-phase microextraction of polycyclic aromatic hydrocarbons from river water

Porous polydivinylbenzene microspheres with high specific surface area were prepared by distillation-precipitation polymerization, and were used as the coating material in headspace solid phase microextraction for extracting polycyclic aromatic hydrocarbons. Compared with the other reported sorbents, PDVB exhibits lower cost and higher extraction efficiency, and the enrichment factors can reach 5963-16 720.

Porous Hexagonal Boron Nitride as Solid-Phase Microextraction Coating Material for Extraction and Preconcentration of Polycyclic Aromatic Hydrocarbons from Soil Sample

Sample pretreatment plays important role in the analysis and detection of trace pollutants in complex matrices, such as environmental and biological samples. The adsorption materials of sample pretreatment receive considerable attention, which has a significant effect on the sensitivity and selectivity of the analytical method. In this work, the porous hexagonal boron nitride (h-BN) was utilized as a coating material of solid-phase microextraction (SPME) to extract and preconcentrate polycyclic aromatic hydrocarbons (PAHs) prior to separation and detection with GC-FID. Attributed to the multiple interactions including hydrophobicity, hydrogen bonding and strong π–π interaction, the h-BN coating showed excellent extraction performance for PAHs. Under the optimal conditions, the method showed the linear relationship in the range of 0.1–50 ng mL⁻¹ for acenaphthene, 0.05–50 ng mL⁻¹ for pyrene, and 0.02–50 ng mL⁻¹ for fluorene, phenanthrene and anthracene with a correlation coefficient (R²) not lower than 0.9910. The enrichment factors were achieved between 1526 and 4398 for PAHs with h-BN as SPME fiber coating. The detection limits were obtained in the range of 0.004–0.033 ng mL⁻¹, which corresponds to 0.08–0.66 ng g⁻¹ for soil. The method was successfully applied to analysis of real soil samples. The recoveries were determined between 78.0 and 120.0% for two soil samples. The results showed that h-BN material provided a promising alternative in sample pretreatment and analysis.

Electrocatalytic reduction of 4-nitrophenol over Ni-MOF/NF: understanding the self-enrichment effect of H-bonds

The chemical adsorption and active sites play a key role in electrocatalysis, so Ni-MOF/nickel foam was fabricated for efficiently reducing 4-nitrophenol (4-NP) without any sacrificial agents. The coordinated water molecules induced the formation of hydrogen bonds (H-bonds) with the nitro group, contributing to the self-enrichment of 4-NP. The reaction rate reached 0.351 μmol min^-1 mg^-1. Therefore, this work provides a new insight into the H-bond effect in the field of electrocatalysis.