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).

Determination of amphetamines in hair samples using microextraction by packed sorbent and gas chromatography-mass spectrometry.

Several protocols for the analysis of amphetamine-type stimulants (ATS) in hair have been developed over the years, with microextraction by packed sorbent (MEPS) being used for drugs like opiates, cocaine and ketamine. However, concerning ATS determination in hair samples, this approach has only been applied so far to amphetamine (AMP) and methamphetamine (MAMP). This study aimed at developing and validating a MEPS-based procedure for the determination in hair of not only AMP and MAMP but also of 3,4-methylenedioxyamphetamine (MDA), 3,4-methylenedioxymethamphetamine (MDMA), 1-(1,3-benzodioxol-5-yl)propan-2-yl (ethyl)amine (MDE) and N-methyl-1-(1,3-benzodioxol-5-yl)-2-aminobutane (MBDB) as well. Hair, 50 mg, was incubated with 1 M sodium hydroxide (NaOH) at 45°C overnight, neutralization with 10 M hydrochloric acid (HCl) and centrifugation followed. The design of experiments approach was used for MEPS optimization, with the final optimized conditions including conditioning (250 µL methanol and deionized water), loading (18 × 100 µL) and elution (7 × 100 µL 2% NH4OH in acetonitrile). The eluted extract was evaporated to dryness and underwent microwave-assisted derivatization with N-methyl-bis(trifluoroacetamide) (MBTFA), and it was afterwards injected onto the gas chromatography-mass spectrometer (GC-MS). The obtained recoveries ranged between 8% and 14% for AMP, 14% and 20% for MAMP, 10% and 15% for MDA, 18% and 28% for MDMA, 25% and 43% for MDE and 34% and 52% for MBDB, and the method was linear from 0.2 to 5.0 ng/mg. Precision and accuracy were in accordance with international method validation guidelines. This novel method involving MEPS coupled to GC-MS offers a swift, eco-friendly and cost-effective alternative to traditional procedures for detecting these AMPs in hair samples.

Development of a high-throughput liquid chromatography-tandem mass spectrometry platform for the determination of intact natriuretic peptides in human plasma.

We present an innovative, reliable, and antibody-free analytical method to determine multiple intact natriuretic peptides in human plasma. These biomolecules are routinely used to confirm the diagnosis and monitor the evolution of heart failure, so that their determination is essential to improve diagnosis and monitor the efficacy of treatment. However, common immunoassay kits suffer from main limitations due to high cross-reactivity with structurally similar species. In our method, we pre-treated the sample by combining salting-out with ammonium sulfate with microextraction by packed sorbent technique. Analyses were then carried out by ultra-high performance liquid chromatography-electrospray ionization-tandem mass spectrometry. The use of 3-nitrobenzyl alcohol as a supercharger reagent enhanced the ESI ionization and improved the signal-to-noise ratio. The analytical protocol showed good linearity over one order of magnitude, recovery in the range of 94-105 %, and good intra- and inter-day reproducibility (RSD<20 %), and the presence of a matrix effect. Limits of detection were in the range of pg/mL for all peptides (0.2-20 pg/mL). Stability study in plasma samples demonstrated that proper protease inhibitors need to be included in blood collection tubes to avoid peptide degradation. Preliminary analyses on plasma samples from heart failure patients allow the quantification of ANP 1-28 as the most abundant species and the detection of ANP 5-28, BNP 1-32, and BNP 5-32. The method could be used to investigate how cross-reactivity issues among structurally similar species impact determinations by ELISA kits.

Green analytical toxicology method for determination of synthetic cathinones in oral fluid samples by microextraction by packed sorbent and liquid chromatography-tandem mass spectrometry.

PURPOSE: We developed and validated a method for quantitative analysis of ten synthetic cathinones in oral fluid (OF) samples, using microextraction by packed sorbent (MEPS) for sample preparation followed by liquid chromatography‒tandem mass spectrometry (LC‒MS/MS). METHOD: OF samples were collected with a Quantisal™ device and 200 µL was extracted using a C18 MEPS cartridge installed on a semi-automated pipette and then analyzed using LC‒M/SMS. RESULTS: Linearity was achieved between 0.1 and 25 ng/mL, with a limit of detection (LOD) of 0.05 ng/mL and a limit of quantification (LOQ) of 0.1 ng/mL. Imprecision (% relative standard deviation) and bias (%) were better than 11.6% and 7.5%, respectively. The method had good specificity and selectivity against 9 different blank OF samples (from different donors) and 68 pharmaceutical and drugs of abuse with concentrations varying between 400 and 10,000 ng/mL. No evidence of carryover was observed. The analytes were stable after three freeze/thaw cycles and when kept in the autosampler (10 °C) for up to 24 h. The method was successfully applied to quantify 41 authentic positive samples. Methylone (mean 0.6 ng/mL, median 0.2 ng/mL), N-ethylpentylone (mean 16.7 ng/mL, median 0.35 ng/mL), eutylone (mean 39.1 ng/mL, median 3.6 ng/mL), mephedrone (mean 0.5 ng/mL, median 0.5 ng/mL), and 4-chloroethcathinone (8.1 ng/mL) were quantified in these samples. CONCLUSION: MEPS was an efficient technique for Green Analytical Toxicology purposes, which required only 650 µL organic solvent and 200 µL sodium hydroxide, and the BIN cartridge had a lifespan of 100 sample extractions.

Automated microextraction by packed sorbent of endocrine disruptors in wastewater using a high-throughput robotic platform followed by liquid chromatography-tandem mass spectrometry.

An automated microextraction by packed sorbent followed by liquid chromatography-tandem mass spectrometry (MEPS-LC-MS/MS) method was developed for the determination of four endocrine disruptors-parabens, benzophenones, and synthetic phenolic antioxidants-in wastewater samples. The method utilizes a lab-made repackable MEPS device and a multi-syringe robotic platform that provides flexibility to test small quantities (2 mg) of multiple extraction phases and enables high-throughput capabilities for efficient method development. The overall performance of the MEPS procedure, including the investigation of influencing variables and the optimization of operational parameters for the robotic platform, was comprehensively studied through univariate and multivariate experiments. Under optimized conditions, the target analytes were effectively extracted from a small sample volume of 1.5 mL, with competitive detectability and analytical confidence. The limits of detection ranged from 0.15 to 0.30 ng L-1, and the intra-day and inter-day relative standard deviations were between 3 and 21%. The method's applicability was successfully demonstrated by determining methylparaben, propylparaben, butylated hydroxyanisole, and oxybenzone in wastewater samples collected from the São Carlos (SP, Brazil) river. Overall, the developed method proved to be a fast, sensitive, reliable, and environmentally friendly analytical tool for water quality monitoring.

Microextraction by packed sorbent of some ß-blocker drugs with chitosan@mof-199 bio-composite in human saliva, plasma, and urine samples.

The current study introduces microextraction by packed sorbent (MEPS) to extract three beta-blocker drugs (propranolol, atenolol, and betaxolol) from biological samples. The separation and detection of the drugs were performed by high performance liquid chromatography followed by UV detection. A green approach was applied for synthesizing chitosan@MOF-199 bio-composite, which was packed into the initial part of a metal spinal (22 gage). The effective parameters on the adsorption and desorption efficiencies, including sample solution pH, eluent flow rate, cycle numbers, type and volume of eluent solvent were evaluated and optimized. Under optimal conditions linear ranges (LRs = 5-600 µg L-1), limits of detection (LODs = 1.5-4.5 µg L-1), and relative standard deviations (RSDs% = 4.7 -5.3% with three replicates and concentration of 100 µg L-1) were obtained. Relative recoveries (RR%) for plasma (77-99%), saliva (81-108%), and urine (80-112%) samples were obtained. In this study, the drug release profile of propranolol in urine was evaluated. The results showed that the highest amount of propranolol is released 4 h after taking the drug. Based on the obtained results, this is an effective, fast, sensitive, reproducible, green, and user-friendly method for beta-blocker drug extraction in biological samples.

Determination of synthetic hallucinogens in oral fluids by microextraction by packed sorbent and liquid chromatography-tandem mass spectrometry.

A fast and simple procedure based on microextraction by packed sorbent (MEPS) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) has been developed for the simultaneous quantification of 28 synthetic hallucinogens in oral fluids, including lysergic acid diethylamide and substances from NBOMe, NBOH, NBF, 2C, and substituted amphetamine categories. Extraction conditions such as type of sorbent, sample pH, number of charge/discharge cycles, and elution volume were studied. Hallucinogenic compounds were extracted from oral fluid samples using C18 MEPS, loading with 100 µL sample (adjusted to pH 7) in 3 cycles, washing with 100 µL deionized water, and eluting with 50 µL methanol in 1 cycle, giving quantitative recoveries and no significant matrix effects. Limits of detection from 0.09 to 1.22 µg L-1; recoveries from 80 to 129% performed in spiked oral fluid samples at 20, 50, and 100 µg L-1; and high precision with relative standard deviations lower than 9% were obtained. The proposed methodology was demonstrated to be appropriate for the simple and sensitive determination of NBOMe derivates and other synthetic hallucinogenic substances in oral fluid samples.

Assessment of benzothiazoles, benzotriazoles and benzenesulfonamides in environmental waters using an optimized combination of microextraction by packed sorbent with programmed temperature vaporization-gas chromatography tandem-mass spectrometry.

This work proposes a new method for the quantification of benzothiazoles (BTs), benzotriazoles (BTRs), and benzenesulfonamides (BSAs) in tap water, river water, and wastewater. The protocol involved the use of microextraction by packed sorbent (MEPS), applied for the first time for the extraction of the target analytes, combined with programmed temperature vaporization-gas chromatography-triple quadrupole mass spectrometry (PTV-GC-QqQ-MS). Considering the synergism between MEPS extraction and PTV injection, the experimental variables affecting their performance were simultaneously optimized by "experimental design", while principal component analysis (PCA) was used to find the overall optimal working conditions. Response surface methodology was used to gain a comprehensive understanding of the effects of working variables on method performance. The developed method achieved very good linearities and satisfactory intra- and inter-day accuracies and precisions. The protocol permitted the detection of the target molecules with limit of detection (LODs) values between 0.005 and 0.85 µg/L. The green character of the procedure was evaluated using three metrics: "Analytical Eco-Scale", "Green Analytical Procedure Index" (GAPI), and "Analytical Greenness metric for sample preparation (AGREEprep). The satisfactory results obtained with real water samples demonstrate the applicability of the method for monitoring campaigns and exposome studies.

Novel eco-friendly methodology to determine polycyclic aromatic hydrocarbons in polyurethane foam for air monitoring: Application to spatial and temporal distribution survey.

This study aimed at developing a new method for the extraction of polycyclic aromatic hydrocarbons (PAHs) in polyurethane foam (PUF). In the field of PAH monitoring, passive samplers using PUF disks are widely used. However, current extraction methods are time and solvent consuming. This new method employs 3 times a sixteenth of the PUF disk, with method detection limits (MDL) values below 5 and 13 ng/sampler for 3- and 4-rings PAHs, respectively. The use of only parts of the disk allows extraction by ultrasounds using exclusively 120 mL of ethanol, making it environmentally friendly. Ethanolic extracts are then purified and concentrated using microextraction by packed sorbent (MEPS) before GC-MS analyses. This method was applied for an environmental survey in a French urban area with an oceanic climate. Variations in PAH concentrations were observed depending on the site studied (urban, traffic, periurban and rural), as well as temporal variations.

Determination of Hydroxy Polycyclic Aromatic Hydrocarbons in Human Urine Using Automated Microextraction by Packed Sorbent and Gas Chromatography-Mass Spectrometry.

A fast methodology for the determination of monohydroxy polycyclic aromatic hydrocarbons in human urine using a fully automated microextraction by packed sorbent coupled to a gas chromatograph-mass spectrometer is reported. Sample preparation requires simple hydrolysis, centrifugation, filtration, and dilution. The method does not require a derivatization step prior to analysis with gas chromatography and allows the measurement of up to three samples per hour after hydrolysis. Quantitation is carried out by a one-point standard addition allowing the determination of 6 analytes with good limits of detection (10.1-39.6 ng L-1 in water and 0.5-19.4 µg L-1 in urine), accuracy (88-110%) and precision (2.1-23.4% in water and 5.1-19.0% in urine) values. This method has been successfully applied to the analysis of six urine samples (three from smoker and three from non-smoker subjects), finding significant differences between both types of samples. Results were similar to those found in the literature for similar samples, which proves the applicability of the methodology.

The Determination of Cannabinoids in Urine Samples Using Microextraction by Packed Sorbent and Gas Chromatography-Mass Spectrometry.

Cannabis is the most consumed illicit drug worldwide, and its legal status is a source of concern. This study proposes a rapid procedure for the simultaneous quantification of Δ9-tetrahydrocannabinol (THC), 11-hydroxy-Δ9-tetrahydrocannabinol (11-OH-THC), 11-nor-9-carboxy-Δ9-tetrahydrocannabinol (THC-COOH), cannabidiol (CBD), and cannabinol (CBN) in urine samples. Microextraction by packed sorbent (MEPS) was used to pre-concentrate the analytes, which were detected by gas chromatography-mass spectrometry. The procedure was previously optimized, and the final conditions were: conditioning with 50 µL methanol and 50 µL of water, sample load with two draw-eject cycles, and washing with 310 µL of 0.1% formic acid in water with 5% isopropanol; the elution was made with 35 µL of 0.1% ammonium hydroxide in methanol. This fast extraction procedure allowed quantification in the ranges of 1-400 ng/mL for THC and CBD, 5-400 ng/mL for CBN and 11-OH-THC, and 10-400 ng/mL for THC-COOH with coefficients of determination higher than 0.99. The limits of quantification and detection were between 1 and 10 ng/mL using 0.25 mL of sample. The extraction efficiencies varied between 26 and 85%. This analytical method is the first allowing the for determination of cannabinoids in urine samples using MEPS, a fast, simple, and low-cost alternative to conventional techniques.

Detection and quantification of prostaglandin E2 in saliva by liquid chromatography-tandem mass spectrometry using microextraction by packed sorbent.

The detection of eicosanoids in saliva samples can assist pharmacokinetic/pharmacodynamic studies due to the facility of obtaining samples, minimal discomfort and high adherence of volunteers to the study. The present study enabled determine prostaglandin E2 concentrations in saliva samples, using a microextraction by packed sorbent methodology and subsequent detection in liquid chromatography-tandem mass spectrometry. Twelve volunteers underwent scaling and coronary-radicular polishing of the upper molars and sequential saliva collections: 0.25-96 h after ingestion of a 600 mg ibuprofen tablet, to quantify prostaglandin E2 concentrations. There was an increase in the level of prostaglandin E2 with a significant difference after the dental procedure (0.25 h) compared to 11, 24, 48 and 72 h (*p < 0.05). After taking the drug, these levels begin to decrease up to 5 h, returning to normal in the subsequent hours. The method was developed and validated with linearity between 2.4 and 1250 ng/mL and r2 above 0.9932. The limit of quantitation was about 2.4 ng/mL. The coefficients of variation and the relative standard errors of the accuracy and precision analyzes were < 15%. The proposed extraction and analysis methodology proved to be efficient, fast and promising for pharmacokinetic/pharmacodynamic assays after using anti-inflammatory drugs.

Analysis of opiates in urine using microextraction by packed sorbent and gas Chromatography- Tandem mass spectrometry.

Opiates recreational consumption has always been a concern in society, public health, and in clinical toxicology analysis. The aim of this study was to develop and fully validate an analytical method, which was simple and rapid for the determination of tramadol, codeine, morphine, 6- acetylcodeine, 6-monoacetylmorphine and fentanyl using gas chromatography coupled to tandem mass spectrometry. The procedure includes the use of microextraction by packed sorbent for sample clean-up. A mixed mode sorbent was used, allowing the minimal use of solvents. The method was validated in urine samples, with the ability to detect and quantify all analytes with satisfactory linearity (in the range of 1 - 1000 ng/mL for all analytes, except for fentanyl (10-1000 ng/mL)). Extraction efficiency varied from 17 to 107%, which did not impair sensitivity, taking into account the low LLOQs obtained (1 ng/ mL for all analytes; and 10 ng/mL for fentanyl). The developed procedure proved to be fast, selective, and accurate for use in routine analysis, with a low volume of sample (250 µL).

Application of Fe3O4@TbBd nanobeads in microextraction by packed sorbent (MEPS) for determination of BTEXs biomarkers by HPLC-UV in urine samples.

A relatively new adsorbent based on covalent organic frameworks (COFs) was employed for the first time to extract and determine Trans, trans-muconic acid (tt-MA), Mandelic acid (MA), Hippuric acid (HA), and 3-Methylhippuric acid (m-MHA) in urine. For this purpose, microextraction was performed using the packed sorbent (MEPS) method. Following the extraction process, the prepared samples were specified via the high-performance liquid chromatography-ultraviolet detector system. The precipitation polymerization was applied to synthesize the Fe3O4@TbBd nanobeads, and the morphological and dimensional structures of the products were specified with FE-SEM images. Some key variables affecting the extraction efficiency (i.e., sample volume, elution volume, condition and washing solvents, type and volume of elution solvent, extraction cycles, temperature, and pH of the sample solution) were investigated. In ideal conditions, the limit of detection (LOD) was obtained from 0.02 µg/ml for tt-MA to 0.5 µg/ml for MA. Calibration curves (at five-point) were plotted in the range 0.05-5 µg/ml for tt-MA to 1-300 µg/ml for MA (R2 > 0.98). Moreover, intra- and inter-day precision values were 3.1-5.5 and 4.6-9.8%, respectively. The developed method was successfully employed to determine four analytes in three concentrations (low, medium, and high QCs). The results showed a satisfactory recovery (70-87%). COF-MEPS technique is a rapid, easy, user-friendly, and environment-friendly method for separating the minimum values of all BTEXs chief biomarkers from urine samples without using complicated processes and only with one adsorbent. Also, it can be a good alternative for biomonitoring the workers exposed to BTEX compounds in occupational and environmental access.

The Potential of Microextraction Techniques for the Analysis of Bioactive Compounds in Food.

For a long time, the importance of sample preparation and extraction in the analytical performance of the most diverse methodologies have been neglected. Cumbersome techniques, involving high sample and solvent volumes have been gradually miniaturized from solid-phase and liquid-liquid extractions formats and microextractions approaches are becoming the standard in different fields of research. In this context, this review is devoted to the analysis of bioactive compounds in foods using different microextraction approaches reported in the literature since 2015. But microextraction also represents an opportunity to mitigate the environmental impact of organic solvents usage, as well as lab equipment. For this reason, in the recent literature, phenolics and alkaloids extraction from fruits, medicinal herbs, juices, and coffee using different miniaturized formats of solid-phase extraction and liquid-liquid microextraction are the most popular applications. However, more ambitious analytical limits are continuously being reported and emergent sorbents based on carbon nanotubes and magnetic nanoparticles will certainly contribute to this trend. Additionally, ionic liquids and deep eutectic solvents constitute already the most recent forefront of innovation, substituting organic solvents and further improving the current microextraction approaches.

Microextraction by packed sorbent of selected pesticides in coffee samples employing ionic liquids supported on graphene nanosheets as extraction phase.

This paper describes the synthesis, characterization, and use of ionic liquids supported on silica, functionalized with graphene oxide through covalent bonding (ILz/Si@GO), as sorbents for microextraction by packed sorbent (MEPS). Seven selected pesticides (diazinon, heptachlor, aldrin, endrin, dieldrin, endosulfan, and methoxychlor), used for the prevention of pests in coffee crops, and endosulfan sulfate-an endosulfan metabolite-were selected for this study as model compounds for evaluating the sorbent performance of the synthesized materials in the MEPS device. The cycles of each of the stages were previously optimized through univariate experiments to carry out the extraction. The ILz/Si@GO phase was compared to other sorbents used in MEPS (GO, DVB-MMA, C4/SiO2, C8/SiO2, ILz/SiO2, and bare silica) and also with graphene functionalized through other methodologies, where ILz/Si@GO showed the best results. The material was characterized using a range of techniques. The selectivity of the sorbent material and its adsorption capacity were evaluated by gas chromatography coupled with tandem mass spectrometry. The precision and accuracy of the method showed a relative standard deviation lower than 10% and recoveries from 35 to 97%. Finally, the proposed method was employed for the determination of pesticide residues in coffee samples.

Determination of Benzophenones in Water and Cosmetics Samples: A Comparison of Solid-Phase Extraction and Microextraction by Packed Sorbent Methods.

Benzophenones (BPs) are extensively used in a wide variety of cosmetic products and other materials (e.g., textiles or plastics) to avoid damaging effects of UV radiation. In the present work, we compared two extraction methods for the determination of BPs, namely, 2,4-dihydroxybenzophenone (BP-1), 2-hydroxy-4-methoxybenzophenone (BP-3) and 2,2-dihydroxy-4-methoxybenzophenone (BP-8), in water and cosmetics samples. The following extraction methods were used for the research: solid-phase extraction (SPE) and microextraction by packed sorbent (MEPS), whereas analysis was performed by gas chromatography with mass spectrometric detection. A comparison between the methods indicates that the MEPS technique(s) can be reliably used for analysis of BPs (sunscreen residue) in water samples and cosmetic samples with satisfactory results. This microextraction technique is cheap, easy, quick to implement, and consumes small amounts of solvents. On the other hand, the main advantage of the SPE method are low detection limits for the determination of BPs in water samples, i.e., from 0.034 to 0.067 µg L-1, while, for the MEPS method, LODs were at the level of 1.8-3.2 µg L-1. For both methods, the recoveries of BPs were 96-107% and 44-70% for water and cosmetics samples, respectively. The presented methods are suitable for use in cosmetics quality control and environmental pollution assessment.

[Research progress of microextraction by packed sorbent and its application in microvolume sample extraction].

Microextraction is a rapidly developing sample preparation technology in the field of analytical chemistry, which is seeing widespread application. Accurate sample preparation can not only save time but also improve the efficiency of analysis, determination, and data quality. At present, sample pretreatment methods must be rapid, allow for miniaturization, automation, and convenient online connection with analytical instruments. To meet the requirements of green analytical methods and improve the extraction efficiency, microextraction techniques have been introduced as suitable replacements to conventional sample preparation and extraction methods. Microextraction using a packed sorbent (MEPS) is a new type of sample preparation technology. The MEPS equipment was prepared using microsyringe with a volume of 50-500 µL, including MEPS syringes and MEPS adsorption beds (barrel insert and needle, BIN), which is essentially similar to a miniaturized solid phase extraction device. The BIN contains the adsorbent and is built into the syringe needle. A typical MEPS extraction procedure involves repeatedly pumping the sample solution in two directions (up and down) through the adsorbent multiple times in the MEPS syringe. The specific operation course of MEPS includes conditioning, loading, washing, elution, and introduction into the analysis instrument. The conditioning process is adopted to infiltrate the dry sorbent and remove bubbles between the filler particles. The adsorption process is accomplished by pulling the liquid plunger of the syringe so that the sample flows through the adsorbent in both directions multiple times. The washing process involves rinsing the sorbent to remove unwanted components after the analyte is retained. The elution process involves the use of an eluent to ensure that the sample flows through the adsorbent in both directions multiple times, so that elution can be realized by the pumping-pushing action. The target analyte is eluted with the eluent, which can be directly used for chromatographic analysis. However, when processing complex biological matrix samples by MEPS, pretreatment steps such as dilution of the sample and removal of proteins are commonly required. At present, the operation modes of the MEPS equipment are classified into three types: manual, semi-automated, and fully automated. This increase in the degree of automation is highly conducive to processing extremely low or extremely high sample volumes. Critical factors affecting the MEPS performance have been investigated in this study. The conditions for MEPS optimization are the operating process parameters, including sample flow rate, sample volume, number of sample extraction cycles, type and volume of the adsorbent, and elution solvents. It is also necessary to consider the effect of the sample matrix on the performance of MEPS. The MEPS sorbent should be cleaned by a solvent to eliminate carryover and reuse. The sorbent is a core aspect of MEPS. Several types of commercial and non-commercial sorbents have been used in MEPS. Commercial sorbents include silica-based sorbents such as unmodified silica (SIL), C2, C8, and C18. Unmodified silicon-based silica is a normal phase adsorption material, which is highly polar and can be used to retain polar analytes. C18, C8, and C2 materials are suitable for reversed-phase adsorption, while SCX, SAX, APS, and M1 (C8+SCX) adsorbents are suitable for the mixed-mode and ion-exchange modes. Noncommercial sorbents include molecularly imprinted materials, restricted-access molecularly imprinted materials, graphitized carbon, conductive polymer materials, modified silicon materials, and covalent-organic framework materials. The performance of MEPS has recently been illustrated by online with LC-MS and GC-MS assays for the analysis of biological matrices, environmental samples, and food samples. Pretreatment in MEPS protocols includes dilution, protein precipitation, and centrifugation in biological fluid matrices. Because of the small sample size, fast operation, etc., MEPS is expected to be more widely used in the analysis of bio-matrix samples. MEPS devices could also play an important role in field pretreatment and analysis.

Metabolic profiling of aromatic compounds in cerebrospinal fluid of neurosurgical patients using microextraction by packed sorbent and liquid-liquid extraction with gas chromatography-mass spectrometry analysis.

A new approach to the quantitative analysis of aromatic metabolites in cerebrospinal fluid samples of neurosurgical patients based on microextraction by packed sorbent coupled with derivatization and GC-MS was developed. Analytical characteristics such as recoveries (40-90%), limit of detection (0.1-0.3 µm) and limit of quantitation (0.4-0.7 µm) values, accuracy (<±20%), precision (<20%) and linear correlations (R2 ≥ 0.99) over a 0.4-10 µm range of concentrations demonstrated that microextraction by packed sorbent provides results for the quantitative analysis of target compounds comparable with those for liquid-liquid extraction. Similar results were achieved using 40 µl of sample for microextraction by packed sorbent instead of 200 µl for liquid-liquid extraction. Benzoic, 3-phenylpropionic, 3-phenyllactic, 4-hydroxybenzoic, 2-(4-hydroxyphenyl)acetic, homovanillic and 3-(4-hydroxyphenyl)lactic acids were found in cerebrospinal fluid samples (n = 138) of neurosurgical patients in lower concentrations than in serum samples (n = 110) of critically ill patients. Analysis of the cerebrospinal fluid and serum samples taken at the same time from neurosurgical patients (n = 5) revealed similar results for patients without infection and multidirectional results for patients with central nervous system infection. Our preliminary results demonstrate the necessity of further evaluating the aromatic compound profile in cerebrospinal fluid for its subsequent verification for potential diagnostic markers.

Mesoporous molecularly imprinted polymer core@shell hybrid silica nanoparticles as adsorbent in microextraction by packed sorbent for multiresidue determination of pesticides in apple juice.

In this work, we report the synthesis of a mesoporous molecularly imprinted polymer on the surface of silica nanoparticles (core@mMIP) to be applied as adsorbent in microextraction by packed sorbent (MEPS) for selective determination of pesticides in apple juice. The core@mMIP was properly characterized, showing good adhesion of the polymer to the silica core. The best extraction conditions were: 200 µL of ultrapure water as washing solvent, 150 µL of acetonitrile as eluent, 100 µL of sample at pH 2.5, five draw-eject cycles and 8 mg of adsorbent. Thereby, recoveries of 96.12 ± 1.05%, 76.88 ± 6.18% and 76.18 ± 5.57% were obtained for pyriproxyfen (PPX), deltamethrin (DTM) and etofenprox (ETF), respectively. After validation, the method presented linearity in the range of 0.02-10 µg mL-1 (r > 0.99), limit of detection of 0.005 µg mL-1, satisfactory selectivity, and proper precision and accuracy. The method was successfully applied real samples of processed and fresh apple juice.