Electromembrane extraction combined with cyclodextrin-modified capillary electrophoresis for the quantification of trimipramine enantiomers

Liquid-Phase Microextraction Approaches for Preconcentration and Analysis of Chiral Compounds: A Review on Current Advances

Chirality is a critical issue in pharmaceutics, forensic chemistry, therapeutic drug monitoring, doping control, toxicology, or environmental investigations as enantiomers of a chiral compound can exhibit different activities, i.e., one enantiomer can have the desired effect while the other one can be inactive or even toxic. To monitor enantioselective metabolism or toxicokinetic/toxicodynamic mechanisms in extremely low content in biological or environmental matrices, sample preparation is vital. The present review describes current status of development of liquid-phase microextraction approaches such as hollow fiber liquid-phase microextraction (HF-LPME), electromembrane extraction (EME), dispersive liquid-liquid microextraction (DLLME), and supramolecular solvent-based microextraction (SSME), used for sample preparation of enantiomers/chiral compounds. The advantages and limitations of the above techniques are discussed. Attention is also focused on chiral separation approaches commonly applied to study the stereo-selective metabolism or toxicokinetic/toxicodynamic mechanisms of enantiomers in the biological and environmental samples.

Volatile free liquid membranes for electromembrane extraction

Volatile solvents are excellent extraction media for liquid-liquid extractions. However, their use in supported liquid membranes (SLMs) is limited by their evaporation from SLM and thus poor SLM stability and they have never been considered truly useful for electromembrane extraction (EME). In this contribution, volatile solvents were systematically investigated as liquid membranes for EME and their extraction characteristics were comprehensively examined for the first time. A short plug of a water immiscible volatile solvent (a free liquid membrane (FLM)) was sandwiched between two aqueous plugs (donor and acceptor solutions) in a narrow-bore polymeric tubing. Evaporation of the volatile FLM was thus completely avoided and excellent stability of the phase interface was ensured. Suitability of volatile FLMs for EMEs was justified by μ-EMEs of nortriptyline, haloperidol, loperamide and papaverine as model non-polar basic drugs. Extraction performance of μ-EME through ethyl acetate was comparable or better to that through standard non-volatile EME solvents and a high extraction selectivity was achieved for nortriptyline and haloperidol extracted through chloroform. μ-EMEs through the volatile FLMs were characterized by high extraction recoveries (62%-99% for standards and 40-89% for body fluids), low electric currents (10-1380 nA), no susceptibility to matrix ions and suitability for pretreatment of raw body fluids (human urine and serum). Resulting extracts were analysed by capillary electrophoresis with ultraviolet detection (CE/UV). Repeatability of the μ-EME-CE/UV method was excellent with intra-day and inter-day RSD values 0.8-3.2% and 1.8-4.6%, respectively. Further experiments demonstrated additional advantages of volatile FLMs by nearly exhaustive μ-EMEs of atenolol as the polar basic drug with no need for FLM modification by ionic carriers. The presented comprehensive examination of volatile solvents has broadened the range of liquid membranes suitable for EME and it is believed that this proof-of-concept study will stimulate further interest in a deeper investigation of volatile phase interfaces in EME.

A low-voltage electro-membrane extraction for quantification of imatinib and sunitinib in biological fluids

Aim: Hollow-fiber-based supported liquid membrane was modified utilizing nanostructures such as graphite, graphene oxide or nitrogen-doped graphene oxide, for electro-membrane extraction (EME) of imatinib and sunitinib from biological fluids. By applying these conductive nanostructures, a low-voltage EME device (6.0 V) was fabricated. Materials & methods: A response surface methodology through central composite design was used to evaluate and optimize effects of various essential factors that influence on normalized recovery. Results: Optimal extraction conditions were set as, 1-octanol with 0.01 % (w/v) graphene oxide functioning as the supported liquid membrane, an extraction time of 17.0 min, pH of the acceptor and the donor phase of 2.8 and 7.9, respectively. Conclusion: The method was successfully applied to quantify imatinib and sunitinib in biological fluids.

Impact of ion balance in electromembrane extraction

Electromembrane extraction (EME) involves transfer of analyte ions from aqueous sample, through a supported liquid membrane (SLM), and into an aqueous acceptor solution under the influence of an external electrical field. In addition to target analyte ions, the sample also contains matrix ions, and both the sample and acceptor contains background buffer ions to control pH. The ratio between the total amount of ions in sample and acceptor defines the ion balance (χ). Previous publications have discussed the impact of ion balance, but conclusions are contradictory. Therefore, the current paper investigated the ion balance in more detail. From a theoretical point of view, low χ-values favor EME; buffer anions at high concentration in the acceptor migrate into the SLM, while target cations enters the SLM from the sample to maintain electroneutrality. A large number of experiments was performed in this paper to investigate the practical impact of ion balance. Twelve basic drugs were used as model analytes (0.0 < log P < 5.0), and 2-nitrophenyl octyl ether (NPOE) and NPOE + 5% di(2-ethylhexyl) phosphate (DEHP) were used as SLM. With formate buffer pH 3.75 as sample and acceptor, the impact of χ in the range 0.01-10 was studied without bias from differences in pH. Here model analytes were unaffected by ion balance. Buffers containing propionic, butyric, and valeric acid were also tested. These buffer ions migrated more into the SLM, and affected recoveries in several cases. However, this was due to ion pairing rather than effects of ion balance. Similar behaviors from sodium chloride and urine samples were observed with different χ-values. Thus, in the systems tested, almost no impact of ion balance was found, and this was attributed to very low partition of background buffer and matrix ions into the SLM. On the other hand, extractions were in several cases influenced by ion pairing phenomena.

Inside gel electromembrane extraction: A novel green methodology for the extraction of morphine and codeine from human biological fluids

In this work, a new mode of gel-electromembrane extraction (G-EME), called "inside" gel-EME (IG-EME) is proposed for the extraction of morphine and codeine as model basic drugs from complex biological samples. Here, an aqueous media that was captured inside the agarose gel membrane, acted as both gel membrane and the acceptor phase (AP) at the same time. In this regard, the membrane served as the separation filter (membrane) and supported liquid acceptor phase (SLAP) as well. With this new development, unwanted changes of the AP volume during the extraction, which is a common issue in the G-EME (due to electroendosmosis (EEO) phenomenon), was addressed properly. Briefly, the setup involved insertion of negative electrode inside the gel membrane and positive electrode into the donor phase (DP). Following that, the IG-EME was easily performed using optimal conditions (pH of the DP: 6.0; membrane composition (agarose concentration: 1% (w/v) in aqueous media with pH 3.0, and 15 mm thickness); voltage: 25 V; and extraction time: 30 min). After extraction, the agarose gel was withdrawn and centrifuged for 5 min with 12000 rpm, to disrupt its framework to release the "trapped aqueous AP" apart from the gel structure. The separated AP was finally injected into the HPLC-UV for the analysis. The limits of detection (LODs) and recoveries in this proposed method were obtained 1.5 ng mL^-1 and 67.7 %-73.8 %, respectively. The system feasibility was examined by the quantification of model drugs in the real plasma and urine samples.

Enantiomeric Determination of Drugs in Pharmaceutical Formulations and Biological Samples by Electrokinetic Chromatography

Chirality is a relevant issue in the pharmaceutical field due to the different biological activity that enantiomers of a chiral drug can show. In fact, the desired biological or pharmaceutical activity might be present in only one of the enantiomers, while the other enantiomer(s) may have different biological activity, be inactive or even toxic. This has motivated in recent years the development of drugs marketed as pure enantiomers to avoid exposing the organism to the action of enantiomers that may not be active or even harmful to health. Thus, it is of high interest to develop enantioselective analytical methodologies to control the presence of enantiomeric impurities and to understand the enantioselective metabolism of chiral drugs. This review gives an overview about the analytical strategies developed by electrokinetic chromatography (EKC) from 2010 to June 2019 for the enantiomeric determination of drugs in both pharmaceutical formulations and biological samples. The types of chiral selectors used, the migration order of enantiomers, their resolution, the detection technique employed and the sensitivity achieved are revised and compared. Also, applications to assess the enantiomeric purity control of pharmaceutical formulations and to determine chiral drugs in biological samples to study their metabolism are included. Advantages and limitations of the chiral methods developed by EKC are also discussed.

Application of polyacrylamide gel as a new membrane in electromembrane extraction for the quantification of basic drugs in breast milk and wastewater samples

Introducing new membranes with green chemistry approach seems to be a great challenge for the development of a practical method in separation science. In this regard, for the first time, polyacrylamide gel as a new membrane in electromembrane extraction (EME) was used for the extraction of three model basic drugs (pseudoephedrine (PSE), lidocaine (LID), and propranolol (PRO)), followed by HPLC-UV. In comparison with conventional EME, in this method neither organic solvent nor carrier agents were used for extraction of mentioned drugs. Different variables for fabrication of polyacrylamide gel and extraction process were evaluated. Polyacrylamide gel (containing 12% (w/v) acrylamide, and 3.0% (w/w) bisacrylamide) with 2 mm thickness at pH = 1.5 was fabricated as membrane. The drugs were extracted from aqueous samples, through a polyacrylamide gel membrane, to an aqueous acceptor phase on membrane. Under the optimized extraction conditions (Voltage: 85 V, extraction time: 28 min, acceptor phase's pH: 4.0, and donor phase's pH: 7.0) limits of quantification and detection were in the ranges of 1.0-20.0 ng mL^-1 and 0.3-6.0 ng mL^-1, respectively. Applying the proposed method to determine and quantify intended drugs in breast milk, and wastewater samples have revealed acceptable results.

Initial fate assessment of teratogenic drug trimipramine and its photo-transformation products - Role of pH, concentration and temperature

Trimipramine (TMP) is an antidepressant drug used for the treatment of a variety of depressive states and other psychiatric disorders. It has been already detected in the aquatic environment. Currently, no further knowledge is available on fate and effects of TMP in the aquatic environment. Therefore, we studied the biodegradability of TMP and of its photolysis transformation products (PTPs) generated by irradiation with polychromatic UV light in aqueous solution. Different conditions including initial drug concentration, pH, and temperature were applied during TMP photolysis. Subsequently, the time courses of TMP and dissolved organic carbon (DOC) concentrations were monitored throughout the whole photo-degradation process. Then, high-resolution mass spectrometry was used to identify and elucidate the structures of the resulting PTPs. After that, the two standardized biodegradation tests, Closed Bottle test (CBT; OECD 301 D) and Manometric Respirometry test (MRT; OECD 301 F), were performed for TMP and its photolytic mixtures to assess the biodegradability of TMP and its PTPs. Finally, the toxicity of TMP and its photolytic mixtures was predicted using different quantitative structure activity relationship (QSAR) software. It was found that after 128 min of UV-irradiation, 91.8% of TMP at the initial concentration of 100 mg L^-1 was eliminated with only 23.9% removal in the DOC. So, it can be pointed out that more than 65% of the degraded TMP is transformed to new non-mineralized PTPs. 14 new PTPs were detected in TMP's photolytic mixtures. Their supposed structures indicate that the proposed photo-transformation pathway is mainly by hydroxylation. The statistical analysis confirms that the differences in the degradation rates of TMP as a function of concentration, pH, and temperature are statistically significant in most cases investigated here. In biodegradation testing, TMP and its PTPs are classified as not readily biodegradable, while LC-MS analysis revealed some PTPs to be eliminated more than TMP itself. Results from QSAR analysis confirmed that some of the PTPs could be biodegradable, and revealed that some of the non-biodegradable PTPs may be human and/or eco-toxic, posing a risk to the environment. Our findings show that TMP under UV-irradiation could lead to the formation of some more easily biodegradable PTPs and some others toxic and non-biodegradable PTPs. Therefore, further studies should be conducted regarding the fate and effects of TMP and its PTPs elucidated in this study on human health and on the environment.

Electrically stimulated liquid-based extraction techniques in bioanalysis

Sample preparation is a vital and inseparable part of an analytical procedure. This issue has motivated the analytical research community around the world to develop new, fast and cost-effective extraction methods which can eliminate interfering substances, provide high preconcentration factors and increase the determination sensitivity. Electrical field induced extraction technique is a topic that has received major attention in recent years. This fact can be attributed to the considerable advantages provided by imposition of an electrical driving force especially control of different properties of an extraction system such as selectivity, cleanup, rate and efficiency. In this review, focus is centered on the electrical field induced liquid phase extraction techniques and their potential for bioanalysis.

Rotating electrode in electro membrane extraction: a new and efficient methodology to increase analyte mass transfer

Rotating electrode electromembrane extraction (REEME) as a new EME approach was introduced for the extraction of basic drugs from different matrices.

Evaluation of three dimensional high nitrogen doped graphene as an efficient sorbent for the preconcentration of BTEX compounds in environmental samples

A simple and highly sensitive method that involves SPE-GC with three dimensional high nitrogen doped graphene as a novel sorbent used for determination of BTEX compounds in environmental samples.

Application of pH-sensitive magnetic nanoparticles microgel as a sorbent for the preconcentration of phenoxy acid herbicides in water samples

Introducing new sorbents is an interesting and debatable issue in the field of sample preparation. In this study, for the first time, a pH-sensitive magnetic nanoparticles microgel, Fe3O4-SiO2-oly(4-vinylpyridine), was introduced as a new sorbent. The operating mechanism of this sorbent is based on changing the pH value of the sample and consequently the structure of this pH-sensitive microgel is changed. So that, at pH 6.0 the microgel was ready to accept and load the analytes (partial swelling), and when the pH was increased to 8.0, the microgel was closed and analytes were trapped inside the sorbent (deswelling). At pH 2.0 the microgel was opened and the analytes were released from the microgel (swelling). As the adsorption and desorption mechanism is based on changing the pH and only aqueous medium is used as the effluent solvent, this method is introduced as a green extraction method. The use of this microgel resulted in excellent figures of merit. The limits of quantitation and detection for herbicides were obtained within the range of 10-30 and 3-10 ng mL(-1), respectively. Finally, the proposed method was successfully applied to determine the concentration of phenoxy acid herbicides as hazardous materials in water samples.

The potential of electromembrane extraction for bioanalytical applications

Modern requirements in the field of bioanalysis often involve miniaturized, high-throughput sample preparation techniques that consume low amounts of both sample and potentially hazardous organic solvents. Electromembrane extraction is one technique that meets several of these requirements. In this principle analytes are selectively extracted from a biological matrix, through a supported liquid membrane and into an aqueous acceptor solution. The whole extraction process is facilitated by an electric field across the supported liquid membrane, which greatly reduces the extraction time. This review will give a thorough overview of recent advances in bioanalytical applications involving electromembrane extraction, and discuss both possibilities and challenges of the technique in a bioanalytical setting.

Evaluation of sulfated maltodextrin as a novel anionic chiral selector for the enantioseparation of basic chiral drugs by capillary electrophoresis

Introducing a new class of chiral selectors is an interesting work and this issue is still one of the hot topics in separation science and chirality. In this study, for the first time, sulfated maltodextrin (MD) was synthesized as a new anionic chiral selector and then it was successfully applied for the enantioseparation of five basic drugs (amlodipine, hydroxyzine, fluoxetine, tolterodine, and tramadol) as model chiral compounds using CE. This chiral selector has two recognition sites: a helical structure and a sulfated group which contribute to three corresponding driving forces; inclusion complexation, electrostatic interaction, and hydrogen binding. Under the optimized condition (buffer solution: 50 mM phosphate (pH 3.0) and 2% w/v sulfated MD; applied voltage: 18 kV; temperature: 20°C), baseline enantioseparation was observed for all mentioned chiral drugs. When instead of sulfated MD neutral MD was used under the same condition, no enantioseparation was observed which means the resolution power of sulfated MD is higher than neutral MD due to the electrostatic interaction between sulfated groups and protonated chiral drugs. Also, the countercurrent mobility of negatively charged MD (sulfated MD) allows more interactions between the chiral selector and chiral drugs and this in turn results in a successful resolution for the enantiomers. Furthermore, a higher concentration of neutral MD (approximately five times) is necessary to achieve the equivalent resolution compared with the negatively charged MD.

Maltodextrins as chiral selectors in CE: molecular structure effect of basic chiral compounds on the enantioseparation

Prediction of chiral separation for a compound using a chiral selector is an interesting and debatable work. For this purpose, in this study 23 chiral basic drugs with different chemical structures were selected as model solutes and the influence of their chemical structures on the enantioseparation in the presence of maltodextrin (MD) as chiral selector was investigated. For chiral separation, a 100-mM phosphate buffer solution (pH 3.0) containing 10% (w/v) MD with dextrose equivalent (DE) of 4-7 as chiral selector at the temperature of 25°C and voltage of 20 kV was used. Under this condition, baseline separation was achieved for nine chiral compounds and partial separation was obtained for another six chiral compounds while no enantioseparation was obtained for the remaining eight compounds. The results showed that the existence of at least two aromatic rings or cycloalkanes and an oxygen or nitrogen atom or -CN group directly bonded to the chiral center are necessary for baseline separation. With the obtained results in this study, chiral separation of a chiral compound can be estimated with MD-modified capillary electrophoresis before analysis. This prediction will minimize the number of preliminary experiments required to resolve enantiomers and will save time and cost.

Electromembrane extraction--three-phase electrophoresis for future preparative applications

The purpose of this article is to discuss the principle and the future potential for electromembrane extraction (EME). EME was presented in 2006 as a totally new sample preparation technique for ionized target analytes, based on electrokinetic migration across a supported liquid membrane under the influence of an external electrical field. The principle of EME is presented, and typical performance data for EME are discussed. Most work with EME up to date has been performed with low-molecular weight pharmaceutical substances as model analytes, but the principles of EME should be developed in other directions in the future to fully explore the potential. Recent research in new directions is critically reviewed, with focus on extraction of different types of chemical and biochemical substances, new separation possibilities, new approaches, and challenges related to mass transfer and background current. The intention of this critical review is to give a flavor of EME and to stimulate into more research in the area of EME. Unlike other review articles, the current one is less comprehensive, but put more emphasis on new directions for EME.

Electrical field-induced extraction and separation techniques: promising trends in analytical chemistry--a review

Sample preparation is an important issue in analytical chemistry, and is often a bottleneck in chemical analysis. So, the major incentive for the recent research has been to attain faster, simpler, less expensive, and more environmentally friendly sample preparation methods. The use of auxiliary energies, such as heat, ultrasound, and microwave, is one of the strategies that have been employed in sample preparation to reach the above purposes. Application of electrical driving force is the current state-of-the-art, which presents new possibilities for simplifying and shortening the sample preparation process as well as enhancing its selectivity. The electrical driving force has scarcely been utilized in comparison with other auxiliary energies. In this review, the different roles of electrical driving force (as a powerful auxiliary energy) in various extraction techniques, including liquid-, solid-, and membrane-based methods, have been taken into consideration. Also, the references have been made available, relevant to the developments in separation techniques and Lab-on-a-Chip (LOC) systems. All aspects of electrical driving force in extraction and separation methods are too specific to be treated in this contribution. However, the main aim of this review is to provide a brief knowledge about the different fields of analytical chemistry, with an emphasis on the latest efforts put into the electrically assisted membrane-based sample preparation systems. The advantages and disadvantages of these approaches as well as the new achievements in these areas have been discussed, which might be helpful for further progress in the future.

A new platform for sensing urinary morphine based on carrier assisted electromembrane extraction followed by adsorptive stripping voltammetric detection on screen-printed electrode

Electromembrane extraction (EME) coupled with electrochemical detection on screen-printed carbon electrode has been developed for the quantification of morphine in urine samples. Charged morphine molecules were extracted from an aqueous sample by applying an electrical potential through a thin supported liquid membrane (SLM) into an acidic aqueous acceptor solution (20 µL) placed inside the lumen of a hollow fiber. Then, the acceptor solution was mixed with 20 µL of NaOH solution (0.1 M) and analyzed using screen printed electrochemical strip. Differential pulse voltammetry (DPV) peak current at 0.18 V was selected as the signal and the influences of experimental parameters were investigated and optimized using Box-behnken design and also one-variable-at-a-time methodology as follows: adsorptive accumulation time, 40 s; SLM, 2-nitrophenyl octyl ether+10% tris-(2-ethylhexyl) phosphate+10% di-(2-ethylhexyl) phosphate; pH of the sample solution, 6.0; pH of the acceptor solution, 1.0; EME time, 24 min; EME potential, 90 V and stirring rate, 1000 rpm. The calibration curve which was plotted by the variation of DPV currents as a function of morphine concentration was linear within the range of 0.005-2.0 µg mL(-1). The limit of detection and the limit of quantification were 0.0015 (S/N=3) and 0.005 µg mL(-1), respectively. Finally, the proposed method was able to determine morphine simply and effectively at concentration levels encountered in toxicology and doping.

Electromembrane extraction--a novel extraction technique for pharmaceutical, chemical, clinical and environmental analysis

Electromembrane extraction (EME) is a novel sample preparation technique in pharmaceutical, chemical, clinical and environmental analysis. This technique uses electromigration across artificial liquid membranes for selective extraction of analytes and sample enrichment from complex matrices. This review focuses on the setup, general procedure and parameters affecting the extraction efficiency of EME. An overview of innovations in EME (on-chip EME, low voltage EME, drop-to-drop EME, pulsed EME and EME followed by low-density solvent based ultrasound-assisted emulsification microextraction) is also presented in this article and attention is focused on the use of EME for pharmaceutical, chemical, clinical and environmental analysis.