Advances and Applications of Hybrid Graphene-Based Materials as Sorbents for Solid Phase Microextraction Techniques.

The advancement of traditional sample preparation techniques has brought about miniaturization systems designed to scale down conventional methods and advocate for environmentally friendly analytical approaches. Although often referred to as green analytical strategies, the effectiveness of these methods is intricately linked to the properties of the sorbent utilized. Moreover, to fully embrace implementing these methods, it is crucial to innovate and develop new sorbent or solid phases that enhance the adaptability of miniaturized techniques across various matrices and analytes. Graphene-based materials exhibit remarkable versatility and modification potential, making them ideal sorbents for miniaturized strategies due to their high surface area and functional groups. Their notable adsorption capability and alignment with green synthesis approaches, such as bio-based graphene materials, enable the use of less sorbent and the creation of biodegradable materials, enhancing their eco-friendly aspects towards green analytical practices. Therefore, this study provides an overview of different types of hybrid graphene-based materials as well as their applications in crucial miniaturized techniques, focusing on offline methodologies such as stir bar sorptive extraction (SBSE), microextraction by packed sorbent (MEPS), pipette-tip solid-phase extraction (PT-SPE), disposable pipette extraction (DPX), dispersive micro-solid-phase extraction (d-µ-SPE), and magnetic solid-phase extraction (MSPE).

Pipette-tip solid-phase extraction coupled with matrix-assisted laser desorption/ionization mass spectrometry enables rapid and high-throughput analysis of antidepressants in rat serum.

Therapeutic drug monitoring is essential for ensuring the efficacy and safety of medications. This study introduces a streamlined approach that combines pipette-tip solid-phase extraction (PT-SPE) with matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS), facilitating rapid and high-throughput monitoring of drug concentrations. As a demonstration, this method was applied to the extraction and quantification of antidepressants in serum. Utilizing Zip-Tip C18, the method enabled the extraction of antidepressants from complex biological matrices in less than 2 min, with the subsequent MALDI-MS analysis yielding results in just 1 min. Optimal extraction recoveries were achieved using a sampling solution at pH 9.0 and a 10 µL ethanol desorption solution containing 0.1% phosphoric acid. For MALDI analysis, 2,5-dihydroxybenzoic acid was identified as the most effective matrix for producing the highest signal intensity. The quantification strategy exhibited robust linearities (R2 ≥ 0.997) and satisfactory limits of quantification, ranging from 0.05 to 0.5 µg/mL for a suite of antidepressants. The application for monitoring dynamic concentration changes of antidepressants in rat serum emphasized the method's efficacy. This strategy offers the advantages of high throughput, minimal sample usage, environmental sustainability, and simplicity, providing ideas and a reference basis for the subsequent development of methods for therapeutic drug monitoring.

Mechanochemical synthesis ionic covalent organic frameworks/cotton composites for pipette tip solid-phase extraction of domoic acid in seafood.

Pipette tip solid-phase extraction (PT-SPE) as a miniaturized solid-phase extraction technique have a wide range of applications in the field of sample pretreatment. In this study, ionic covalent organic frameworks@cotton (iCOF@cotton) were facilely synthesized by mechanochemical grinding method only in half an hour, and used as the adsorbents of PT-SPE. The synthesized iCOF@cotton not only had high specific surface area, suitable pore structure and cationic charge groups of iCOF that can extract polar targets quickly, but also reduced the problem of high back pressure of PT-SPE by the addition of cotton, thus accelerating extraction time. Combined with high performance liquid chromatographic tandem mass spectrometry (HPLC-MS/MS), an efficient and sensitive method was established for detection of domoic acid (DA, a toxin produced by algae). Under the optimal conditions, the proposed analysis method displayed excellent analytical performance, including broad range of linearity (10-1000 pg mL-1), low limit of detection (LOD, 5 pg mL-1), high correlation coefficient (0.9993), satisfactory precision (RSDs ≤6.4 %). In addition, the developed method was applied to the detection of DA in marine samples, and detected trace DA (18.6 pg mL-1) with satisfactory recovery (85.7%-107.2 %). The above results indicated that the prepared iCOF@cotton have great potential as the adsorbents for PT-SPE.

Determination of alectinib and its active metabolite in plasma by pipette-tip solid-phase extraction using porous polydopamine graphene oxide adsorbent coupled with high-performance liquid chromatography-ultraviolet detection.

Alectinib is known as an effective targeted drug, which has excellent therapeutic effect on non-small cell lung cancer and can significantly prolong the survival of patients. Therapeutic drug monitoring is necessary due to the photo-instability of alectinib and the individual differences in patients. In this work, a porous polydopamine graphene oxide composite (PDAG) was prepared by a simple surface modification method. A PDAG-based pipette-tip solid-phase extraction (PT-SPE) coupled with HPLC-UV detection was proposed for the separation and detection of alectinib and its active metabolite M4 in plasma. The method was methodologically validated and showed good linearity in the range of 50-5000 ng mL-1 (R2 > 0.9995). The limit of detection (LOD) was 4.8 ng mL-1 and 3.9 ng mL-1 for alectinib and M4, respectively, and the limit of quantitation (LOQ) was 16.1 ng mL-1 and 13.1 ng mL-1, respectively. The intra-day and inter-day precision expressed by coefficient of variation was less than 4.8 %. The recovery of this method ranged from 84.9 % to 103.5 % with a standard deviation of less than 4.3 %. In conclusion, the established method is accurate, stable and inexpensive, and can be used to monitor the levels of alectinib and M4 in plasma, which provide technical and data support for exploring optimal individualized remedial dosing regimens.

Simultaneous determination of three biomarkers of non-small cells lung cancer in urine by pipette-tip solid-phase extraction coupled with liquid chromatography tandem mass spectrometry.

Simultaneous determination of multiple biomarkers can improve the effectiveness and accuracy of cancer diagnosis. Cortisol, cortisone, and 4-methoxyphenylacetic acid (4-Me) are metabolic biomarker group with high specificity and sensitivity for the diagnosis of non-small cells lung cancer (NSCLC), and the development of their simultaneous determination method is desired. Herein, a simple, sensitive, and low-cost method involving pipette-tip solid-phase extraction (PT-SPE) using anion exchange adsorbent (MAX) coupled with liquid chromatography tandem mass spectrometry (LC-MS/MS) was developed for the simultaneous determination of three biomarkers (cortisol, cortisone, and 4-Me) in human urine. The sample (0.1 mL), adsorbent (1.5 mg) and organic reagent (3.5 mL) of MAX-PT-SPE are less consumed, and have the advantages of easy access to raw materials, simple assembly, convenient on-site instant extraction, low pollution, and low cost. The limits of detection of the three biomarkers were 0.006-0.024 ng mL-1, the recoveries of three spiked levels (2, 50, and 500 ng mL-1) were 91.0%-99.3%, with the relative standard deviations (RSDs) ≤ 5.9%. Finally, the MAX-PT-SPE-LC-MS/MS method achieved the quantitative analysis of cortisol, cortisone, and 4-Me in urine of different patients of NSCLC. This method is expected to be used in the non-invasive auxiliary diagnosis of NSCLC, and it provides a new strategy for multi-molecular diagnosis and multi-omics combined diagnosis.

Metal-organic frameworks modified melamine foam in pipette-tip for rapid solid-phase extraction of organophosphorus pesticides in fruits and vegetables.

In this work, metal-organic frameworks (MOFs) including Fe-MIL-101 and Ti-MIL-125 were prepared and fixed on the melamine foam (MF) by polyvinylidene fluoride (PVDF) to prepare MF/PVDF/MOFs, which was used as adsorbents in pipette-tip solid-phase extraction (PT-SPE) for rapid extraction of organophosphorus pesticides (OPPs). Then, a gas chromatograph-flame thermionic detector (GC-FTD) was used for simultaneous analysis of Dimethoate (DMT), Iprobenfos (IBF), Parathion-methyl (PAM), and Chlorpyrifos (CPF). The morphology, crystal structure, and functional groups of MF/PVDF/MOFs were characterized, indicating that Ti-MIL-125 and Fe-MIL-101 were successfully synthesized and distributed on MF. The Fe-MIL-101 and Ti-MIL-125 showed good extraction ability for OPPs, which was mainly due to the π-π interaction and the multiple porous structures. Under the optimal conditions, the limit of detection (LODs) of four OPPs was 0.03-0.14 µg L-1 and the RSDs were less than 9.9%. The developed PT-SPE method showed a short extraction time (<3 min). The recoveries in fruits and vegetables (Celery, cabbages, and oranges) ranged from 75.3%-118.8% (RSDs<9.6%). The prepared MF/PVDF/MOFs demonstrated the efficient extraction performance of OPPs, contributing to the rapid pretreatment of OPPs from food and the environment.

Synthesis of azo-linked covalent organic polymers for pipette tip solid-phase extraction of sedative residues from animal tissues samples.

Azo-linked covalent organic polymers (ACOPs) were synthesized by a simple azo reaction, with 2,2'-bis(trifluoromethyl)benzidine and 1,3,5-trihydroxybenzene as the monomers. The preparation process was mild, green, and environmental-friendly, avoiding the use of high temperature, metal catalysis, and harmful organic reagent. The obtained ACOPs were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, powder X-ray diffraction, and Brunauer-Emmett-Teller. With the prepared ACOPs as adsorbent, a method of pipette tip solid-phase extraction-liquid chromatography-tandem mass spectrometry detection (PTSPE-LC-MS/MS) was proposed for the analysis of target sedatives in animal tissues. Furthermore, the parameters for the extraction of five sedatives, including the amount of adsorbent, pH value, ion strength, elution solvent and volume, were investigated. Under the optimized conditions, the linear dynamic range was found from 0.1 to 10.0 µg kg-1, and the limits of detection were ranged from 0.02 to 0.1 µg kg-1. The method was assessed by the analysis of target sedatives in animal tissues, and the recoveries for the spiked pork muscle and pork liver samples were 84-102% and 83-101%, respectively. The results show that the developed method of PTSPE-LC-MS/MS with ACOPs as adsorbent is efficient for the analysis of trace sedatives in animal tissues.

A molecularly imprinted polymer monolithic column with dual template and bifunctional monomers for selective extraction and simultaneous determination of eight phenolics from polycarbonate cups.

A molecularly imprinted polymer (MIP) monolithic column was prepared in situ in a pipette tip using phenol and bisphenol A as dual templates, 4-vinyl pyridine and ß-cyclodextrin as bifunctional monomers. It was used for the selective and simultaneous solid phase extraction of eight phenolics, including phenol, m-cresol, p-tert-butylphenol, bisphenol A, bisphenol B, bisphenol E, bisphenol Z, and bisphenol AP. The MIP monolithic column was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis and nitrogen adsorption experiment. The results of selective adsorption experiments showed that the MIP monolithic column can selective recognize the phenolics and have excellent adsorption property. The imprinting factor for bisphenol A can be as high as 4.31, and the maximum adsorption capacity for bisphenol Z can reach 201.66 mg g-1. Under the optimal extraction conditions, a selective and simultaneous extraction and determination method for eight phenolics was established based on the MIP monolithic column and high-performance liquid chromatography with ultraviolet detection. The linear ranges (LRs) of the eight phenolics were 0.5-200 µg L-1, the limits of quantification (LOQs) and detection (LODs) were 0.5-2.0 µg L-1 and 0.15-0.67 µg L-1. The method was applied to detect the migration quantity of the eight phenolics from polycarbonate cups and had satisfactory recovery. The method has the advantages of simple synthesis, short extraction time, as well as good repeatability and reproducibility, which provides a sensitive and reliable strategy for extracting and detecting phenolics from food contact material.

Electrospun fluorinated carbon nanotubes/silk fibroin composite nanofibers for the analysis of perfluoroalkyl and polyfluoroalkyl substances.

Assessment of the exposure risk of perfluoroalkyl and polyfluoroalkyl substances (PFASs) has been of public concern for many years. However, it is a challenging undertaking because of the trace levels of these contaminants in the environment and biological systems. In this work, fluorinated carbon nanotubes/silk fibroin (F-CNTs/SF) nanofibers were for the first time synthesized by electrospinning and evaluated as a new adsorbent in pipette tip-solid-phase extraction to enrich PFASs. The addition of F-CNTs increased the mechanical strength and toughness of the SF nanofibers, thus improving the durability of composite nanofibers. The proteophilicity of silk fibroin formed the basis of the good affinity of this material with PFASs. The adsorption behaviors of PFASs on the F-CNTs/SF were investigated by adsorption isotherm experiments to understand the mechanism of extraction. With analysis using ultrahigh performance liquid chromatography-Orbitrap high-resolution mass spectrometric, low limits of detection (0.006-0.090 µg L-1) and enrichment factors of 13-48 were obtained. Meanwhile, the developed method was successfully applied to the detection of wastewater and human placenta samples. This work provides a new idea for the design of novel adsorbents with proteins integrated in polymer nanostructures, a potential routine and practical monitoring technique for PFASs in environmental and biological samples.

Novel covalent organic frameworks based electrospun composite nanofiber membranes as pipette-tip strong anion exchange sorbent for determination of inorganic arsenic in rice.

Novel covalent organic frameworks (COFs) based PAN@TpBD(NH2)2 electrospun composite nanofiber membranes (ECNMs) were fabricated as strong anion exchange sorbent by implementing electrospinning technology. The finished sorbent was characterized, and key parameters of pipette-tip solid phase extraction (PTSPE) procedures were investigated. Inorganic arsenic (iAs) was successfully separated from rice under the optimal precondition conditions, and quantified by hydride generation-atomic fluorescence spectrometry (HG-AFS). This PTSPE-HG-AFS methodology achieved 0.015 µg L-1 detection limit, 4.67 % relative standard deviation, and 86.48～99.11 % recoveries. In this work, preparation and characterization of this novel COFs-based anion exchange sorbent, PAN@TpBD(NH2)2 ECNMs, is described and its suitability for PTSPE applications is demonstrated.

Miniaturized extraction and determination of swelling agents in fruits and vegetables based on deep eutectic solvent-molecularly imprinted hydrophilic resin.

The overuse of swelling agents in fruits and vegetables has rapidly increased, resulting in food safety problems. Hence, a new method for the selective extraction and detection of thidiazuron (TDZ) and forchlorfenuron (KT30) was developed using deep eutectic solvent-molecularly imprinted hydrophilic resin (DES-MIHR) as a pipette tip solid-phase extraction (PT-SPE) adsorbent with excellent molecular recognition in aqueous matrixes. DES-MIHR interacted with TDZ and KT30 via π-π interactions and hydrogen bonding. The miniaturized PT-SPE can be performed with just 5.0 mg adsorbent, 0.3 mL water, and 0.2 mL eluent, thus having the advantage of the low consumption of adsorbent and organic reagents. The performance of the DES-MIHR-PT-SPE-high-performance liquid chromatography (HPLC) method was demonstrated with the recoveries from various fruits and vegetables being 81.1-102.9 % (RSD ≤ 7.1 %). Thereby indicating the general applicability of the developed method for the accurate determination of trace swelling agents in fruits and vegetables.

Triazine-based porous organic polymer as pipette tip solid-phase extraction adsorbent coupled with HPLC for the determination of sulfonamide residues in food samples.

In this work, triazine-based porous organic polymer (TAPT-BPDA) synthesized by simple solvothermal method with stable chemical properties was employed as pipette tip solid-phase extraction (PT-SPE) adsorbent for the extraction of sulfonamides for the first time. Under the optimal conditions, good linearities (1-300 µg L-1, R2 ≥ 0.9987) and low limits of detection (0.10-0.28 µg L-1) were obtained. The recoveries of sulfonamides in meat, egg and milk samples were in the range of 76.1-114.0 %. The prepared TAPT-BPDA showed good reusability with the recoveries of sulfonamides remained above 80.0 % after eight recycles. The adsorption mechanism between SAs and adsorbent might be the combined effects of electrostatic interactions, hydrogen bonding and π-π interactions. The results demonstrated potential applications of a TAPT-BPDA-based PT-SPE-HPLC method for the analysis of trace sulfonamide residues in food samples.

Preparation and evaluation of a chitosan modified biochar as an efficient adsorbent for pipette tip-solid phase extraction of triazine herbicides from rice.

The low allowable limit of triazine herbicides (THs) in rice makes it imperative to develop novel sample pretreatment methods for extraction and preconcentration of THs. Herein, a phosphoric acid activated biochar (PBC) was prepared and modified by chitosan (CS). For THs with different polarities, CS-PBC with multiple interaction sites exhibited satisfactory chemisorption. On this basis, a CS-PBC-based pipette tip-solid phase extraction (PT-SPE) was developed combined with HPLC to extract THs from rice. Low limits of detection (1.41-3.35 ng g-1), satisfactory linearity (0.01-2.00 µg g-1, R2 > 0.9974) and recoveries (96.13-116.25 %) were obtained with acceptable inter-day and intra-day precision (RSD ≤ 13.60 %). CS-PBC showed superior performance to three commercial single-mode adsorbents and comparable results to a hydrophilic-lipophilic balance adsorbent. The study explored the feasibility of PT-SPE for extracting THs from rice and broadened the application of plant biochar as an environmentally-friendly matrix in food sample pretreatment.

Green synthesis of phloroglucinol-urotropine porous polymer: Ingenious miniaturized solid phase extraction for efficient purification and determination of polycyclic aromatic hydrocarbons in lotus roots.

Polycyclic aromatic hydrocarbons (PAHs) posed a serious threat to food safety and human health due to long-term emission. In this work, a new method was established using phloroglucinol-urotropine porous polymer (PU-PP) in a pipette tip for solid phase extraction (PT-SPE) for the first time and used prior to determination of four PAHs (phenanthrene, anthracene, fluoranthene, and pyrene) in lotus roots. Synthesis of the PU-PP adsorbent was green compared with alternatives; urotropine was used as a cross-linker and ethanol-water as the solvent. PU-PP-based PT-SPE had the advantages of low solvent consumption, good purification, practicability, stability, and low-cost. The proposed pre-purification method offered low limits of detection (0.09-0.28 ng/g) and good recoveries (84.6-114.3 %, RSDs ≤ 5.6 %) for determination of the four PAHs, which were detected at trace concentrations in samples. This new method provides an alternative for monitoring trace pollutants in aquatic plant ingredients.

Peanut shells-derived biochars as adsorbents for the pipette-tip solid-phase extraction of endocrine-disrupting phenols in water, milk and beverage.

In the present work, a type of biochar materials derived from carbonizing peanut shells were obtained and employed as the adsorbents of pipette-tip solid-phase extraction (PT-SPE) for the enrichment and determination of six endocrine-disrupting phenols (EDPs) in combination with high-performance liquid chromatography equipped with ultraviolet detector (HPLC-UV). Abundant aliphatic and aromatic carbon structures and functional groups from polar heteroatoms (N, O, S) were distributed in the low-cost and eco-friendly peanut shells-derived biochar materials and were favorable for the enrichment of target EDPs. Moreover, the theoretical calculation based on density functional theory (DFT) proved that the effective enrichment of EDPs in aqueous samples benefited from the effective adsorption on the peanut shells-derived biochar materials. The experimental factors influencing the extraction efficiency were investigated, including adsorbent amount, aspirating/dispensing cycles, the type of elution solvent and elution times, salt addition, sample solution pH and type and volume of washing solvent. Under the optimal conditions, the proposed PT-SPE method exhibited good linear relationship (R2 > 0.993) in the range of 0.5-400 µg/L and low limits of detections (LODs) from 0.25 to 2.5 µg/L, as well as good precision and accuracy with relative standard deviations (RSDs) of 0.3%-13.2% and recoveries of 83.5%-117.1%. Finally, the biochars-based miniaturized pretreatment method was employed for the determination of six EDPs in bottled water, milk, tea beverage and disposal plastic bag soaked solution with recoveries from 77.5% to 116.5%.

Disposable pipette extraction: A critical review of concepts, applications, and directions.

Analytical chemistry has always been evolving towards techniques that are increasingly simple and effective and that conform to green principles. Disposable pipette extraction (DPX, also known as dispersive pipette tip solid phase extraction) is a recent technique that has become an interesting tool in sample preparation methodologies. The principle is based on a dynamic mixture between the matrix and the sorbent which allows rapid and effective extraction of analytes and provides vigorous clean-up of the samples. In the context of fitting in with green chemistry, DPX has contributed to replacing commercially available materials with natural alternative materials. The production of these materials is also simple, reduces sample/solvent volumes, consequently generates less waste and is less laborious and safer for the laboratory worker. This review is a source of information about the DPX technique, dealing with its basic concepts, procedure, optimizations, materials for the main applications published so far, which are in the food, environmental and biological (forensic) sciences.

Rapid determination of antiviral drugs in yellow catfish (Pelteobagrus fulvidraco) using graphene/silica nanospheres (G/KCC-1) based pipette tip solid-phase extraction with ultra-performance liquid chromatography-tandem mass spectrometry.

Yellow catfish (Pelteobagrus fulvidraco) is commonly contaminated by protease inhibitors because of the illegal use of antiviral drugs in aquaculture, so the determination of antiviral drugs is essential in food safety supervision. In this study, a novel sorbent, graphene and silica nanospheres composite (G/KCC-1), was synthesized for pipette-tip-based solid-phase extraction (PT-SPE) and purification of ritonavir, saquinavir, and indinavir in yellow catfish, followed by ultra-performance liquid chromatography and tandem mass spectrometry (UPLC-MS/MS) analysis. The wrinkly structure of G/KCC-1 with center-radial nanowrinkles enlarged the surface area and increased the capacity of absorbing the target analyte. With the proposed G/KCC-1 based PT-SPE UPLC-MS/MS method, the pH of sample solution, aspirating/dispensing cycles for extraction and elution were optimized to be 4.0, 25, and 10 respectively, and the eluting solvent was methanol/ammonia (95:5, v/v) with 0.02 M sodium chloride. This new method was further validated to be linear (correlation coefficient R2, 0.9993-0.9996), sensitive (limit of detection, LOD ≤ 0.8 ng mL-1), accurate (89.3-114.2%), and precise (relative standard deviation, RSD ≤ 6.23%). These results indicated that the proposed method is qualified in bioanalytical method validation and meets the requirements for detecting illegally used antiviral drugs in yellow catfish. The demonstrated G/KCC-1 based PT-SPE UPLC-MS/MS method is a potential analytical method in food and drug administration.

Combination of pipette tip solid phase extraction and high performance liquid chromatography for determination of plant growth regulators in food samples based on the electrospun covalent organic framework/polyacrylonitrile nanofiber as highly efficient sorbent.

Facile and sensitive determination of plant growth regulators (PGRs) in food samples is important but still remains great challenge. Herein, a pipette tip solid phase extraction (PT-SPE) method was developed for fast and sensitively detecting PGRs. The PT-SPE adsorbent was prepared by integrating a novel covalent organic framework (COF) of schiff base network 3 (SNW-3) and polyacrylonitrile (PAN) through electrospinning. The SNW-3 can easily adsorb PGRs with high special affinity through electrovalent bands between the ammonium ions of SNW-3 and the carboxy groups of PGRs. The polymer of PAN acts as scaffold material for SNW-3, which can lower seepage pressure hence accelerates adsorption/desorption kinetics. By combination with HPLC-DAD, a satisfactory method was successfully developed for simultaneous determination of ten PGRs in watermelon. Good analytical performances were achieved with this proposed method, including good linearity (5-500 ng/mL) with high correlation coefficients (R ≥ 0.9981), low limits of detection (S/N = 3, 0.24-3.19 ng/mL) and limits of quantification (S/N = 10, 1.65-5.72 ng/mL), satisfactory precision (intra-day RSDs ≤ 2.7%, inter-day RSDs ≤ 3.7%), and high accuracy (recovery: 82.8-113.0%). The method developed in this study shows high potential for design of high target-affinity adsorbents for food sample preparing.

Macro-microporous zeolitic imidazole framework-8/cellulose aerogel for semi-automated pipette tip solid phase extraction of fluoroquinolones in water.

In this study, Zeolitic Imidazole Framework-8/cellulose aerogel (ZIF-8/CA) hybrid was successfully fabricated through a simple doping method and ZIF-8 acted as the major component for adsorption. In order to elucidate the adsorption mechanism deeply, molecular simulation was adopted to the expound the interaction modes between ZIF-8 and the fluoroquinolones (FQs). ZIF-8/CA was used as the adsorbent for semi-automated pipette tip solid phase extraction (PT-SPE). In combination with high performance liquid chromatography tandem fluorescence detector (HPLC-FLD), the established method was successfully employed to determine trace amount of FQs in water samples. Extraction parameters such as the content of ZIF-8, pH of sample solution, volume of sample, flow rate of sampling, type and volume of elution solvent were investigated. Under the optimized conditions, satisfactory linearity was achieved with the correlation coefficient (R2) ranging from 0.9954 to 0.9992. The limits of detection were in the range of 0.337-1.707 ng L-1. And the recoveries varied from 75.9% to 96.8% with RSD less than 8.0%. The established method was demonstrated to be sensitive, efficient and convenient.

Simultaneous trace-level monitoring of seven opioid analgesic drugs in biological samples by pipette-tip micro solid phase extraction based on PVA-PAA/CNT-CNC composite nanofibers followed by HPLC-UV analysis.

Electrospun poly(vinyl alcohol)-(PVA)-poly(acrylic acid) (PAA)/carbon nanotubes(CNTs)-cellulose nanocrystal (CNC) (PVA-PAA/CNT-CNC) composite nanofibers were prepared and characterized using Fourier transform-infrared spectroscopy and field emission scanning electron microscopy. The resultant composite was used as an effective and novel sorbent for pipette-tip micro-solid phase extraction (PT-µSPE) of seven opioid analgesics (OAs) in biological samples followed by HPLC-UV analysis. Addition of CNT-CNC with the high specific surface area and plenty of OH-functional groups endows the nanofibers with considerable extraction efficiency. Under the optimum conditions, the linearity was obtained in the range 1.5 to 700.0 ng mL-1 for morphine, codeine, oxycodone, and tramadol, and 0.5 to 1000.0 ng mL-1 for nalbuphine, thebaine, and noscapine with coefficient of determination (r2) ≥ 0.9990. Detection limits (LODs) based on S/N = 3 were in the range of 0.15-0.50 ng mL-1. The relative standard deviations (RSDs) of 4.1-5.4% (intra-day, n = 5) and 5.2-6.4% (inter-day, n = 3) for three consecutive days were achieved. Finally, the efficiency of the PT-µSPE-HPLC-UV method was evaluated for the determination of OAs in human plasma and urine samples with good recoveries (87.3 to 97.8%). A: Schematic illustration for the preparation of PVA-PAA/CNT-CNC composite nanofibers. B: Schematic presentation of applying PVA-PAA/CNT-CNC composite nanofibers as the sorbent in pipette-tip micro solid-phase extraction (PT-µSPE) for the preconcentration of seven opioid analgesic drugs in biological samples before HPLC-UV analysis.