Electromembrane extraction of polar substances - Status and perspectives

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.

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.

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.

The selective extraction of dietary polyamines from chicken breast using the application of a lab-on-a-chip electromembrane and dispersive liquid-liquid microextraction followed by gas chromatography-mass spectrometry

Excessive dietary polyamines (PAs), including putrescine (PUT), spermine (SPM), and spermidine (SPD), have become a worldwide concern due to their carcinogenicity and reduced shelf life. A modern miniaturized on-chip electromembrane extraction (EME) has been applied to extract these compounds from chicken breast samples. This method is based fundamentally on ionic compounds' electrostatic attraction, diffusion, and solubility in the acceptor phase. The chemical structure of polyamines enables their efficient extraction using an electric driving force on a microchip device. HCl solution (0.1 mol L-1) was applied as an aqueous acceptor solvent. Dispersive liquid-liquid microextraction was performed after EME to facilitate joining three-phase EME to GC-MS and improve the merit figures. The total ranges of 3.77-7.89 μg g-1, 3.48-7.02 μg g-1, and 0.78-2.20 μg g-1 were acquired as PUT, SPM and SPD concentrations in chicken breast, respectively. The results demonstrate that the level of PAs in fresh chicken breast samples is not concerning, but it may reduce the quality of chicken meat over time. This novel analytical technique has several advantages: high recovery, substantial quickness, remarkable selectivity, and good enrichment factors. This emerging method could be generalized to other studies to analyze different foodstuffs.

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.

Electromembrane extraction - capillary zone electrophoresis for the quantitative determination of β-lactam antibiotics in milk samples

Three penicillin-based β-lactam antibiotics (benzylpenicillin, amoxicillin, and ampicillin) were extracted by electromembrane extraction (EME) and determined in the resulting extracts by capillary zone electrophoresis (CZE) with UV-Vis detection. The EME was optimized for the simultaneous clean-up of complex samples and preconcentration of the three antibiotics and employed 1-octanol as the organic phase interface (impregnated in the pores of a hollow fiber), acidified donor solution (pH 3), and phosphate buffer (pH 5.6) as the acceptor solution. The EMEs were carried out for 20 min at 300 V and constant stirring (750 rpm) of the donor solution. At the optimized EME-CZE conditions, the sensitivity of the analytical method was sufficient for the determination of the three β-lactam antibiotics in undiluted cow's milk at concentrations below the EU maximum residue limits (4 μg/L) in foodstuffs. The method was simple, rapid, and convenient and offered extraction recoveries of 13.5 - 87.3 %, enrichment factors of 23.6 - 152.8, repeatability (RSD values) better than 7.6 %, linear analytical response in the 1 - 100 μg/L (3 - 100 μg/L for benzylpenicillin) concentration range with correlation coefficients ≥ 0.9997, and limits of detection from 0.2 to 1.2 μg/L. The proposed analytical concept was used for the rapid control of milk quality (i.e. assessment of excessive use of antibiotics in dairy animals), moreover, it was further extended to the trace determination of β-lactam antibiotics in other complex samples, such as in wastewater.

Electromembrane extraction of peptides based on hydrogen bond interactions

BACKGROUND

Electromembrane extraction (EME) of peptides reported in the scientific literature involve transfer of net positively charged peptides from an aqueous sample, through a liquid membrane, and into an aqueous acceptor solution, under the influence of an electrical field. The liquid membrane comprises an organic solvent, containing an ionic carrier. The purpose of the ionic carrier is to facilitate peptide solvation in the organic solvent based on ionic interactions. Unfortunately, ionic carriers increase the conductivity of the liquid membrane; the current in the system increases, the electrolysis in sample and acceptor is accelerated, and the extraction system tend to be unstable and suffers from drifting pH.

RESULTS

In the present work, a broad selection of organic solvents were tested as pure liquid membrane for EME of peptides, without ionic carrier. Several phosphates provided high mass transfer, and tri(pentyl) phosphate was selected since this solvent also provided high operational stability. Among 16 different peptides used as model analytes, tri(pentyl) phosphate extracted those with net charge +1 and with no more than two polar side chains. Tri(pentyl) phosphate served as a very strong hydrogen bond acceptor, while the protonated peptides were hydrogen bond donors. By such, hydrogen bonding served as the primary interactions responsible for mass transfer. Tri(pentyl) phosphate as liquid membrane, could exhaustively extract leu-enkephalin, met-enkephalin, and endomorphin from human blood plasma and detected by LC-MS/MS. Calibration curves were linear (r² > 0.99) within a concentration range from 1 to 500 ng/mL, and a relative standard deviation within 12% was observed for precision studies.

SIGNIFICANCE

The current experiments are important because they indicate that small peptides of low polarity may be extracted selectively in EME based on hydrogen bond interactions, in systems not suffering from electrolysis.

Ultrasound assisted membrane-assisted solvent extraction for the simultaneous assessment of some drugs involved in drug-facilitated sexual assaults by liquid chromatography-tandem mass spectrometry

A simple and highly efficient ultrasound assisted membrane-assisted solvent extraction (MASE) pre-treatment method for urine has been developed and validated for the simultaneous determination of twenty-two drugs involved in drug-facilitated sexual assaults (DFSAs) by liquid chromatography-tandem mass spectrometry. MASE was performed with 4.0 mL of urine (pH adjusted at 12), 400 μL of hexane as an organic solvent inside the polypropylene membrane, and ultrasonication (45 kHz, 120 W) for 10 min. A pre-concentration factor of 40 was achieved after evaporation (N2 stream) and re-dissolution in 100 µL of methanol. Analytes were separated using a Zorbax Eclipse Plus C18 column under gradient elution with aqueous 10 mM NH4HCO3 (pH 8.0) and methanol as mobile phases. Matrix-matched calibrations allowed the assessment of DFSA drugs of quite different octanol-water partition coefficients (Ko/w), from 1.32 101 for pregabalin to 2.45 105 for clomipramine (Log P values from 1.12 (pregabalin) to 5.39 (clomipramine)). The limit of detection (LOD) was between 0.0075 to 0.37 µg L-1, with analytical recoveries ranging from 73 to 103%, and relative standard deviations (RSDs) within the 2-20% range. The applicability of the method was demonstrated after analysing urine samples under forensic investigation.

Conductive vial electromembrane extraction of opioids from oral fluid

The use of oral fluid as sample matrix has gained significance in the analysis of drugs of abuse due to its non-invasive nature. In this study, the 13 opioids morphine, oxycodone, codeine, O-desmethyl tramadol, ethylmorphine, tramadol, pethidine, ketobemidone, buprenorphine, fentanyl, cyclopropylfentanyl, etonitazepyne, and methadone were extracted from oral fluid using electromembrane extraction based on conductive vials prior to analysis with ultra-high performance liquid chromatography-tandem mass spectrometry. Oral fluid was collected using Quantisal collection kits. By applying voltage, target analytes were extracted from oral fluid samples diluted with 0.1% formic acid, across a liquid membrane and into a 300 μL 0.1% (v/v) formic acid solution. The liquid membrane comprised 8 μL membrane solvent immobilized in the pores of a flat porous polypropylene membrane. The membrane solvent was a mixture of 6-methylcoumarin, thymol, and 2-nitrophenyloctyl ether. The composition of the membrane solvent was found to be the most important parameter to achieve simultaneous extraction of all target opioids, which had predicted log P values in the range from 0.7 to 5.0. The method was validated in accordance to the guidelines by the European Medical Agency with satisfactory results. Intra- and inter-day precision and bias were within guideline limits of ± 15% for 12 of 13 compounds. Extraction recoveries ranged from 39 to 104% (CV ≤ 23%). Internal standard normalized matrix effects were in the range from 88 to 103% (CV ≤ 5%). Quantitative results of authentic oral fluid samples were in accordance with a routine screening method, and external quality control samples for both hydrophilic and lipophilic compounds were within acceptable limits.

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.

Smartphone-controlled biosensor for viral respiratory infectious diseases: Screening and response

Outbreaks of emerging viral respiratory infectious diseases (VRIDs) including coronavirus disease 2019 (COVID-19) seriously endanger people's health. However, the traditional nucleic acid detection required professionals and larger instruments and antigen-antibody detection suffered a long window period of target generation. To facilitate the VRIDs detection in time for common populations, a smartphone-controlled biosensor, which integrated sample preparation (electromembrane extraction), biomarker detection (red-green-blue model) and remote response technology (a built-in APP), was developed in this work. With the intelligent biosensor, VRIDs could be recognized in the early stage by using endogenous hydrogen sulfide as the biomarker. Importantly, it only took 15 min to accomplish the whole process of screening and response to VRIDs. Moreover, the experimental data showed that this smartphone-controlled biosensor was suitable for ordinary residents and could successfully differentiate non-communicable respiratory diseases from VRIDs. To the best of our knowledge, this is the first time that a smartphone-controlled biosensor for screening and response to VRIDs was reported. We believe that the present biosensor will help ordinary residents jointly deal with the challenges brought by COVID-19 or other VRIDs in the future.

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).

Electrokinetic Extraction of Doxorubicin from Biological Fluids by Polymer Inclusion Membrane Sampling Probe

A polymer inclusion membrane (PIM) based sampling probe was developed for electrokinetic extraction of drugs from biological fluids. The probe was fabricated by dip-coating a nonconductive glass capillary tube in a homogeneous PIM solution for three cycles. The PIM solution comprised cellulose triacetate (CTA), 2-nitrophenyl octyl ether (NPOE), and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide [EMIM][NTf₂] in a ratio of 5:4:2. The developed probe electrokinetically extracted doxorubicin from human plasma, human serum, and dried blood spot (DBS). The practicability and reliability of the electrokinetic extraction were evaluated by LC-MS/MS to quantify the desorption of extracted doxorubicin. Under the optimized conditions, a quantification limit of 0.2-2 ng/mL was achieved for the three biological samples. The probe was further integrated into a portable battery-powered device for safe low-voltage (36 V) electrokinetic extraction. The developed technique is envisioned to provide a more efficient analytical workflow in the laboratory.

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.