The low conductivity of separation electrolytes employed in nonaqueous capillary electrophoresis (NACE) limits the use of on-line sample concentration or stacking by field enhancement. Herein, micelle-to-solvent stacking (MSS) was performed by the simple injection of a micellar solution plug prior to electrokinetic injection of sample prepared under field-enhanced stacking conditions (known as field-enhanced sample injection, FESI). The proposed approach allowed a 214-625-fold improvement in peak signals for targeted anticancer drugs (e.g., tamoxifen) and its major metabolites in NACE using 100% methanol-based separation electrolyte that comprised of 7.5mM deoxycholic acid sodium salt, 15mM acetic acid and 1mM 18-crown-6. These improvements yielded tamoxifen and its metabolites with 2-5 times better stacking efficiency as compared to those obtained without micellar solution injection or FESI only. This is comparable to the results typically achieved when FESI is combined with isotachophoresis (electrokinetic supercharging). The FESI-MSS-NACE was tested for the measuring levels of target drugs in plasma. The analytical figures of merit are also reported.
A method for on-line matrix elimination to enable selective quantification of ultraviolet absorbing analytes by a flow-injection analysis procedure is described. Selectivity is achieved by electric field driven extraction across a polymer inclusion membrane. The method was demonstrated on the example of the determination of naproxen from spiked human urine. Membranes of 10 μm thickness were employed which consisted of 7.5 mg cellulose triacetate as base polymer, 5 mg of o-nitrophenyl octyl ether as plasticizer and 7.5 mg of Aliquat 336 as cationic carrier. Ten μL of sample was introduced into a continuous stream of background solution consisting of 100 µM aqueous NaClO₄ with a flow rate of 2 μL/min while applying a voltage of 150 V to the extraction cell. The target ion was electrokinetically transported across the membrane and enriched in 1.5 μL of a stagnant acceptor solution. This was subsequently pumped past a flow-through UV detector for quantification. The method showed a linear range from 5 to 200 µM with a correlation coefficient of 0.9978 and a reproducibility of typically 7% (n = 8). The detection limit of the method for naproxen was 2 µM.
Drug-drug cocrystalllization is a novel mechanism for effective pharmacological combination therapy. In this work, we have demonstrated the preparation of a drug-drug cocrystal of a hypertension drug (Telmisartan; TEL) with a hyperuricemia drug (Febuxostat; FEB) in 1:1 molar ratio using a solvent evaporation method for the first time. Generally, a multi-component system may yield either a eutectic, salt, and/or a cocrystal. This study adopted a methodical orthogonal framework to analyze the final solid form. A single crystal X-ray structural investigation revealed the formation of a heterosynthon with carboxylic and benzimidazole groups of FEB and TEL, respectively, in the triclinic P-1 space group. ΔpKa of the heterosynthon is ∼1.5, hence, based on the empirical rules, a salt-cocrystal continuum is hypothesized. Further, attenuated total reflectance Fourier transform infrared (ATR-FTIR), and Raman spectroscopy were employed to corroborate the hydrogen bond formation in the heterosynthon (-N---H-O-), which confirmed the propensity for cocrystal formation. An accelerated stability study and an in vitro biorelevant dissolution study of the cocrystal were performed, which demonstrated that it is physiochemically stable, but it resulted in a slower dissolution rate when compared with plain drugs.
A sample pre-treatment method based on a dynamic mixed matrix membrane tip extraction followed by capillary electrophoresis with contactless conductivity detection (CE-C4D) was evaluated for the determination of tobramycin in human plasma. The extraction tip device consisted of a cellulose triacetate membrane tip wall immobilised with 15% (w/w) of hydrophilic lipophilic balance (HLB) nanoparticles as adsorbent. The extraction was performed dynamically by withdrawing/dispensing the plasma sample through the tip device followed by desorption into 20 μL of acidified aqueous solution at pH 3 prior to the CE-C4D analysis. Under the optimum conditions, the detection limit of the method for tobramycin was 10 ng/mL, with intraday and interday repeatability RSDs of 3.5% and 4.5%, respectively. Relative recoveries in spiked human plasma were 99.6%-99.9%. The developed approach was successfully demonstrated for the quantification of tobramycin in human plasma samples.
A dynamic supported liquid membrane tip extraction (SLMTE) procedure for the effective extraction and preconcentration of glyphosate (GLYP) and its metabolite aminomethylphosphonic acid (AMPA) in water has been investigated. The SLMTE procedure was performed in a semi-automated dynamic mode and demonstrated a greater performance against a static extraction. Several important extraction parameters such as donor phase pH, cationic carrier concentration, type of membrane solvent, type of acceptor stripping phase, agitation and extraction time were comprehensively optimized. A solution of Aliquat-336, a cationic carrier, in dihexyl ether was selected as the supported liquid incorporated into the membrane phase. Quantification of GLYP and AMPA was carried out using capillary electrophoresis with contactless conductivity detection. An electrolyte solution consisting of 12 mM histidine (His), 8 mM 2-(N-morpholino)ethanesulfonic acid (MES), 75 microM cetyltrimethylammonium bromide (CTAB), 3% methanol, pH 6.3, was used as running buffer. Under the optimum extraction conditions, the method showed good linearity in the range of 0.01-200 microg/L (GLYP) and 0.1-400 microg/L (AMPA), acceptable reproducibility (RSD 5-7%, n=5), low limits of detection of 0.005 microg/L for GLYP and 0.06 microg/L for AMPA, and satisfactory relative recoveries (90-94%). Due to the low cost, the SLMTE device was disposed after each run which additionally eliminated the possibility of carry-over between runs. The validated method was tested for the analysis of both analytes in spiked tap water and river water with good success.
A novel microextraction technique termed solid phase membrane tip extraction (SPMTE) was developed. Selected triazine herbicides were employed as model compounds to evaluate the extraction performance and multiwall carbon nanotubes (MWCNTs) were used as the adsorbent enclosed in SPMTE device. The SPMTE procedure was performed in semi-automated dynamic mode and several important extraction parameters were comprehensively optimized. Under the optimum extraction conditions, the method showed good linearity in the range of 1-100 microg/L, acceptable reproducibility (RSD 6-8%, n=5), low limits of detection (0.2-0.5 microg/L), and satisfactory relative recoveries (95-101%). The SPMTE device could be regenerated and reused up to 15 analyses with no analyte carry-over effects observed. Comparison was made with commercially available solid phase extraction-molecular imprinted polymer cartridge (SPE-MIP) for triazine herbicides as the reference method. The new developed method showed comparable or even better results against reference method and is a simple, feasible, and cost effective microextraction technique.
A new sample pre-treatment technique termed cone-shaped membrane liquid phase microextraction (CSM-LPME) was developed and combined with micro-liquid chromatography (micro-LC) for the determination of selected pesticides in water samples. Four pesticides (hexaconazole, procymidone, quinalphos and vinclozolin) were considered as target analytes. Several important extraction parameters such as types of extraction solvent, agitation rate, pH value, total exposure time and effect of salt and humic acids were optimized. Enrichment factors of > 50 folds were easily achieved within 20 min of extraction. The analytical data demonstrated relative standard deviations for the reproducibility of the optimized CSM-LPME method ranging from 6.3 to 7.5%. The correlation coefficients of the calibration curves were at least 0.9995 across a concentration range of 2-100 microg/L. The detection limits for all the analytes were found to be in the range of 1.1-1.9 microg/L.
High temperature liquid chromatography using water-rich and superheated water eluent is evaluated as a new approach for the separation of selected triazole fungicides, hexaconazole, tebuconazole, propiconazole, and difenoconazole. Using a polybutadiene-coated zirconia column at temperatures of 100-150 degrees C, clear separations were achieved when 100% purified water was utilized as organic-free eluent. Excellent limits of detection down to pg level were obtained for the separation of the triazole fungicides under optimum conditions. Van't Hoff plots for the separations were linear suggesting that no changes occurred in the retention mechanism over the temperature range studied.
In this work, a new variation of the electromembrane extraction (EME) approach employing a hollow polymer inclusion membrane (HPIM) was developed. In this method, a HPIM was prepared by casting a solution of the desired proportions of cellulose acetate (CTA), tris(2-ethylhexyl)phosphate (TEHP) and di-(2-ethylhexyl)phosphoric acid (D2EHPA) in dichloromethane on glass capillary tubing. Three basic drugs namely amphetamine, methamphetamine, and 3,4-methylenedioxy-N-methylamphetamine (MDMA) were selected as model analytes to evaluate the extraction performance of this new approach. The drugs were extracted from human plasma samples, through a 20μm thickness HPIM, to an aqueous acceptor solution inside the lumen of the hollow membrane. Parameters affecting the extraction efficiency were investigated in detail. Under the optimized conditions, enrichment factors in the range of 97-103-fold were obtained from 3mL of sample solution with a 10min extraction time and an applied voltage of 300V across the HPIM. The detection limits of the method for the three drugs were in the range of 1.0-2.5ng/mL (at a signal/noise ratio of three), with relative standard deviations of between 6.4% and 7.9%. When the method was applied to spiked plasma samples, the relative recoveries ranged from 99.2% to 100.8%. Enrichment factors of 103, 99 and 97 were obtained for amphetamine, methamphetamine, and MDMA, respectively. A comparison was also made between the newly developed approach and EME using supported liquid membranes (SLM) as well as standard sample preparation methods (liquid-liquid extraction) used by the Toxicology Unit, Department of Chemistry, Malaysia.
Conventional sampling of biological fluids often involves a bulk quantity of samples that are tedious to collect, deliver and process. Miniaturized sampling approaches have emerged as promising tools for sample collection due to numerous advantages such as minute sample size, patient friendliness and ease of shipment. This article reviews the applications and advances of microsampling techniques in therapeutic drug monitoring (TDM), covering the period January 2015 - August 2020. As whole blood is the gold standard sampling matrix for TDM, this article comprehensively highlights the most historical microsampling technique, the dried blood spot (DBS), and its development. Advanced developments of DBS, ranging from various automation DBS, paper spray mass spectrometry (PS-MS), 3D dried blood spheroids and volumetric absorptive paper disc (VAPD) and mini-disc (VAPDmini) are discussed. The volumetric absorptive microsampling (VAMS) approach, which overcomes the hematocrit effect associated with the DBS sample, has been employed in recent TDM. The sample collection and sample preparation details in DBS and VAMS are outlined and summarized. This review also delineates the involvement of other biological fluids (plasma, urine, breast milk and saliva) and their miniaturized dried matrix forms in TDM. Specific features and challenges of each microsampling technique are identified and comparison studies are reviewed.
One of the major drawbacks of electrophoresis in both capillary and microchip is the unsatisfactory sensitivity. Online sample preconcentration techniques can be regarded as the most common and powerful approaches commonly applied to enhance overall detection sensitivity. While the advances of various online preconcentration strategies in capillary and microchip employing aqueous background electrolytes are well-reviewed, there has been limited discussion of the feasible preconcentration techniques specifically developed for capillary and microchip using nonaqueous background electrolytes. This review provides the first consolidated overview of various online preconcentration techniques in nonaqueous capillary and microchip electrophoresis, covering the period of the last two decades. It covers developments in the field of sample stacking, isotachophoresis, and micellar-based stacking. Attention is also given to multi-stacking strategies that have been used for nonaqueous electrophoresis.
An online preconcentration method, namely electrokinetic supercharging (EKS), was evaluated for the determination of tamoxifen and its metabolites in human plasma in nonaqueous capillary electrophoresis with ultraviolet detection (NACE-UV). This method was comprehensively optimized in terms of the leading electrolyte (LE) and terminating electrolyte (TE) injection lengths, as well as electrokinetic sample injection time. The optimized EKS conditions employed were as follows: hydrodynamic injection (HI) of 10mM potassium chloride as LE at 150mbar for 36s (4% of total capillary volume). The sample was injected at 10kV for 300s, followed by HI of 10mM pimozide as TE at 150mbar for 36s (4% of total capillary volume). Separation was performed in 7.5mM deoxycholic acid sodium salt, 15mM acetic acid and 1mM 18-crown-6 in 100% methanol at +25kV with UV detection at 205nm. Under optimized conditions, the sensitivity was enhanced between 160- and 600-fold when compared with our previously developed method based on HI at 150mbar for 12s. The detection limit of the method for tamoxifen and its metabolites were 0.05-0.25ng/mL, with RSDs between 2.1% and 3.5%. Recoveries in spiked human plasma were 95.6%-99.7%. A comparison was also made between the proposed EKS approach and the standard field-amplified sample injection (FASI) technique. EKS proved to be 3-5 times more sensitive than the FASI. The new EKS method was applied to the analysis of tamoxifen and its metabolites in plasma samples from breast cancer patients after liquid-liquid extraction.
A new approach based on the integration of the free liquid membrane (FLM) into electrokinetic supercharging (EKS) was demonstrated to be a new powerful tool used in order to enhance online preconcentration efficiency in capillary electrophoresis (CE). A small plug of water immiscible organic solvent was used as a membrane interface during the electrokinetic sample injection step in EKS in order to significantly enhance the analyte stacking efficiency. The new online preconcentration strategy was evaluated for the determination of paraquat and diquat present in the environmental water samples. The optimised FLM-EKS conditions employed were as follows: hydrodynamic injection (HI) of 20mM potassium chloride as leading electrolyte at 50mbar for 75s (3% of the total capillary volume) followed by the HI of tris(2-ethylhexyl) phosphate (TEHP) as FLM at a 1mm length (0.1% of the capillary volume). The sample was injected at 10kV for 360s, followed by the HI of 20mM cetyl trimethylammonium bromide (CTAB) as terminating electrolyte at 50mbar for 50s (2% of the total capillary volume). The separation was performed in 12mM ammonium acetate and 30mM NaCl containing 20% MeOH at +25kV with UV detection at 205nm. Under optimised conditions, the sensitivity was enhanced between 1500- and 1866-fold when compared with the typical HI at 50mbar for 50s. The detection limit of the method for paraquat and diquat was 0.15-0.20ng/mL, with RSDs below 5.5%. Relative recoveries in spiked river water were in the range of 95.4-97.5%. A comparison was also made between the proposed approach with sole preconcentration of the field-enhanced sample injection (FASI) and EKS in the absence of the FLM.
A new electric-field driven extraction approach based on the integration of a bubbleless electrode into the electromembrane extraction (EME) across hollow polymer inclusion membranes (HPIMs) was demonstrated for the first time. The bubbleless electrode was prepared based on an in-situ synthesised polyacrylamide within a fused silica capillary. The electrode functions as a salt bridge, which conducts the electrical current between the acceptor phase in the lumen of the HPIM and the acceptor solution in the reservoir connected to a high voltage supply through a platinum electrode. Two types of HPIMs were employed, which consisted of desired proportions of cellulose acetate as base polymer, tris(2-ethylhexyl)phosphate as plasticizer, and di-(2-ethylhexyl)phosphoric acid as anionic carrier or Aliquat 336 as cationic carrier, respectively. The EME strategy was evaluated for the simultaneous determination of cationic quaternary ammonium and anionic chlorophenoxy acetic acid herbicides present in the river water, respectively. The analysis was carried out using capillary electrophoresis coupled with UV and contactless conductivity detection. Under the optimised conditions, enrichment factors in the range of 152-185-fold were obtained from 4mL of river water sample with a 20min extraction time and an applied voltage of 3000V. The proposed method provided good linearity with correlation coefficients ranging from 0.9982 to 0.9997 over a concentration range of 1-1000μg/L. The detection limits of the method for the herbicides were in the range of 0.3-0.4μg/L, with relative standard deviations of between 4.8% and 8.5%. The relative recoveries obtained when analysing the spiked river water ranged from 99.1% to 100%. A comparison was also made between the newly developed approach with the conventional EME setup by placing the platinum electrode directly in the lumen of the HPIMs.
A portable microchip electrophoresis (MCE) coupled with on-chip contactless conductivity detection (C(4)D) system was evaluated for the determination of vancomycin in human plasma. In order to enhance the detection sensitivity, a new online multi-stacking preconcentration technique based on field-enhanced sample injection (FESI) and micelle-to-solvent stacking (MSS) was developed and implemented in MCE-C(4)D system equipped with a commercially available double T-junction glass chip. The cationic analytes from the two sample reservoirs were injected under FESI conditions and subsequently focused by MSS within the sample-loading channel. The proposed multi-stacking strategy was verified under a fluorescence microscope using Rhodamine 6G as the model analyte and a sensitivity enhancement factor (SEF) of up to 217 was achieved. The developed approach was subsequently implemented in the aqueous-based MCE, coupled to C(4)D in order to monitor the targeted antibiotic (in this case, vancomycin) present in human plasma samples. The multi-stacking and analysis time for vancomycin were 50s and 250s respectively, with SEF of approximately 83 when compared to typical gated injection. The detection limit of the method for vancomycin was 1.2μg/mL, with intraday and interday repeatability RSDs of 2.6% and 4.3%, respectively. Recoveries in spiked human plasma were 99.0%-99.2%.
A new dispersive inclusion complex microextraction (DICM) approach coupled with ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) for the determination of n-nitrosamine impurities in different medicinal products is demonstrated for the first time. The proposed DICM procedures consist of a dispersive liquid phase microextraction steps employing cyclodextrin as an inclusion complex agent to extract n-nitrosamines namely N-nitrosodimethylamine (NDMA), N-nitrosodiethylamine (NDEA), N-nitrosodiisopropylamine (NDIPA), N-ethyl-N-nitrosoisopropylamine (NEIPA) and N-nitroso-di-n-butylamine (NDBA) present in the medicinal products. The sample solutions were prepared by mixing 5% (m/v) NaCl solution with 1.5 mM β-cyclodextrin and 20 mM sodium dodecyl sulphate to form a stable inclusion complex and subsequently extracted into dichloromethane as an extraction solvent. The enriched solution was reconstituted into aqueous solution prior to UPLC-MS/MS analysis. The method showed good linearity in the range of 0.036-1 ng/mL with a correlation coefficient of at least 0.995, acceptable reproducibility (RSD 0.5-5.8%, n=5), low limits of detection (0.011-0.018 ng/mL), and satisfactory relative recoveries (96-105%). The results obtained were found to be at least 10-fold more sensitive comparable to those obtained using validated direct sample dissolutions coupled with UPLC-MS/MS approach.
Microplastic fibers from textiles have been known to significantly contribute to marine microplastic pollution. However, little is known about the microfiber formation and discharge during textile production. In this study, we have quantified microfiber emissions from one large and representative textile factory during different stages, spanning seven different materials, including cotton, polyester, and blended fabrics, to further guide control strategies. Wet-processing steps released up to 25 times more microfibers than home laundering, with dyeing contributing to 95.0% of the total emissions. Microfiber release could be reduced by using white coloring, a lower dyeing temperature, and a shorter dyeing duration. Thinner, denser yarns increased microfiber pollution, whereas using tightly twisted fibers mitigated release. Globally, wet textile processing potentially produced 6.4 kt of microfibers in 2020, with China, India, and the US as significant contributors. The study underlined the environmental impact of textile production and the need for mitigation strategies, particularly in dyeing processes and fiber choice. In addition, no significant difference was observed between the virgin polyesters and the used ones. Replacing virgin fibers with recycled fibers in polyester fabrics, due to their increasing consumption, might offer another potential solution. The findings highlighted the substantial impact of textile production on microfiber released into the environment, and optimization of material selection, knitting technologies, production processing, and recycled materials could be effective mitigation strategies.
Rapid and direct online preconcentration followed by CE with capacitively coupled contactless conductivity detection (CE-C(4)D) is evaluated as a new approach for the determination of glyphosate, glufosinate (GLUF), and aminophosphonic acid (AMPA) in drinking water. Two online preconcentration techniques, namely large volume sample stacking without polarity switching and field-enhanced sample injection, coupled with CE-C(4)D were successfully developed and optimized. Under optimized conditions, LODs in the range of 0.01-0.1 microM (1.7-11.1 microg/L) and sensitivity enhancements of 48- to 53-fold were achieved with the large volume sample stacking-CE-C(4)D method. By performing the field-enhanced sample injection-CE-C(4)D procedure, excellent LODs down to 0.0005-0.02 microM (0.1-2.2 microg/L) as well as sensitivity enhancements of up to 245- to 1002-fold were obtained. Both techniques showed satisfactory reproducibility with RSDs of peak height of better than 10%. The newly established approaches were successfully applied to the analysis of glyphosate, glufosinate, and aminophosphonic acid in spiked tap drinking water.
Micelle to solvent stacking was implemented for the recently established NACE-C(4) D method to determine tamoxifen and its metabolites in standard samples and human plasma of breast cancer patients. For stacking, the standard samples and extract after liquid-liquid extraction (LLE) were prepared in methanol and the resulting sample solution was pressure injected after a micellar plug of SDS. Factors that affected the stacking such as SDS concentration, micelle, and sample plug length were examined. The sensitivity enhancement factor (peak height from stacking/peak height from typical injection of sample in BGE) was 15-22. The method detection limits with LLE were in the range of 5-10 ng/mL, which was lower than the established method (where the LLE extract was also prepared in methanol) with reported method detection limits of 25-40 ng/mL. The intraday and interday repeatability were in the range of 1.0-3.4% and 3.8-6.5%, respectively.
A new approach for the quantification of tamoxifen and its metabolites 4-hydroxytamoxifen, N-desmethyltamoxifen, and 4-hydroxy-N-desmethyltamoxifen (endoxifen) in human plasma samples using NACE coupled with contactless conductivity detection (C(4) D) is presented. The buffer system employed consisted of 7.5 mM deoxycholic acid sodium salt, 15 mM acetic acid, and 1 mM 18-crown-6 in 100% methanol. The complete separation of all targeted compounds (including endoxifen racemate) could be achieved within 6 min under optimized conditions. The proposed method was validated and showed good linearity in the range from 100 to 5000 ng/mL with correlation coefficients between 0.9922 and 0.9973, LODs in the range of 25-40 ng/mL, and acceptable reproducibility of the peak area (intraday RSD 2.2-3.1%, n = 4; interday (3 days) RSD 6.0-8.8%, n = 4). The developed method was successfully demonstrated for the quantification of tamoxifen and its metabolites in human plasma samples collected from breast cancer patients undertaking tamoxifen treatment.