Functional materials and chemicals in electromembrane extraction

The role of nanomaterials in tailoring electromembrane extraction performance: A review

Electromembrane extraction (EME) is a membrane-based miniaturized microextraction technique used to extract ionized analytes from complex mixtures. EME extracts can be analyzed using all major analytical instrumental techniques. The major advantages of EME include short extraction time, low consumption of organic solvents and chemicals, high extraction capability, high selectivity, and efficient sample cleanup. Numerous modifications to EME, such as the use of microfluidic devices, green solvents, biobased renewable membranes, and hyphenation with other separation techniques, have increased the selectivity and sensitivity of EME. Furthermore, nanomaterials have been used to improve the efficiency, selectivity, and stability of EME systems. Various nanomaterials have been proposed for the modification of EME-based separation systems. The larger surface area, high porosity, and various interactions with the target analytes are the most important properties of nanomaterials and nanocomposites in improving the figures of merit of EME. Nanomaterials have mainly been used to modify the chemical composition of the liquid membrane in EME, but modifications of the polymeric support membrane and the electrodes have also been reported. Therefore, this review highlights the transformative role of nanomaterials in EME, focusing on their application in enhancing extraction efficiency, selectivity, and stability. Key advancements include modifying supported liquid membranes (SLMs), membrane decoration, and optimizing electrode performance. The review also critically examines challenges, such as pore blockage and electrolysis-induced instability, offering insights into future directions for nanomaterial-enhanced EME. Despite of the numerous benefits of nanomaterials, their environmental toxicity cannot be overlooked and should be carefully examined for each new case. A bio-based and biopolymer-based nanomaterials in future EME studies can significantly address these issues while remaining aligned with green chemistry principles. Artificial intelligence-based models should be applied to predict effective nanomaterials in EME, thus significantly reduce chemical costs and consumption while also increasing the greenness level of developed EME approaches. Finally, long-term stability of new developed solutions should be an obligatory part of each new research in this field.

Natural deep eutectic solvent-based hollow polymer inclusion membrane doped with TiO2 nanoparticles: A new design of polymer inclusion membrane for on-chip electromembrane extraction of fluoroquinolones from food samples prior to liquid chromatography tandem mass analysis

A new design of polymer inclusion membrane has been proposed with the aim of addressing issues with using common forms of liquid membranes. To do so, a natural deep eutectic solvent (NADES) was employed as an extractant in the structure of the hollow polymer inclusion membrane (HPIM). Besides polyvinyl chloride (PVC) as a base polymer, titanium dioxide nanoparticles (TiO2) as well as polyethylene glycol polymer (PEG) were incorporated into the HPIM structure to achieve a nanocomposite form with a desirable hydrophilicity. The optimal HPIM was composed of 12.5 v/w% of thymol-coumarin NADES, 3.0 w/w% of TiO2 and 40.0 v/w% of PEG based on PVC content. Aiming to compare the applicability, HPIMs with other types of extractants, such as bis(2-ethylhexyl) phthalate (DEHP), and the mixture of DEHP-NADES were also fabricated. To confirm the successful fabrication of the HPIM, containing the aforementioned extractant doped with TiO2 nanoparticles various characterization techniques were employed. The resultant HPIM was employed as a liquid membrane in an on-chip electromembrane extraction (EME) of fluoroquinolones (FQs) from various samples, followed by LC-MS/MS analysis. The parameters influencing extraction performance were analyzed, and the proposed method was validated under ideal conditions. All the samples provided excellent performance concerning limits of detection (0.01-0.08 ng mL-1), and quantification (0.03-0.25 ng mL-1) together with an excellent linearity (R2 ≥ 0.9978). The method indicates the desirable RSDs% in the range of 3.2-7.0 % (intra-day, n = 3 × 3) and 3.8-6.1 % (inter-day, n = 3 × 3) for three spiked levels. The satisfactory relative recoveries fell within the 92.0-115.0 % range.

Successive electromembrane extraction: A new insight in simultaneous extraction of polar and non-polar metabolic molecules from biological samples

BACKGROUND

Simultaneous determination of different natures of analytes is of great significance for saving sample volumes and simplifying analytical procedures. However, sample preparation for the simultaneous extraction of polar and non-polar analytes represents a challenge in sample preparation. Inspired by the successive liquid-phase microextraction (sLPME) method for acidic and basic analytes that we previously developed, we first proposed an efficient successive electromembrane extraction (sEME) system by adjusting the acidity of the donor solution and using binary organic solvents for extraction of polar and non-polar targets from biological samples in this work.

RESULTS

We performed a detailed optimization of the sEME system. Here, carnitine (C0) and acylcarnitines were selected as model analytes since the demand increased especially in metabolomics studies. The combination of 2-nonanone and 2-nitrophenylpentyl ether (NPPE) was selected as supported liquid membranes (SLMs), and trichloroacetic acid (TCA) 100 % (v/v) was added to donor solution to adjust the acidity of the donor solution after the first sEME process (sEME-1). The recoveries of the targets in blood and urine were 47%-119% and 54%-118%, respectively. Moreover, the sEME systems were evaluated by liquid chromatography tandem mass spectrometry (LC-MS/MS) from biological samples. The limit of detection (LOD) and limit of quantitation (LOQ) of analytes were 0.03-1.33 ng mL-1 and 0.09-4.42 ng mL-1, respectively.

SIGNIFICANCE

sEME enabled the extraction of polar and non-polar analytes from the same sample under optimal extraction conditions for all target analytes, which provided ideas for efficient sEME of exogenous and endogenous analytes from biological samples for forensic, clinical, and epidemiological studies.

New robust and efficient liquid membranes for conductive vial electromembrane extraction of acids with low to moderate hydrophilicity in human plasma

The current paper reports two new, robust, and efficient conditions for electromembrane extraction of acidic substances from human plasma. Two systems were developed based on eutectic solvents: A1 ("A" for acid) comprised dodecyl methyl sulfoxide and thymol in 1:2 ratio (w/w) as liquid membrane, while A2 used [6-methylcoumarin:thymol (1:2)]:2-nitrophenyl octyl ether in 2:1 ratio (w/w). The performance of A1 and A2 was characterized by extraction of 31 acidic model analytes (pharmaceutical drugs and nutrients) spiked into 100 µL human plasma diluted 1:1 (v/v) with phosphate buffer pH 7.4. The acceptor solution was 50 mM NH4HCO3 buffer pH 10.0, and extraction was performed at an agitation rate of 750 RPM. Voltage and extraction time were 30 V for 30 min and 10 V for 20 min for A1 and A2, respectively. Under optimal conditions, A1 extracted analytes with 1.8 ≤ log P ≤ 6.0 with an average recovery (R) of 85.1%, while A2 extracted in a range of 0.5 ≤ log P ≤ 6.0 with an average recovery of 79.9%. Meanwhile, extraction current was low at 9 and 26 µA, respectively, which is indicative of good system robustness. Using UHPLC-MS/MS analysis of the acceptor solution, repeatability of the A1 and A2 methods was determined to be 2.8-7.7% and 3.3-9.4% for R > 40%, matrix effects were 82-117% and 84-112%, respectively, and linear calibration curves were obtained. The performance and compatibility with human plasma represent a major improvement over previous state-of-the-art liquid membranes for acidic analytes, namely 1-octanol.

Dual microelectromembrane extraction as a tunable platform for the determination of antioxidant compounds with varied hydrophobicity in oral bioaccessibility assays of food commodities: a proof of concept

An automatic millifluidic dual microelectromembrane extraction (D-µEME) method as a front-end to HPLC-UV-Vis is herein proposed for the first time to facilitate the matrix clean-up of relatively polar polyphenolic acidic (PPA) antioxidants with a relatively broad range of lipophilicity (logP from -0.27 to 2.14) from simulated gastric extracts of oral bioaccessibility tests. The flow setup is amenable to handle microliter volumes of two distinct organic phases along with donor and acceptor phases unsupervised, conduct in-tube D-µEME in parallel without supporting membranes, and mix the two acceptor phases automatically prior to online HPLC-UV-Vis. The target antioxidants involve gallic acid, chlorogenic acid, 4-hydroxybenzoic acid, caffeic acid, and trans-cinnamic acid. Various solvents are explored to investigate their compatibility for simultaneous D-µEME, including 1-pentanol, 1-hexanol, 1-heptanol, 1-octanol, and 1-nonanol, as well as deep eutectic solvents, e.g., thymol/6-methyl coumarin, and ionic liquids as additives to alcohols. Notably, 1-pentanol and 1-octanol exhibit the best performances in extracting the most polar (gallic acid and chlorogenic acid) and the least polar analytes (trans-cinnamic acid), respectively, notwithstanding both solvents are amenable to retrieve analytes with medium hydrophobicity (4-hydroxybenzoic acid and caffeic acid). The effects of the voltage, the extraction time, and the sample ionic strength on the extraction recoveries are also investigated in detail. Under the selected D-µEME conditions, the overall linear ranges span from 1.25 to 80 mg/L, with limits of detection ranging from 0.2 to 3.3 mg/L. The flow-based D-µEME is resorted to oral bioaccessibility assays in the gastric phase of the target compounds from eggplant, blueberry, and coffee bean extracts, with relative extraction recoveries ranging from 71.5 to 133.5%.

Electroextraction of Large Volume Samples Using Paper Points Coupled With Hollow Fiber Membranes: Study of Parameters and Strategies to Enhance Analytical Performance

Electroextraction (EE) encompasses a range of sample preparation methods whose effectiveness, selectivity, and efficiency are significantly influenced by the physical-chemical characteristics of analytes, samples, and instrumental conditions. This article explores, for the first time, various strategies aimed at enhancing the extraction efficiency of a recent approach of EE utilizing a paper point (PP) combined with a hollow fiber (HF) (abbreviated as PP-HF-EE) to extract various cationic and anionic model compounds from water samples. The study also explores, experimentally, the impact of agitation, organic filter composition, PP diameter, and PP brand on extraction performance, and proves that all these factors are quite important, especially when digital image analysis is utilized for determination. Furthermore, this work demonstrates the ease and feasibility of simultaneously extracting cations and anions using PP-HF-EE and proposes a straightforward method to enhance analyte concentration on the vertex of the PP through a base-to-vertex focusing. Lastly, it is demonstrated, using capillary electrophoresis coupled to a UV-Vis detector, that for PP-HF-EE, the extraction efficiency and pre-concentration factor are less dependent on other parameters when multiple PPs per sample are utilized, with signal enhancement values of up to 111 and 339 for nortriptyline and haloperidol, respectively. All the findings and strategies presented herein constitute significant contributions that can facilitate future research in method development, particularly in the utilization of PP-HF-EE and similar EE approaches.

Confined Gel-Electromembrane Extraction of Oligonucleotides

Gel-electromembrane extraction (G-EME) is an increasingly popular green variant of electromembrane extraction (EME). However, the electroendosmosis (EEO) flow associated with G-EME greatly limits the development of this technology. To address this challenge, the current study proposed the concept of confined G-EME (CG-EME), and a three-dimensional-printed modular device was elaborately designed to realize this concept. The device blocked the EEO flow by limiting the volume of the sample compartment. Moreover, the mesh structure at the bottom of the extraction module helps to prepare thin and stable gel films, which enhance the electromigration driving force and shorten the migration path. In addition, polar oligonucleotides, a nucleic acid analyte, were extracted for the first time to prove the concept of CG-EME. After optimization, 62% of the oligonucleotides were extracted at 50 V voltage for 15 min using a 3 mm thick agarose (3%) gel film. Finally, the application capability of CG-EME was further demonstrated by recovering DNA primers and isolating disease biomarkers (miRNA-181b) from real samples. In combination with CG-EME and quantitative polymerase chain reaction (qPCR) analysis, the upregulation of miRNA-181b expression in the peripheral blood of patients with schizophrenia was observed. In conclusion, this study proposes CG-EME to diminish EEO and push EME into the clinical field to isolate nucleic acid biomarkers, which will greatly expand the application scenarios of this emerging technology.

Chemical nature evolution of solid supports used in electromembrane extraction procedures: A comparative analysis based on metric tools

BACKGROUND

In recent decades, green chemistry has been focusing on the adaptation of different chemical methods towards environmental friendliness. Sample preparation procedures, which constitute a fundamental step in analytical methodology, have also been modified and implemented in this direction. In particular, electromembrane extraction (EME) procedures, which have traditionally used plastic supports, have been optimized towards greener approaches through the emergence of alternative materials. In this regard, biopolymer-based membranes (such as agarose or chitosan) have become versatile and very promising substitutes to perform these processes.

RESULTS

Different green metric tools (Analytical Eco-Scale, ComplexGAPI and AGREEprep have been applied to study the evolution of solid supports used in EME from nanostructured tissues and polymer inclusion membranes to agar films and chitosan flat membranes. The main goal is to evaluate the usage of these new biomaterials in the analytical procedure to quantify their environmental impact in the frame of Green Analytical Chemistry (GAC). In addition, both RGB model and BAGI metrics have been employed to study the sustainability of the whole procedure, including not only greenness, but also analytical performance and feasibility aspects. Results obtained after the performance of the mentioned metrics have demonstrated that the most efficient and environmentally friendly analytical methods are based on the use of chitosan supports. This improvement is mainly due to the chemical nature of this biopolymer as well as to the removal of organic solvents.

SIGNIFICANCE

This work highlights the advantages of biodegradable materials employment in EME procedures to achieve green analytical methodologies. These materials also contribute to raise the figure of merits regarding to the quantification parameters in a wide range of applications compared to classical supports employed in EME, thus enhancing sustainability of procedures.

Determination of chromium species in water using diphenylcarbazide with a sequential spectrophotometric discrete robotic analyser

There is an increasing need for fast and reliable analytical methods for the determination of chemical forms of elements in environmental samples. The interest in chromium is driven by the fact that its toxicity depends on its oxidation state. Although chromium (III) is essential for mammals to maintain their metabolism of proteins, fats, and carbohydrates, chromium (VI) is toxic to humans. For chromium speciation, several costly analytical methods coupling separation methods with atomic absorption and emission spectroscopy have been developed. This article presents the online robotic discrete analyser procedure with the 1,5 diphenylcarbazide (DPC) method for the speciation of Cr (III) and Cr (VI). Cr (III) was determined by difference since it does not interfere with the reaction of Cr (VI)-DPC. Chromium (VI) and total chromium were characterised sequentially (after online oxidation of Cr (III) by Cerium (Ce (IV)). The calibration graphs were linear under experimental conditions up to 1 mg/L Cr (VI) and 2 mg/L total Cr with correlation coefficient R2, 0.9997 and 0.9999 respectively. At a signal-to-noise ratio of three, the detection limits were 0.004 mg/L Cr (VI) and 0.015 mg/L total Cr. Good agreement between the real values of certified reference materials and the chromium species content was obtained in this study. The method was precise with a percentage relative standard deviation of less than 2 for hexavalent chromium and total chromium. The t-stat demonstrates that there was no significant difference between the developed robotic discrete analyser method and the ICP-MS method. Except for effluent water, which had recoveries between 65 and 75 % in the assessment of the devised method's selectivity, the overall percentage of recoveries fell between 90 and 110 %, which was generally satisfactory. This method proved to be appropriate for its intended use.

Enhancing the Concentration Capability of Nonsupported Electrically Driven Liquid-Phase Microextraction through Programmable Flow Using an All-In-One 3D-Printed Optosensor: A Proof of Concept

A versatile millifluidic 3D-printed inverted Y-shaped unit (3D-YSU) was prototyped to ameliorate the concentration capability of nonsupported microelectromembrane extraction (μ-EME), exploiting optosensing detection for real-time monitoring of the enriched acceptor phase (AP). Continuous forward-flow and stop-and-go flow modes of the donor phase (DP) were implemented via an automatic programmable-flow system to disrupt the electrical double layer generated at the DP/organic phase (OP) interface while replenishing the potentially depleted layers of analyte in DP. To further improve the enrichment factor (EF), the organic holding section of the OP/AP channel was bifurcated to increase the interfacial contact area between the DP and the OP. Exploiting the synergistic assets of (i) the continuous forward-flow of DP (1050 μL), (ii) the unique 3D-printed cone-shaped pentagon cross-sectional geometry of the OP/AP channel, (iii) the bifurcation of the OP that creates an inverted Y-shape configuration, and (iv) the in situ optosensing of the AP, a ca. 24 EF was obtained for a 20 min extraction using methylene blue (MB) as a model analyte. The 3D-YSU was leveraged for the unsupervised μ-EME and the determination of MB in textile dye and urban wastewater samples, with relative recoveries ≥88%. This is the first work toward analyte preconcentration in μ-EME with in situ optosensing of the resulting extracts using 3D-printed millifluidic platforms.

Electroextraction of methylene blue from aqueous environmental samples using paper points coupled with hollow fiber membranes

This article introduces a novel approach by coupling paper points with hollow fiber membrane for electroextraction (PP-HF-EE). The method was innovatively applied to extract methylene blue (MB) from large water volumes (up to 580 mL). A comprehensive study of six key parameters - organic filter, acceptor and donor phase composition, extraction time, applied voltage, and sample volume - was conducted using conventional flatbed scanning and digital image analysis. Our results revealed that extraction performance was primarily influenced by time, with low voltages (50 V) and low-conductivity organic filters (1-decanol) yielding comparable results to higher settings (300 V or 1-pentanol). Under optimized conditions (50 V, 60 min, 1-decanol as the organic filter), analytical performance parameters were assessed, demonstrating acceptable precision (RSD <18% for intra- and inter-day measurements) within a linear range of 5-100 μg L-1 (r = 0.98). PP-HF-EE demonstrated reliability through stable and reproducible electric current measurements during all extraction studies. Utilizing an extremely cost-effective detection system, PP-HF-EE achieved detection limits in the low ppb range, highlighting its potential as a promising variation of electromembrane extraction for environmental sample analysis.

Introduction of an electrospun nanofibrous membrane incorporated by metal-organic framework-199 (MOF-199) with Lewis acid property for efficient extraction of sulfonamides in on-chip electromembrane extraction

In this study, a new supporting polymeric membrane having Lewis acid nature was introduced for immobilizing organic solvent in on-chip electromembrane extraction (on-chip EME). For this aim, a polymeric nanofibrous membrane incorporated by a copper based metal-organic framework (MOF-199), with coordinatively unsaturated metal sites and Lewis acid property, was prepared by electrospinning a mixture of polycaprolactone (PCL) and MOF-199. Based on the field emission scanning electron microscopy images, the obtained polymeric membrane consisted of intertwined nanofibers having empty space between the fibers which could provide a suitable place for immobilizing the organic solvent. To demonstrate remarkable extractability of the proposed membrane (PCL/MOF-199 nanofibers) via executing Lewis acid-base interactions, three sulfonamide drugs was selected as anionic polar analytes with Lewis base feature. The parameters affecting the extraction efficiency of the method were optimized through the experimental design method using the orthogonal and rotatable central composite design (CCD). Under optimum conditions, the extraction recoveries ranging from 35.5 to 71.2 %, the relative standard deviations (RSD%) less than 6.45 %, and the detection limits in the range of 0.2-0.5 μg L-1 were achieved. The comparison of the extraction efficiency of the on-chip EME method using the electrospun PCL/MOF-199 nanofibers and PCL nanofibers membranes indicated that the proposed membrane was more efficient for extraction of sulfonamides because of the significant Lewis acid-base interactions of sulfonamides with copper uncoordinated open sites in MOF-199. Finally, the performance of the proposed method for extraction and determination of sulfonamides in three real samples was assayed.

3D-printed stereolithographic fluidic devices for automatic nonsupported microelectromembrane extraction and clean-up of wastewater samples

BACKGROUND

There is a quest of novel functional and reliable platforms for enhancing the efficiency of microextraction approaches in troublesome matrices, such as industrial wastewaters. 3D printing has been proven superb in the analytical field to act as the springboard of microscale extraction approaches.

RESULTS

In this work, low-force stereolithography (SL) was exploited for 3D printing and prototyping bespoke fluidic devices for accommodating nonsupported microelectromembrane extraction (μEME). The analytical performance of 3D-printed μEME devices with distinct cross-sections, including square, circle, and obround, and various channel dimensions was explored against that of commonly used circular polytetrafluoroethylene (PTFE) tubing in flow injection systems. A computer-controlled millifluidic system was harnessed for the (i) automatic liquid-handling of minute volumes of donor, acceptor, and organic phases at the low μL level that spanned from 3 to 44 μL in this work, (ii) formation of three-phase μEME, (iii) in-line extraction, (iv) flow-through optical detection of the acceptor phase, and (v) solvent removal and regeneration of the μEME device and fluidic lines. Using methylene blue (MB) as a model analyte, experimental results evinced that the 3D-printed channels with an obround cross-section (2.5 mm × 2.5 mm) were the most efficient in terms of absolute extraction recovery (59%), as compared to PTFE tubing of 2.5 mm inner diameter (27%). This is attributed to the distinctive convex interface of the organic phase (1-octanol), with a more pronounced laminar pattern, in 3D-printed SL methacrylate-based fluidic channels against that of PTFE tubing on account of the enhanced 1-octanol wettability and lower contact angles for the 3D-printed devices. The devices with obround channels were leveraged for the automatic μEME and in-line clean-up of MB in high matrix textile dyeing wastewater samples with relative recoveries ≥81%, RSD% ≤ 17.1% and LOD of 1.3 mg L-1. The 3D-printed nonsupported μEME device was proven superb for the analysis of wastewater samples with an elevated ionic strength (0.7 mol L-1 NaCl, 5000 mg L-1 Na2CO3, and 0.013 mol L-1 NaOH) with recorded electric currents below 12 μA.

NOVELTY

The coupling of 3D printing with nonsupported μEME in automatic flow-based systems is herein proposed for the first time and demonstrated for the clean-up of troublesome samples, such as wastewaters.

Layer-by-layer assembly of PDDA/MWCNTs thin films as an efficient strategy for extraction of organic compounds from complex samples

This article presents the assembly and characterization of poly(diallyldimethylammonium chloride)/multi-walled carbon nanotubes (PDDA/MWCNTs) thin films on borosilicate bottles using a layer-by-layer (LBL) approach. The thin films, consisting of 10 bilayers of coating materials, were thoroughly characterized using UV-VIS spectroscopy, scanning electron microscopy (SEM), and zeta potential measurements. The modified bottles were then utilized for the extraction of analytes with diverse acid-base characteristics, including drugs, illicit drugs, and pesticides, from saliva, urine, and surface water samples. The studied analytes can be adsorbed on the surface of the LBL film mainly through hydrogen bonding and/or hydrophobic interactions. Remarkably high extraction percentages of up to 92 % were achieved, accompanied by an impressive enhancement in the analytical signal of up to 12 times when the sample volume was increased from 0.7 to 10 mL. These results highlight the outstanding extraction and sorption capabilities of the developed material. Additionally, the (PDDA/MWCNTs)10 films exhibited notable resistance to extraction and desorption processes, enabling their reuse for at least 5 cycles. The straightforward and cost-effective fabrication of these sorbent materials using the LBL technique, combined with the ability to extract target compounds during sample transportation and/or storage, renders this sample preparation method a promising alternative.

Strategies for capillary electrophoresis: Method development and validation for pharmaceutical and biological applications-Updated and completely revised edition

This review is in support of the development of selective, precise, fast, and validated capillary electrophoresis (CE) methods. It follows up a similar article from 1998, Wätzig H, Degenhardt M, Kunkel A. "Strategies for capillary electrophoresis: method development and validation for pharmaceutical and biological applications," pointing out which fundamentals are still valid and at the same time showing the enormous achievements in the last 25 years. The structures of both reviews are widely similar, in order to facilitate their simultaneous use. Focusing on pharmaceutical and biological applications, the successful use of CE is now demonstrated by more than 600 carefully selected references. Many of those are recent reviews; therefore, a significant overview about the field is provided. There are extra sections about sample pretreatment related to CE and microchip CE, and a completely revised section about method development for protein analytes and biomolecules in general. The general strategies for method development are summed up with regard to selectivity, efficiency, precision, analysis time, limit of detection, sample pretreatment requirements, and validation.

Technological advances for analyzing the content of organ-on-a-chip by mass spectrometry

Three-dimensional (3D) cell cultures, including organ-on-a-chip (OOC) devices, offer the possibility to mimic human physiology conditions better than 2D models. The organ-on-a-chip devices have a wide range of applications, including mechanical studies, functional validation, and toxicology investigations. Despite many advances in this field, the major challenge with the use of organ-on-a-chips relies on the lack of online analysis methods preventing the real-time observation of cultured cells. Mass spectrometry is a promising analytical technique for real-time analysis of cell excretes from organ-on-a-chip models. This is due to its high sensitivity, selectivity, and ability to tentatively identify a large variety of unknown compounds, ranging from metabolites, lipids, and peptides to proteins. However, the hyphenation of organ-on-a-chip with MS is largely hampered by the nature of the media used, and the presence of nonvolatile buffers. This in turn stalls the straightforward and online connection of organ-on-a-chip outlet to MS. To overcome this challenge, multiple advances have been made to pre-treat samples right after organ-on-a-chip and just before MS. In this review, we summarised these technological advances and exhaustively evaluated their benefits and shortcomings for successful hyphenation of organ-on-a-chip with MS.

Green Method for the Selective Electromembrane Extraction of Parabens and Fluoroquinolones in the Presence of NSAIDs by Using Biopolymeric Chitosan Films

A chitosan biopolymeric membrane was successfully used as a support in a green electromembrane extraction procedure for the simultaneous and selective extraction of seven parabens and three fluoroquinolones in the presence of three non-steroidal anti-inflammatory drugs. The optimal experimental conditions (10 mL donor phase and 50 μL acceptor phase, pH 10 in both phases; 80 V of applied voltage during 15 min of extraction time) were determined, providing high enrichment factors for six of the studied parabens (EF ≥ 90) and the three fluoroquinolones (EF ≥ 50). Wide linear concentration ranges (0.5-500 μg L^-1), good linearity (>97%), low limits of detection (0.2-1.1 μg L^-1), and good repeatability (relative standard deviation values 4-10%) were achieved. The proposed method was successfully applied for the extraction of the target analytes from different kinds of water samples (river, lake, and swimming pool). The usage of a chitosan membrane in the extraction process presents many advantages, as it is a biodegradable and versatile support, offering a good alternative to commercial plastic materials commonly used in this methodology and these procedures.

An electromembrane microextraction-based green method for the determination of trace copper in natural waters

Driven by the search for an environmentally-friendly methodology, electromembrane extraction (EME) has recently emerged as a green and versatile tool for the analysis of trace pollutants in water samples, being mainly applied to the preconcentration and determination of organic compounds. Recently, EME has also shown its applicability to the analysis of inorganic species, allowing a considerable reduction in both reagent consumption and extraction times, and without loss of efficacy, in comparison with other liquid phase microextraction techniques. In this study, an EME system for trace copper analysis in natural waters has been optimised by the modified simplex method. A chemical modifier, di-2-pyridyl ketone benzoylhydrazone (dPKBH) was synthesized and dissolved in 1-nonanol, to be used as an organic phase impregnated into the pores of a polymeric hollow fibre. With only 15 min of extraction, an enrichment factor of 77.1 ± 10.8 was obtained for a wide salinity range (0-35), allowing its application in a variety of different waters, including seawater. Optimum operating conditions were a sample pH of 6.26, an electric potential of 95 V, 0.08 M nitric acid as the acceptor phase, 4.01 mM dPKBH in 1-nonanol as the organic phase and a stirring rate of 1500 rpm. A LOD of 0.004 μg L^-1 was obtained, and the system was successfully applied to the analysis of several water samples containing copper at low ppb levels (tap water and river water) or even at sub-ppb levels (seawater).

Analytical Performance of Electromembranes as a Tool for Nanoconcentrations of Silver in Waters

Electromembranes increase the efficiency of metal transport in liquid-phase microextraction systems by applying an electric potential, which accelerates the transport. Nevertheless, to get high extraction percentages in short extraction times it is necessary to take into account a great variety of factors, and multivariate optimization techniques are the best alternative to determine the most influential variables and to optimize the extraction process. In this work, a fractional factorial design was applied to determine the most influential variables in the extraction of silver by electromembranes. Thus, the effect of tri-isobutylphosphine sulphide (Cyanex 471x) concentration in the organic solution, sodium thiosulphate concentration in the acceptor solution, nitrate concentration in the sample solution, extraction time, stirring rate and electric potential on the enrichment factor were studied. Once the most important variables were selected, a small composite design (Draper-Lin) was used to obtain their optimal values to maximize the enrichment factor. Under these conditions, an experimental enrichment factor of 49.91 ± 3.95 was achieved after 22 min. Finally, the effect of saline matrix on the enrichment factor was tested and the optimized system was successfully applied to analyse silver concentrations at ultratrace levels, within the range of 7-29 ng·L^-1 in different real seawater samples.

Electromembrane extraction of tramadol from exhaled breath condensate and its liquid chromatographic analysis

Tramadol has extracted from the exhaled breath condensate (EBC) samples through the supported liquid membrane consisting of 2-nitrophenyl octyl ether impregnated in the hollow fiber wall, and the lumen of the hollow fiber was filled with 20 μL of an acceptor phase. Under the optimum conditions of the electromembrane extraction, i.e. the stirring speed of 750 rpm, extraction time of 20 min, acceptor pH at 1.0, donor phase pH at 6.0, and an applied voltage of 170 V across the supported liquid membrane, a preconcentration factor of 128-fold with a extraction recovery of 64% was achieved. Acceptable linearity was obtained in the tramadol concentration range of 5-1000 ng mL^-1 (R² = 0.9999) with a limit of detection of 1.5 ng mL^-1 and a limit of quantitation of 5 ng mL^-1. The relative standard deviations for the intra-day and inter-day replications were obtained between 0.4% and 2.5%. The validated technique was successfully used to determine tramadol in real EBC samples.