Hollow Fiber Liquid-phase Microextraction Research Articles

Recent advances in green solvents-based liquid-phase microextraction techniques for chromatographic analysis of active components in traditional Chinese medicine.

Traditional Chinese medicine (TCM) is a treasure of China and a crucial part of traditional medicine in the world, particularly in many oriental countries. TCM is the core and basis of traditional medicine in clinical practice for numerous diseases, and performs important function in nutraceuticals and dietary supplements. However, it is extremely difficult to extract each active ingredient from TCM to elucidate the mechanism of TCM clinical efficacy due to numerous compounds in TCM, especially trace compounds. Consequently, liquid-phase microextraction (LPME) techniques, one of the main extraction methods of active ingredients in TCM, have attracted a considerable attention from researchers. In recent years, many novel green solvents based-LPME methods have been reported, such as single-drop microextraction (SDME), hollow-fiber liquid-phase microextraction (HF-LPME), dispersive liquid-liquid microextraction (DLLME), and electro-membrane extraction (EME). Therefore, in this review, we present an up-to-date and comprehensive summary of various LPME techniques, novel green solvents, and their applications in the analysis of active ingredients within the complex TCM samples. We provide a detailed overview of the fundamental principles, modes, and the critical process parameters of the LPME techniques. In addition, we compare different types of green solvents (i.e., deep eutectic solvents, ionic liquids, magnetic ionic liquids, supramolecular solvents, switchable solvents, among others), and the advantages and disadvantages of these solvents are critically evaluated, highlighting their suitability for various applications. Finally, we elucidate the merits and demerits of different LPME methods, discuss their practical applications, and explore their future research directions. This review aims to provide a valuable resource for researchers and practitioners in the field of TCM, promoting research development and application of the advanced and environmentally friendly sample pretreatment techniques.

Ionic liquids-based adsorbents for extraction and separation: A review emphasizing recent advances in sample preparation

Ionic liquids (ILs) exhibit remarkable physical and chemical properties, encompassing negligible vapor pressure, non-flammability, high thermal stability and mechanical robustness. Moreover, ILs can be readily tailored for specific functions by altering the combination of cations and anions. These unique attributes have led to the widespread adoption of ILs as highly efficient adsorbents in sample preparation. To meet the requirements of various applications, ILs are often immobilized or functionalized. This review summarizes the primary types of currently available ILs-based adsorbents, including poly(ionic liquids), ILs-modified silica-based adsorbents, ILs-modified carbon-based adsorbents, ILs@metal–organic frameworks composite adsorbents, and ILs@covalent organic frameworks composite adsorbents. Additionally, the applications of ILs-based adsorbents in sample preparation techniques such as dispersive liquid–liquid microextraction, single-drop microextraction, hollow fiber liquid-phase microextraction, solid-phase extraction, magnetic solid-phase extraction, and solid-phase microextraction are introduced. Furthermore, the review provides insights into the challenges and prospects for the future development of ILs-based adsorbents.

Natural deep eutectic solvents and natural solid biosorbents in microextraction techniques of organic compounds based on chromatographic techniques: A critical review

Analytical chemistry has increasingly focused on the environmental impact of its methods, with significant attention given to green principles in sample preparation. Techniques like Solid-Phase Microextraction (SPME), Micro-Solid-Phase Extraction (µ-SPE), Thin-Film Microextraction (TFME), Stir Bar Extraction (SBSE), Bar-Adsorptive Microextraction (BAµE), Disposable Pipette Extraction (DPX), and Rotative Disk Sorptive Extraction (RDSE) represent advancements in solid-phase extraction methods. Meanwhile, methods such as Single Drop Microextraction (SDME), Dispersive Liquid-Liquid Microextraction (DLLME), and Hollow Fiber Liquid-Phase Microextraction (HF-LPME) focus on liquid-phase techniques. Among the green approaches, biosorbents have gained prominence as extractor materials due to their environmental friendliness, renewability, biodegradability, and cost-effectiveness. In liquid-phase extractions, Natural Deep Eutectic Solvents (NADESs) have emerged as promising alternatives to traditional solvents. NADESs offer benefits such as biodegradability, biocompatibility, low toxicity, and affordability, along with ease of synthesis and purification. This review summarizes the application of NADESs and biopolymers, focusing in biosorbents, in microextraction and other techniques, based on literature from 2017 to the present. It is evident that NADESs present viable alternatives to conventional solvents, with their physical-chemical properties like viscosity, density, and polarity, being tunable through various mixtures. Similarly, biosorbents offer unique physicochemical properties that can outperform traditional commercial materials in sample preparation. Applications discussed in this review focus on the determination of organic compounds in environmental, food, and biological samples, utilizing chromatographic methods. These developments highlight the ongoing evolution in green analytical practices, aiming for more sustainable and efficient analytical procedures.

Spectrophotometric determination of o-phenylphenol in canned drinks using three-phase hollow-fiber liquid phase microextraction

A three-phase hollow-fiber liquid phase microextraction for o-phenylphenol (OPP) determination was developed. 1-octanol was employed as the organic phase, impregnated within the pores of the hollow fiber wall which was immersed in the sample solution, serving as a donor phase. OPP in the sample solution was extracted via octanol in the fiber pores into NaOH, which acted as the acceptor phase in the lumen of the fiber. The extracted OPP was then subjected to spectrophotometric detection at 712 nm using the indophenol blue reaction. The developed method showed a linear calibration curve (0.002–0.040 mg L−1) with high sensitivity (5.75 L mg−1), low limit of detection (0.31 μg L−1), and high recovery (73.6–94.8 %). Intra-day and inter-day precision at 2.1 μg L−1 OPP were 7.4 % (n = 12) and 10.9 % (n = 4) relative standard deviations, respectively. The determined OPP in various canned drinks was found to be between 2.0 and 17.8 μg L−1 using the developed method.

Combination of online hollow fiber liquid phase microextraction with smartphone-based sensing for in situ formaldehyde assay in fabric and wastewater samples.

A miniaturized analytical methodology was introduced based on the combination of a direct and online hollow fiber microextraction method with smartphone color detection. The method was used for the determination of formaldehyde (target analyte) in fabric and wastewater samples. In this regard, two reagents including ammonium acetate buffer and acetylacetone were added to the formaldehyde samples to create a colored compound. The colored compound was extracted from the sample by using the hollow fiber liquid-phase microextraction method, the extracted phase was not taken out of the extraction box and was directly transferred into a specially designed detection cell, and a smartphone was applied forin-situ color sensing and data readout. This combination gathered the advantages of both state-of-the-art microextraction techniques and smartphone sensing. Formaldehyde, as a carcinogenic compound widely used in paint and clothing industries, was selected as a model test. Factors affecting extraction efficiency were investigated and optimized, including the type of organic solvents, reagent concentration, salt, pH, stirring speed, reaction temperature, and extraction time. The linear region of the method under optimal conditions was 40-1500µg L-1 for wastewater samples and 0.3-11.2mg kg-1 for fabrics. The limit of detection and limit of qualification were 13 and 40µg L-1, respectively. The relative standard deviations for concentrations of 100 and 1000µg L-1 were 6% and 4%, respectively. To evaluate the application of the method for real samples, types of fabric and two samples of oil refinery wastewater were selected. The relative recovery in real samples was 84-98%. The results of the analytical parameters of the method show that the developed method can be used as an efficient method to determine formaldehyde in real samples.

Magnetic dispersive micro-solid-phase extraction integrated with hollow fiber liquid-phase microextraction for preconcentration of trace amounts of chlorpyrifos pesticide in aqueous samples

Magnetic dispersive micro-solid-phase extraction integrated with hollow fiber liquid-phase microextraction for preconcentration of trace amounts of chlorpyrifos pesticide in aqueous samples

The usability of green deep eutectic solvents in hollow fiber Liquid-Phase microextraction for the simultaneous extraction of analytes of different Natures: A comprehensive study

In the current study, a wide range of deep eutectic solvents (DESs) with different properties (hydrophilic, hydrophobic, ionic, and nonionic) were prepared in the initial phase. Subsequently, an assessment was conducted to evaluate some characteristics of the produced DESs, including their stability at room temperature and their capacity to extract three distinct types of analytes (anionic, cationic, and non-ionic) simultaneously through hollow fiber-liquid phase microextraction (HF-LPME) technique. To carry out the extraction procedure, the prepared DESs were inserted into the pores (as supported liquid membrane (SLM)) and lumen of hollow fiber membrane (HF) to apply two-phase and three-phase HF-LPME techniques. After a thorough evaluation, the three-phase HF-LPME technique (HF(3)-LPME) was chosen by using a mixture of menthol/TBAB-based hydrophobic DES (DES-35) as SLM and the mixture of malic acid/citric acid/water-based hydrophilic DES (DES-2) as an extraction solvent in the lumen of HF. All factors affecting the extraction recovery (including pH, extraction time, extraction temperature, stirring speed, and salt effect) were optimized utilizing the one-variable-at-a-time (OVAT) methodology. After applying the extraction procedure, all extracted samples were analyzed using the UV–Vis spectrometer and results were recorded at different wavelengths including 655 nm for Methylene blue, 550 nm for Amaranth, and 375 nm for Quercetin. The calibration graphs showed linearity in the range of 20.0–1500 µg/L, with a limit of detection of 6.2–15.1 µg/L and correlation coefficients higher than 0.9913 for the studied analytes. Moreover, the intra-day RSD, inter-day RSD, preconcentration factor (PF), enrichment factors (EF), and extraction recoveries (ER%) were obtained in the range of 3.1–4.8, 3.8–6.7, 125, 102.9–111.4, and 82.3–89.1 %, respectively. The use of the selected DES in the HF-LPME methodology resulted in an ecologically friendly strategy, as evidenced by the use of green metrics from the SPMS tool. The proposed strategy is also considered environmentally friendly due to its use of minimal solvents, waste reduction, and low energy consumption. The proposed technique effectively and simultaneously extractedmethylene blue, amaranth, and quercetin analytes in different real samples.

Statistical optimization of two-phase hollow fiber liquid-phase microextraction for preconcentration of strychnine in the clinical and postmortem biological fluids prior to gas chromatography-mass spectroscopy detection

Strychnine is a herbal alkaloid whose role in military and doping applications as well as the nervous system stimulation and cancer therapy has been confirmed. Because of its lethal nature, even at low dosages, developing a rapid, sensitive, and accurate method for determination of this alkaloid in the clinical and postmortem samples is of great importance. In this study, a green analytical method based on the two-phase hollow fiber liquid-phase microextraction (HF-LPME) combined with gas chromatography-mass spectrometry (GC–MS) was presented for preconcentration and determination of strychnine in biological fluids. A Box-Behnken design (BBD) with three variables, including extraction time (30–90 min), solution pH (9.0–11.0), and ionic strength (1.0–3.0 mol/L) was employed to maximize the extraction efficiency of strychnine by 1-octanol. The results were satisfactorily fitted to a quadratic response surface model (R2 = 0.979, F = 34.4) which predicted the optimum conditions of operation (extraction time of 89 min, pH = 11.0, and ionic strength of 3.0 mol/L). Based on the results, the studied variables and the interaction between pH and extraction time showed highly significant effects on the process efficiency. The calibration curve was linear in the concentration range of 2.7–1000.0 µg/L (R2 = 0.9978) and the limits of detection and quantitation were found to be 0.8 and 2.7 µg/L, respectively. Moreover, the method was successfully applied to different real samples, including urine (clinical sample), bile and stomach contents, blood, and vitreous humor (postmortem samples), and relative recoveries were obtained in the range of 93.8 % to 99.8 %. The findings of this study suggest that the environmentally friendly HF-LPME method which uses a small amount of a chlorine-free solvent, is a sensitive, cost-effective, simple, and efficient preconcentration method for trace determination of strychnine in biological fluids.

Development of a hollow fiber–liquid phase microextraction method using tissue culture oil for the extraction of free metoprolol from plasma samples

In this research, a method known as a hollow fiber-liquid-phase microextraction was employed to extract and concentrate free metoprolol from plasma samples. The extracted analyte was subsequently determined using high-performance liquid chromatography coupled with a diode-array detector. Several parameters, including hollow fiber length, sonication time, extraction temperature, and salt addition, were investigated and optimized to enhance extraction efficiency. After extracting the analyte under optimum conditions from plasma samples, the enrichment factor and extraction recovery were 50 and 86 %, respectively. Moreover, the method exhibited detection and quantification limits of 0.41 and 1.30 ng mL−1, respectively. The analysis of real samples demonstrated satisfactory relative recoveries in the range of 91–99 %.

Preconcentration of Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) in Clinical Samples by Various Hollow Fiber–Liquid Phase Microextraction (HF-LPME) Configurations With High-Performance Liquid Chromatography (HPLC) Detection

Hollow fiber liquid-phase microextraction is commonly used in analytical chemistry, providing high clean-up and pre-concentration factors. However, a major issue with this method is the long extraction time. The objective of this project is to reduce the extraction time by inducing different types of fluid motion in the sample solution. Three methods were employed: agitation using a magnetic stir bar in the horizontal position (conventional method), utilization of an air pump, and agitation using a magnetic stir bar in the vertical position for the pre-concentration and determination of non-steroidal anti-inflammatory drugs (naproxen, ibuprofen, and mefenamic acid) in biological samples via high-performance liquid chromatography with ultraviolet absorbance detection. The results demonstrated a significant reduction in extraction time and limit of detection when the air pump was employed compared to the conventional method of stirring with a magnetic stir bar in the horizontal position. Moreover, the mentioned parameters were even lower when stirring solutions were accomplished using a vertically-positioned magnetic stir bar, surpassing the method utilizing the air pump for agitation. Furthermore, the relative standard deviations were also lower when a vertically-positioned magnetic stir bar was used compared to the conventional method with a horizontally-positioned magnetic stir bar, while those of the air pump-assisted agitation method fell between the values of the aforementioned methods.

Hollow-fiber liquid phase microextraction for determination of fluoxetine in human serum by nano-liquid chromatography coupled to high resolution mass spectrometry

Therapeutic drug monitoring (TDM) is a personalized care tool based on the determination of a target drug concentration in human serum. An antidepressant drug of interest for such investigations is fluoxetine (FXT), due to a severe impact of genetic polymorphisms on its metabolism. A bioanalytical method employed for TDM purposes must exhibit satisfactory selectivity and detectability, which becomes more difficult due to highly complex biological matrices. In this study, a highly selective bioanalytical method for the determination of FXT in human serum is proposed, which provides excellent clean-up efficiency based on a low cost hollow fiber liquid-phase microextraction (HF-LPME) sample preparation step and nano-liquid chromatography coupled to high-resolution mass spectrometry (nano-LC-HRMS). HF-LPME was performed using a two-phase “U” configuration, with 6 cm fiber, 20 µL of 1-octanol acting as supported liquid membrane, and ammonium hydroxide (pH 10) as the donor phase with NaCl (10 % m/v) and methanol (5 % v/v) as additives, requiring only 250 µL of the sample. The procedure was conducted for 30 min under a 750 rpm stirring rate. Gradient elution was carried out employing an acetonitrile–water as mobile phase, the composition of 30:70 to 100:00 (v/v) for 15 min, using formic acid 0.1 % (v/v) as an additive. MS1 was acquired in an Orbitrap mass analyzer, while MS2 was acquired in a linear trap quadrupole. Satisfactory linearity (Pearson’s r = 0.99709) was obtained for a concentration range of 0.02 to 2.5 µg mL−1, which is compatible with the therapeutic and toxic range for FXT. The developed method presents adequate precision (1.61 to 7.45 %) and accuracy (95 to 114 %) and allows the dilution of high concentration samples in a 1:4 ratio (v/v), enabling its application for forensic serum samples. To our knowledge, this is the first study reporting a method based on HF-LPME and nano-LC-HRMS with any analytical purpose, especially with a TDM focus.

Efficient and recycled magnetic self-stirring hollow fiber-solid/liquid phase system: An extraction and removal technique for personal care pollutants

The removal of personal care products (PCPs) in aqueous environments is a huge challenge. Traditional powder and magnetic materials are not conducive to complete solid–liquid separation, which hinders their practical application. In this study, the convenient recyclable magnetic self-stirring system combining with n-octanol hollow fiber-liquid phase micro-extraction (HF-LPME), wormhole-like mesoporous carbon (WMC) solid phase and magnetic stirring was constructed to improve the extraction and removal efficiency of the trace PCPs (triclosan, triclocarban, 2, 2′-Dihydroxy-4-methoxybenzophenone, and 2, 4-dihydroxydiphenylketone) in wastewater. The adsorption process of triclosan and 2,2′-dihydroxy-4-methoxybenzophenone on the WMC surface followed the pseudo-first-order kinetics as well as Freundlich isotherm model. Because WMC had oxygen-containing groups and the multiple mesoporous distribution forming the n-octanol microextraction unit and the shearing strength generated by the stir bar in the water sample accelerated the mass transfer efficiency of PCPs, this system had the advantage of simultaneous removal and extraction of four PCPs from wastewater samples. The extraction mechanism involved the hydrophobic force and size effect between the WMC and PCPs. In addition, the factors affecting extraction efficiencies (EEs) were discussed, such as the concentrate of WMC (1 mg/L), rotation rate (400 rpm), extraction time (15 min), and salt concentration (30%). The results indicated that the method possessed a wide linear range (0.05–200 μg L-1), and lower limits of detection (LODs) (S/N = 3, 0.005–0.05 μg L−1), at the optimal conditions. This method also showed excellent reusability and stability, with higher recovery (88–98%) and fewer relative standard deviations (2.4–6.3%). This work not only minimized secondary pollution from powder adsorbents, but provided an economic and green magnetic self-stirring system and absorbent for the extraction, removal, and determination of typical PCPs pollutants from actual wastewater samples.

Supramolecular Solvent-Based Vortex-Assisted Hollow Fibre Liquid-Phase Microextraction Technique Combined With High Performance Liquid Chromatography for the Determination of Estrogens in Milk Samples

A fast, simple, environmental friendly and strong sample clean-up ability method for the determination of three estrogens (17β-estradiol (17β-E2), estrone (E1), and diethylstilbestrol (DES)) in milk samples has been developed by using supramolecular solvent-based vortex-assisted hollow fibre liquid-phase microextraction (SS-VA-HF-LPME) and high performance liquid chromatography. Method is based on estrogens was extracted from aqueous samples into a supramolecular solvent which were made up of n-octanol and ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM] BF4) impregnated in the wall pores and also filled inside the porous polypropylene hollow fiber membrane followed by vortex-mixing. The supramolecular solvent has better compatibility with the polarity of target analytes and the driving forces for the extraction include hydrogen bonding, hydrophobic and π-cation interactions between the analytes and the vesicular aggregates, thereby leading to high recoveries. Vortex can provide mild and effective mixing of sample solution and increase the contact between analytes and boundary layers of the hollow fibre. Therefore the mass transfer rate was enhanced. The parameters that affect the recoveries were studied and optimized. HF of 4 cm length was used and the pH 4.0 was employed. The percentages of n-octanol and [BMIM]BF4 were 10% and 3%, respectively. The extraction equilibrium time was 4 min. The method provided good linearity (andgt;0.998), repeatability (RSD% = 1.24–4.36), low detection limit (0.10–0.22 ng mL−1), and high enrichment factor (330).

Determination of pesticide residue in marginal lagoons of natural parks in Brazil using an improved calibrate passive sampler

Passive sampling is a sensitive and efficient method for analyzing pesticides in water. This article describes a hollow fiber liquid-phase microextraction (HF-LPME) device that was improved using polypropylene membranes grafted with nanocellulose for the passive sampling of pesticides in water. A comprehensive gas chromatography time-of-flight mass spectrometry (GCxGC/Q-TOFMS) system was used to separate, identify, and quantify pesticides. The sampling rates of 38 moderately hydrophobic to hydrophobic agricultural pesticides (2.18 < log Kow < 6.89) from different chemical classes, including the main triazine, organochlorine and organophosphate compounds, were calculated. A calibration process was applied to evaluate the role of flow velocity and select potential candidates for a possible performance reference compound (PRC). Sampling rates varied between 0.17 mL d−1 and 23.15 mL d−1. The accumulation curves identified linear periods ranging from 3 to 18 days. The new passive sampler device was applied for 8 days in rivers and marginal lagoons of natural parks of the São Francisco basin in Minas Gerais, Brazil and identified 10 target pesticides. Furthermore, 10 non-targeted pesticides were detected by the GCxGC/Q-TOFMS method.

Chemometrics optimization of an anionic carrier-mediated hollow fiber liquid-phase microextraction combined with HPLC-PAD for fluconazole extraction from plasma samples

In this research, we developed a method for fluconazole (FLU) quantification in plasma using carrier-mediated hollow fiber liquid-phase microextraction (HF-LPME). Briefly, the investigation of six solvents for fiber impregnation, two and three-phases modes of HF-LPME, and carrier-mediated HF-LPME were performed. A fractional factorial design 2(8–4) showed the influence of eight factors and it was followed by a central composite design with the most important three factors. Response surface and desirability test were also obtained. After optimization, the extraction condition consisted of the use of 500 µL of plasma samples containing FLU and 4.5 mL of NaOH solution (0.316 M) saturated with Na2SO4. Centrifugation was required for 15 min at 2200 g and 4 °C for sediment removal. A volume of 3.5 mL was transferred to extraction tubes and the fibers, already impregnated with 1-octanol and Adogen 464 (10 %), were placed in contact with the sample. Then, 60 µL of the acceptor phase were added inside the fiber, and stirring was performed at 1000 rpm for 40 min. Validation was performed in consonance with European Agency's Guideline on Bioanalytical Validation Methodology. The method showed linear range from 1.0 to 62.5 μg mL−1, recovery of 12 %, selectivity, no carryover effect, precision and accuracy within the recommended limits, and samples were stable in the stability studies performed. Finally, we confirmed the applicability of the obtained method at two samples obtained from a patient treated for neuromycosis with FLU. It is the first time that a microextraction technique is used for FLU analyses in plasma samples. The method showed good perspective of application in drug monitoring, without the need of large amounts of organic solvents that can be very harmful to health and environment.

Ultrasound-assisted three-phase hollow fiber microextraction-based method for untargeted metabolomics

Sample treatment for untargeted metabolomics is still the bottleneck of the analytical procedure, especially for complex samples like food or biofluids. The main pitfalls are the suppression of minor compounds, low metabolite coverage and the impossibility to detect certain families, combined with the requirement of non-selective approaches for untargeted analysis. Herein, we developed a new analytical extraction method for untargeted metabolomics using a non-selective procedure based on three phase hollow fiber liquid phase microextraction aided by ultrasound (three-phase-UA-HF-LPME) followed by gas chromatography-mass spectrometry. As a proof of concept, the method has been validated for human milk (HM). The analytical method allows extracting organic nitrogenous compounds from HM, which was not possible using the conventional liquid–liquid extraction (LLE) and provided cleaner chromatographic profiles and mass spectra with lower background noise. Moreover, three-phase-UA-HF-LPME enhanced the extraction of a high number of metabolites from 1.65 to 3.27-fold compared to LLE, namely: fatty acids and derivatives (decanoic acid, lauric acid, palmitic acid, tetradecanoic acid, palmitoleic acid, stearic acid, myristic acid, linoleic acid, azelaic acid), lipids and lipid-like molecules (oleamide, monopalmitin), organic acids and derivatives (lactic acid, citric acid), amino acids and peptides (glycine, proline, glutamine). Otherwise, the extraction of carbohydrates and derivatives (urea, phosphoric acid, galactose) decreased the fold changes from 0.15 to 0.25. Results show that our proposed method is attractive owing to its limits of detection from 0.08 to 0.16 mg L−1, recoveries of 99–86 %, enrichment factors up to 123 and fold changes very satisfactory when compared with LLE. The validation by targeted metabolomics as well as the untargeted procedure showed that three-phase-UA-HF-LPME presents better sensitivity, enrichment factors, sample throughput and metabolite coverage than the conventional LLE method considered the gold-standard for untargeted metabolomics. Our results show insights into the possible application of HF for untargeted metabolomics with important analytical advantages in comparison with the LLE.

Hydrophobic natural deep eutectic solvents based on L-menthol as supported liquid membrane for hollow fiber liquid-phase microextraction of triazines from water and urine samples

This work proposes the use of a hydrophobic natural deep eutectic solvent (NADES) as a supported liquid membrane (SLM) for hollow fiber liquid phase microextraction (HF-LPME) of triazines. NADES were prepared using L-menthol as hydrogen bond acceptor combined with different hydrogen bond donors of natural origin: carboxlylic acids, alcohols and amines. Studies were carried out to determine whether the prepared NADES met the necessary requirements to be used as a SLM, such as stability in the HF and compatibility with HPLC. Then, the ability of each prepared NADES to extract 6 triazine herbicides by HF-LPME from aqueous samples was evaluated. Among them, the mixture L-menthol: formic acid (molar ratio 1:2) provided better extraction results and was selected as SLM. The influence the different parameters on extraction efficiency such as pH of both sample and acceptor solution, salting-out effect, extraction time and stirring rate on the extraction efficiency was carefully studied and optimized. The optimized HF-LPME procedure was applied to the analysis of aqueous samples such as artificial water containing humic acids, tap water, river water and urine, with excellent clean-up ability for all samples analyzed. Relative recoveries ranged from 68 to 128 %, and the LODs and LOQs obtained for the 6 triazines were 0.75–3.1 µg/L and 2.5–10.3 µg/L, respectively, depending on the analyte and the kind of sample. Additionally, according to the AGREEprep tool assessment, the proposed method appears as a greener approach compared to other microextraction methods reported in the literature for the analysis of triazines in water samples.

Deep eutectic solvents in sample preparation and determination methods of pesticides: Recent advances and future prospects

This review summarizes recent advances of deep eutectic solvents (DESs) in sample preparation and determination methods of pesticides in food, environmental, and biological matrices since 2019. Emphasis is placed on new DES categories and emerging microextraction techniques. The former incorporate hydrophobic deep eutectic solvents, magnetic deep eutectic solvents, and responsive switchable deep eutectic solvents, while the latter mainly include dispersive liquid-liquid microextraction, liquid-liquid microextraction based on in-situ formation/decomposition of DESs, single drop microextraction, hollow fiber-liquid phase microextraction, and solid-phase microextraction. The principles, applications, advantages, and limitations of these microextraction techniques are presented. Besides, the use of DESs in chromatographic separation, electrochemical biosensors, fluorescent sensors, and surface-enhanced Raman spectroscopy are discussed. This review is expected to provide a valuable reference for extracting and detecting pesticides or other hazardous contaminants in the future.

Hierarchical porous zeolitic imidazolate framework‑8 supported hollow-fiber liquid-phase microextraction of nine typical phenolic pollutants in water samples followed by electrophoretic analysis

Hierarchical porous zeolitic imidazolate framework‑8 (HpZIF-8) have not only good chemical and thermal stability, but also pore structures of different sizes. In this work, HpZIF-8 supported hollow-fiber liquid-phase microextraction (HpZIF-8@HF-LPME) co-modified with tributyl phosphate and 2-nitroethyl benzene was firstly developed for purification and enrichment of nine typical phenolic pollutants followed by electrophoretic separation and amperometric detection (CE-AD). The key enrichment parameters were optimized by full factorial experimental and central composite designs. Under the optimum conditions, the maximum enrichment factors for the nine analytes were 479 (phenol), 249 (2-chlorophenol), 821 (4-chlorophenol), 1253 (3-methylphenol), 1376 (2,4-dichlorophenol), 1078 (2,4,6-trichlorophenol), 200 (pentachlorophenol), 614 (4-nitrophenol) and1827 times (bisphenol A), respectively. The limits of detection were 0.060-1.5µg L-1 (S/N=3) in real sample matrixes. This proposed method has been successfully applied to water samples with high ionic strength, and the average recoveries were in the range of 80.2-118.0%. This developed method of HpZIF-8@HF-LPME/CE-AD needs no desorption and derivatization, providing an alternative for monitoring typical phenolic pollutants in water samples.

Determination of three plant growth regulators in Dendrobium officinale and Anoectochilus roxburghii by three-phase hollow fiber liquid phase microextraction- high performance liquid chromatography

Dendrobium officinale (D. officinale) and Anoectochilus roxburghii (A. roxburghii) are precious raw materials for traditional Chinese medicine. The growing demand for D. officinale and A. roxburghii cannot be met by current production techniques. Hence, the widespread artificial cultivation of D. officinale and A. roxburghii using substantial amounts of plant growth regulators (PGRs) has emerged. The excessive use of PGRs not only affects the quality and efficacy of medicinal materials but also causes a series of safety issues. Therefore, expanding research on residual PGRs in valuable Chinese medicinal materials is important to avoid the health hazards caused by these substances. Unfortunately, the identification of PGRs is challenging because of their trace and complex matrices. High performance liquid chromatography (HPLC) has become one of the mainstream analytical methods for PGR determination. An important consideration in the application of this technique to the detection of trace acidic PGRs is how to improve its accuracy and sensitivity. Three-phase hollow fiber liquid phase microextraction (3P-HF-LPME) has the advantages of a high enrichment factor, complex sample purification ability, low reagent consumption, low cost, and easy integration with chromatographic systems. Thus, the 3P-HF-LPME method overcomes the many shortcomings of traditional sample pretreatment methods. In this study, a novel, simple, and effective analytical method based on 3P-HF-LPME combined with HPLC was developed to extract, purify, enrich, and detect three trace acidic PGRs (indole-3-acetic acid, naphthyl acetic acid and indolebutyric acid) in D. officinale and A. roxburghii. The chromatographic separation conditions and 3P-HF-LPME model parameters were systematically optimized for this purpose. First, the sample solution was prepared by ultrasonication and low-temperature standing, and then adjusted to pH 3.0 using dilute hydrochloric acid. The sample solution (10 mL) and NaCl (1.50 g) were stored in a 15 mL brown extraction bottle with a built-in magnetic stirrer. Next, 30 μL of NaOH solution (pH 11.0) as the inner phase solution was injected into the inner cavity of a hollow fiber tube, which was subsequently sealed at both ends. The hollow fiber tube was soaked in n-octanol for 5 min and dried naturally to remove excess extraction solvent from its surface. Finally, the fiber tube was placed in a brown extraction bottle and stirred using a thermostatic magnetic stirrer at 40 ℃ and 1600 r/min for 2 h. After extraction, the three target analytes were separated on a Welch Ultimate XB-C18 column (250 mm×4.6 mm, 5 μm) under isocratic elution conditions using acetic acid aqueous solution and methanol (45∶55, v/v) as the eluent. The results indicated that the three PGRs showed good linearity in the range of 0.5-100.0 μg/L (coefficients of determination (r2)=0.9999), with limits of detection (LODs) of 0.02-0.15 μg/L. The method recoveries were 88.5-102.2%, with relative standard deviations (RSDs) of less than 3.7% (n=3). The extraction efficiencies and enrichment factors of the three PGRs in 15 batches of fresh D. officinale and A. roxburghii products were found to be 42.0%-86.8% and 140-289. Full-scan mass spectrometry was used to further identify positive samples to avoid false-positive results and enhance the reliability of the experimental method. In summary, the proposed method is sensitive, accurate, reliable, environment friendly, and capable of high enrichment. It could be used to determine the residues of three acidic PGRs in D. officinale and A. roxburghii. Moreover, it can provide technical support for the residue detection of PGRs in other Chinese medicinal materials.