Advanced nanofibrous sorbents for the extraction of pollutants from river water and protein-containing matrices.

The extraction efficiencies of thirty types of fibers produced by meltblown, alternating current electrospinning, and meltblown-co-electrospinning technologies were tested as advanced sorbents for on-line solid-phase extraction in a high-performance liquid chromatography system have been tested and compared with a commercial C18 sorbent. The properties of each fiber, which were often depended on the production process, and their applicability were demonstrated with the extraction of the model analytes nitrophenols and chlorophenols from various matrices including river water and to purify complex matrix human serum and bovine serum albumin from macromolecular ballast. Polycaprolactone fibers outperformed other polymers and were selected for subsequent modifications including (i) incorporation of hybrid carbon nanoparticles, i.e., graphene, activated carbon, and carbon black into the polymer prior to fiber fabrication, and (ii) surface modification by dip coating with polyhydroxy modifiers including graphene oxide, tannin, dopamine, hesperidin, and heparin. These novel fibrous sorbents were comparable to commercial C18 sorbent and provided excellent analyte recoveries of 70-112% even from the protein-containing matrices.

Solvent-assisted dispersive micro-solid phase extraction of bisphenols using iron(III) thenoyltrifluoroacetonate complex (Fe(TTA)3) as a new nanostructured sorbent: a proof of concept.

In this work, we describe for the first time the use of iron(III) thenoyltrifluoroacetonate complex (Fe(TTA)3) as a novel sorbent for solvent-assisted dispersive micro-solid phase extraction (SA-dµSPE) of bisphenols from water samples. The extraction procedure is based on the formation of nanoparticles in situ following the rapid injection of a methanolic solution of Fe(TTA)3 into the stirred aqueous sample. Herein, the synthesis of Fe(TTA)3 and study of the essential parameters of the preparative procedure are described. The optimized procedure allowed for efficient enrichment of bisphenols from various water samples, chosen as model contaminants and matrix, within 2.5 min. The sorbent was collected by centrifugation, dissolved in methanol, and injected to perform HPLC with spectrophotometric detection. The limits of detection and quantification obtained ranged from 1.0-3.1 and 3.1-7.5 µg L-1, respectively. Intraday and interday precisions of <7% relative standard deviation (RSD) and <8% RSD with analyte recoveries ranging between 70-117% (103.8% on average) were obtained for the analysis of river water, wastewater treatment plant effluent, and bottled water.

Lab-in-syringe automated protein precipitation and salting-out homogenous liquid-liquid extraction coupled online to UHPLC-MS/MS for the determination of beta-blockers in serum.

A sample preparation method involving tandem implementation of protein precipitation and salting-out homogenous liquid-liquid extraction was developed for the determination of beta-blockers in serum. The entire procedure was automated using a computer-controlled syringe pump following the Lab-In-Syringe approach. It is based on the denaturation of serum proteins with acetonitrile followed by salt-induced phase separation upon which the proteins accumulate as a compact layer at the interphase of the solutions. The extract is then separated and diluted in-syringe before being submitted to online coupled UHPLC-MS/MS. A 1 mL glass syringe containing a small stir bar for solution mixing at up to 3000 rpm, was used to deal with sample volumes as small as 100 µL. A sample throughput of 7 h-1 was achieved by performing the chromatographic run and sample preparation procedure in parallel. Linear working ranges were obtained for all analytes between 5 and 100 ng mL-1, with LOD values ranging from 0.4 to 1.5 ng mL-1. Accuracy values in the range of 88.2-106% and high precision of <11% RSD suggest applicability for routine analysis that can be further improved using deuterated standards.

Innovated single flush on-line solid-phase extraction in bead injection format for flow programming-based determination of creatinine in human urine.

Reaction-based assays are commonly automated and miniaturized via flow analysis. However, aggressive reagents can affect or destroy even the chemically resistant manifold during long-term use. Using on-line solid-phase extraction (SPE) can eliminate this drawback and allow for high reproducibility and further advanced automation, as presented in this work. Determination of creatinine in human urine, an important clinical marker, by sequential injection analysis was achieved using bead injection on-line SPE with specific UV spectrophotometric detection, providing the necessary sensitivity and selectivity of the method for bioanalysis. The automated SPE column packing and disposal, calibration, and fast measurement highlighted the improvements in our approach. Variable sample volumes and a single working standard solution eliminated matrix effects, broadened the calibration range, and accelerated the quantification. Our method comprised an injection of 20 µL of 100 × times diluted urine with aqueous acetic acid solution pH 2.4, sorption of creatinine in a strong cation exchanger SPE column, washing out urine matrix with 50% aqueous acetonitrile, and elution of creatinine with 1% ammonium hydroxide. The SPE step was accelerated by a single flush of the column when the eluent/matrix wash/sample/standard zones sequence was created in the pump holding coil, and then the sequence of the zones was flushed into the column at once. The whole process was continually spectrophotometrically detected at 235 nm, subtracted from the signal at 270 nm. A single run duration was less than 3.5 min. Method relative standard deviation was <5.0% (n = 6). A calibration range was linear within the range of 0.02-0.30 µg creatinine (R > 0.999), covering 1.0-15.0 mmol/L creatinine in urine. The standard addition method used two different volumes of a single working standard solution for quantification. Results proved the effectiveness of our improvements in the flow manifold, bead injection, and automated quantification. The accuracy of our method was comparable to the routine enzymatic assay of real urine samples in a clinical laboratory.

Comparing adsorption performance of microfibers and nanofibers with commercial molecularly imprinted polymers and restricted access media for extraction of bisphenols from milk coupled with liquid chromatography.

Advanced solid phase extraction (SPE) fibrous sorbents including polyethylene, polypropylene poly (hydroxybutyrate), and polyamide 6 nanofibers, polycaprolactone microfibers/nanofibers, polycaprolactone microfibers/polyvinylidene difluoride nanofibers, and poly (hydroxybutyrate) microfibers/polypropylene microfibers composites, as well as commercial molecularly imprinted polymers and restricted access media sorbent were compared in terms of bisphenols extraction from milk and their clean-up efficiency. Three on-line SPE-HPLC methods were completely validated for the extraction and detection of bisphenols A, AF, C, A diglycidyl ether, and F diglycidyl ether in bovine milk. Polycaprolactone composite nanofibers compared favorably to restricted access media, enabled excellent clean-up of bisphenols from the proteinaceous matrix, and yielded recoveries 98.0-124.5% and 93.0-115.0%, respectively, with RSD less than 10%. Total analysis time including on-line SPE step lasted only 12 min, which represents a significant reduction in time compared with previously reported as well as official European Union and AOAC methods defined for the determination of bisphenols in various matrices.

Automated centrifugation-less milk deproteinization and homogenous liquid-liquid extraction of sulfonamides for online liquid chromatography.

A novel approach to the determination of sulfonamides in milk based on the Lab-In-Syringe technique is presented. The method involves automated salting-out liquid-liquid extraction of the analytes, allowing simultaneous sample deproteination without requiring centrifugation or manual sample handling. The procedural parameters, including salt type, solvent-to-sample ratio, and salt solution volume, were studied. The extracts obtained were diluted in situ and transferred to online coupled liquid chromatography for analyte separation carried out in parallel to the subsequent extraction. In this way, a sample throughput of approximately 6 h-1 was achieved. The detection limits ranged from 25 to 32 µg L-1 using a 500 µL milk sample and spectrophotometric detection. The applicability of the developed method to sample analysis was proven by recovery values ranging from 73.2% to 94.1% (86.3% on average) for milk samples of different fat content spiked at 3 µg mL-1 level. Straightforward automation of one of the most laborious preparation steps in food analysis, i.e., deproteination, was demonstrated.

A simple method to quantify azo dyes in spices based on flow injection chromatography combined with chemometric tools.

Para Red (PR) and Sudan dyes have been illegally used as colorants to adulterate certain foods by enhancing their red/orange colour. In addition, they are toxic and carcinogenic. This work presents the development of a simple flow injection chromatographic method combined with chemometric tools to perform the determination of PR, Sudan I (SI) and Sudan II (SII) in food samples. The flow chromatographic system consisted of a low-pressure manifold coupled to a reverse phase monolithic column. A Partial Least Square (PLS) model was applied to resolve overlapped absorption spectra registered for each dye at the corresponding retention time. The relative errors of calibration (RMSECV, %) were 0.49, 0.85 and 0.23, and the relative errors of prediction (RMSEP, %) were 1.12, 0.75 and 0.33 for PR, SI and SII, respectively. The residual predictive deviation (RPD) values obtained were higher than 3.00 for all analytes. The method was successfully applied to quantify the dyes in six different commercial spices samples. The results were compared with the HPLC reference method concluding that there were no significant differences at the studied confidence level (α = 0.05). The proposed method can be used to rapidly determine the analytes in a simple, reliable, low-cost and environmentally-friendly manner. Supplementary Information: The online version contains supplementary material available at 10.1007/s13197-021-05299-8.

Renewable sorbent dispersive solid phase extraction automated by Lab-In-Syringe using magnetite-functionalized hydrophilic-lipophilic balanced sorbent coupled online to HPLC for determination of surface water contaminants.

An automated methodology for magnetic dispersive solid phase microextraction integrating bead injection approach for renewable sorbent introduction is presented for the first time and was successfully applied to the enrichment of water contaminants. For this purpose, a simple procedure was developed for the functionalization of commercial SupelTM-Select HLB (Hydrophilic modified styrene polymer) sorbent beads that allowed embedding magnetite nanoparticles (Fe3O4). The sorbent was then used in a dispersive solid phase extraction procedure that was carried out entirely inside the void of an automatic syringe pump following the flow-batch concept of Lab-In-Syringe including automated renewal of the sorbent for each analysis. Mixing processes, sorbent dispersion, and sorbent recovery were enabled by using a strong magnetic stirring bar, fabricated from a 3D printed polypropylene casing and neodymium magnets, inside the syringe. The final extract was submitted to online coupled liquid chromatography with spectrometric detection. System and methodology were applied to determine mebendazole, bisphenol A, benzyl 4-hydroxybenzoate, diclofenac, and triclosan selected as models from different groups of environmental contaminants of current concern. Experimental parameters including extraction and elution times, composition and volume of eluent, and bead recollection were optimized. Required system elements were produced by 3D printing. Enlarging the sample volume by repeated extraction to enhance the sensitivity of the method was studied. Using double extraction from 3.5 mL, limits of detection ranged from 1.2 µg L-1 to 6.5 µg L-1 with an RSD (n = 6) value less than 7% for all the analytes at 25 µg L-1 level. The method was linear in the range of 5-200 µg L-1 and was successfully implemented for the analysis of surface waters with analyte recoveries ranging from 78.4% to 105.6%.

Lab-In-Syringe automation of deep eutectic solvent-based direct immersion single drop microextraction coupled online to high-performance liquid chromatography for the determination of fluoroquinolones.

Lab-In-Syringe direct immersion single drop microextraction is proposed as an automated sample pretreatment methodology and coupled online to HPLC with fluorescence detection for the determination of fluoroquinolones in environmental waters. For the first time, a drop of a natural deep eutectic solvent (NADES), synthesized from hexanoic acid and thymol, has been used as an extractant in automated single-drop microextraction. The extraction procedure was carried out within the 5 mL void of an automatic syringe pump. A 9-position head valve served the aspiration of all required solutions, air, waste disposal, and hyphenation with the HPLC instrument. Sample mixing during extraction was done by a magnetic stirring bar placed inside the syringe. Only 60 µL of NADES were required omitting toxic classical solvents and improving the greenness of the proposed methodology. By direct injection, linear working ranges between 0.1 and 5 µg L-1 were achieved for all fluoroquinolones. The limit of quantification values and enrichment factors ranged from 20 ng L-1 to 30 ng L-1 and 35 to 45, respectively. Accuracies obtained from the analysis of spiked surface water and wastewater treatment plant effluent analysis at two concentration levels (0.5 and 4 µg L-1) ranged from 84.6% to 119.7%, with RSD values typically <3%.

Lab-In-Syringe with Bead Injection Coupled Online to High-Performance Liquid Chromatography as Versatile Tool for Determination of Nonsteroidal Anti-Inflammatory Drugs in Surface Waters.

We report on the hyphenation of the modern flow techniques Lab-In-Syringe and Lab-On-Valve for automated sample preparation coupled online with high-performance liquid chromatography. Adopting the bead injection concept on the Lab-On-Valve platform, the on-demand, renewable, solid-phase extraction of five nonsteroidal anti-inflammatory drugs, namely ketoprofen, naproxen, flurbiprofen, diclofenac, and ibuprofen, was carried out as a proof-of-concept. In-syringe mixing of the sample with buffer and standards allowed straightforward pre-load sample modification for the preconcentration of large sample volumes. Packing of ca. 4.4 mg microSPE columns from Oasis HLB® sorbent slurry was performed for each sample analysis using a simple microcolumn adapted to the Lab-On-Valve manifold to achieve low backpressure during loading. Eluted analytes were injected into online coupled HPLC with subsequent separation on a Symmetry C18 column in isocratic mode. The optimized method was highly reproducible, with RSD values of 3.2% to 7.6% on 20 µg L-1 level. Linearity was confirmed up to 200 µg L-1 and LOD values were between 0.06 and 1.98 µg L-1. Recovery factors between 91 and 109% were obtained in the analysis of spiked surface water samples.

Sequential Injection Analysis for Automation and Evaluation of Drug Liberation Profiles: Clotrimazole Liberation Monitoring.

A fully automated sequential injection system was tested in terms of its application in liberation testing, and capabilities and limitations were discussed for clotrimazole liberation from three semisolid formulations. An evaluation based on kinetic profiles obtained in short and longer sampling intervals and steady-state flux values were applied as traditional methods. The obtained clotrimazole liberation profile was faster in the case of Delcore and slower for Clotrimazol AL and Canesten cream commercial formulations. The steady-state flux values for the tested formulations were 52 µg cm-2 h-1 for Canesten, 35 µg cm-2 h-1 for Clotrimazol AL, and 7.2 µg cm-2 h-1 for Delcore measured in 4 min sampling intervals. A simplified approach for the evaluation of the initial rate based on the gradient between the second and third sampling points was used for the first time and was found to correspond well with the results of the conventional methods. A comparison based on the ratio of the steady-state flux and the initial rate values for Canesten and Clotrimazol AL proved the similarity of the obtained results. The proposed alternative was successfully implemented for the comparison of short-term kinetic profiles. Consequently, a faster and simpler approach for dissolution/liberation testing can be used.

Inhibition of AKR1B10-mediated metabolism of daunorubicin as a novel off-target effect for the Bcr-Abl tyrosine kinase inhibitor dasatinib.

Bcr-Abl tyrosine kinase inhibitors significantly improved Philadelphia chromosome-positive leukaemia therapy. Apart from Bcr-Abl kinase, imatinib, dasatinib, nilotinib, bosutinib and ponatinib are known to have additional off-target effects that might contribute to their antitumoural activities. In our study, we identified aldo-keto reductase 1B10 (AKR1B10) as a novel target for dasatinib. The enzyme AKR1B10 is upregulated in several cancers and influences the metabolism of chemotherapy drugs, including anthracyclines. AKR1B10 reduces anthracyclines to alcohol metabolites that show less antineoplastic properties and tend to accumulate in cardiac tissue. In our experiments, clinically achievable concentrations of dasatinib selectively inhibited AKR1B10 both in experiments with recombinant enzyme (Ki = 0.6 µM) and in a cellular model (IC50 = 0.5 µM). Subsequently, the ability of dasatinib to attenuate AKR1B10-mediated daunorubicin (Daun) resistance was determined in AKR1B10-overexpressing cells. We have demonstrated that dasatinib can synergize with Daun in human cancer cells and enhance its therapeutic effectiveness. Taken together, our results provide new information on how dasatinib may act beyond targeting Bcr-Abl kinase, which may help to design new chemotherapy regimens, including those with anthracyclines.

The role of pKa, log P of analytes, and protein matrix in solid-phase extraction using native and coated nanofibrous and microfibrous polymers prepared via meltblowing and combined meltblowing/electrospinning technologies.

Effect of physicochemical properties including dissociation constant (pKa) and partition coefficient (log P) of the compounds on their extraction efficiency in sample preparation using fibrous polymer sorbents has been demonstrated. Poly-ε-caprolactone as meltblown/electrospun composite fibers, and polypropylene, polyethylene, poly(3-hydroxybutyrate), poly(lactic acid), and polyamide 6 in the meltblown fiber format were used as sorbents in solid-phase extraction. In addition, the polycaprolactone fibers were coated with dopamine, dopamine combined with heparin, and tannin, respectively, to modify their extraction properties. These fibers that were not yet used for extractions and the unique combination of sorbents and analytes significantly extends the scope of nanofibrous extraction. The extraction efficiency was determined using model pharmaceuticals including acetylsalicylic acid, moxonidine, metoprolol, propranolol, propafenone, diltiazem, atorvastatin, and amiodarone. These model compounds displayed the widest differences in both pKa and log P values. The extraction efficiency of some of the fibers reached 96.64%. Coating of polycaprolactone fibers with dopamine significantly improved extraction efficiency of slightly retained metoprolol while moxonidine was not retained on any sorbent. The fibrous sorbents were also tested for extraction of pharmaceuticals in bovine serum albumin and human serum, respectively, to demonstrate their capability to extract them from a complex protein-containing matrix. The clean-up efficiency of our fibers was compared with that of a commercial restricted access media (RAM) C-18 alkyl-diol silica column. Our technique is in accordance with the requirements of modern sample preparation techniques.

3D printed permeation module to monitor interaction of cell membrane transporters with exogenic compounds in real-time.

A new design of permeation module based on 3D printing was developed to monitor the interaction of exogenic compounds with cell membrane transporters in real-time. The fluorescent marker Rhodamine 123 (Rho123) was applied as a substrate to study the activity of the P-glycoprotein membrane transporter using the MDCKII-MDR1 genetically modified cell line. In addition, the inhibitory effect of verapamil (Ver), a prototype P-glycoprotein inhibitor, was examined in the module, demonstrating an enhanced Rho123 transfer and accumulation into cells as well as the applicability of the module for P-glycoprotein inhibitor testing. Inhibition was demonstrated for different ratios of Rho123 and Ver, and their competition in terms of interaction with the P-glycoprotein transporter was monitored in real-time. Employing the 3D-printed module, permeation testing was shortened from 8 h in the conventional module to 2 h and evaluation based on kinetic profiles in every 10 min was possible in both donor and acceptor compartments. We also show that monitoring Rho123 levels in both compartments enables calculate the amount of Rho123 accumulated inside cells without the need of cell lysis.

Lab-In-Syringe for automated double-stage sample preparation by coupling salting out liquid-liquid extraction with online solid-phase extraction and liquid chromatographic separation for sulfonamide antibiotics from urine.

A double-stage Lab-In-Syringe automated extraction procedure coupled online to HPLC for the determination of four sulfonamides in urine has been developed. Our method is based on homogeneous liquid-liquid extraction at pH 3 using water-miscible acetonitrile with induction of phase separation by the addition of a saturated solution of kosmotropic salts MgSO4 and NaCl. The procedure allowed extraction of the moderately polar model analytes and the use of a solvent that is compatible with the used separation technique. The automated sample preparation system based on the stirring-assisted Lab-In-Syringe approach was coupled on-line with HPLC-UV for the subsequent separation of the sulfonamide antibiotics. To improve both preconcentration factor and extract cleanup, the analytes were trapped at pH 10 in an anion-exchange resin cartridge integrated into the HPLC injection loop thus achieving a double-stage sample clean-up. Analytes were eluted using an acidic HPLC mobile phase in gradient elution mode. Running the analytes separation and the two-step preparation of the following sample in parallel reduced the total time of analysis to mere 13.5 min. Limits of detection ranged from 5.0 to 7.5 µg/L with linear working ranges of 50-5000 µg/L (r2 > 0.9997) and RSD ≤ 5% (n = 6) at a concentration level of 50 µg/L. Average recovery values were 102.7 ± 7.4% after spiking of urine with sulfonamides at concentrations of 2.5 and 5 mg/L followed by 5 times dilution. To the best of our knowledge, the use of Lab-In-Syringe for the automation of coupled homogeneous liquid-liquid extraction and SPE for preparation of the complex matrices suitable for separation techniques is here presented for the first time.

Determination of Ochratoxin A and Ochratoxin B in Archived Tokaj Wines (Vintage 1959-2017) Using On-Line Solid Phase Extraction Coupled to Liquid Chromatography.

According to the EU legislation, ochratoxin A contamination is controlled in wines. Tokaj wine is a special type of sweet wine produced from botrytized grapes infected by "noble rot" Botrytis cinerea. Although a high contamination was reported in sweet wines and noble rot grapes could be susceptible to coinfection with other fungi, including ochratoxigenic species, no screening of Tokaj wines for mycotoxin contamination has been carried out so far. Therefore, we developed an analytical method for the determination of ochratoxin A (OTA) and ochratoxin B (OTB) involving online SPE coupled to HPLC-FD using column switching to achieve the fast and sensitive control of mycotoxin contamination. The method was validated with recoveries ranging from 91.6% to 99.1% with an RSD less than 2%. The limits of quantification were 0.1 and 0.2 µg L-1 for OTA and OTB, respectively. The total analysis time of the online SPE-HPLC-FD method was a mere 6 min. This high throughput enables routine analysis. Finally, we carried out an extensive investigation of the ochratoxin contamination in 59 Slovak Tokaj wines of 1959-2017 vintage. Only a few positives were detected. The OTA content in most of the checked wines did not exceed the EU maximum tolerable limit of 2 µg L-1, indicating a good quality of winegrowing and storing.

On-line polydopamine coating as a new way to functionalize polypropylene fiber sorbent for solid phase extraction.

Effective process, including a cartridge packing polypropylene fiber sorbent modified by following on-line polydopamine coating, for on-line solid phase extraction in 2D UHPLC system has been developed. Hydrophobic surface of mechanically stable polypropylene fibers was hydrophilized using an automated and reproducible in situ coating process to enable good wettability and effective extraction of polar compounds. Polymerization mixture consisting dopamine and TRIS buffer was circulated through the cartridge containing polypropylene fibers using a peristaltic pump to achieve polymerization. This process was optimized in terms of dopamine amount in the polymerization mixture, its flow rate, and polymerization time. Best results were obtained with 25 mL polymerization mixture containing 20 mg dopamine circulated through the cartridge at a flow rate of 2.07 mL min-1 for 60 min. Prepared cartridges were evaluated via measurement of the recovery and reproducibility using chlorogenic acid as a model compound. Overall reproducibility of our multistep process including eight cartridges in 2D UHPLC system, each measured in triplicate, was 3.61% (n = 24).

Doping Polysulfone Membrane with Alpha-Tocopherol and Alpha-Lipoic Acid for Suppressing Oxidative Stress Induced by Hemodialysis Treatment.

The reduction of free radicals by bioactive membranes used for hemodialysis treatment is an important topic due to the constant rise of oxidative stress-associated cardiovascular mortality by hemodialysis patients. Therefore, it is urgent to find an effective solution that helps to solve this problem. Polysulfone membranes enriched with α-lipoic acid, α-tocopherol, and with both components are fabricated by spin coating. The antioxidant properties of these membranes are evaluated in vitro by determining the lipid-peroxidation level and the total antioxidant status of the blood plasma. The biocompatibility is assessed by quantifying the protein adsorption, platelet adhesion, complement activation, and hemolytic effect. All types of membranes show in vitro antioxidant activity and a trend to reduce oxidative stress in vivo; the best results show membranes prepared with a combination of both compounds and prove to be nonhemolytic and hemocompatible. Moreover, the membrane specific separation ability for the main waste products is not affected by antioxidants incorporation.

Nanofibers as advanced sorbents for on-line solid phase extraction in liquid chromatography: A tutorial.

Polymers in nanofiber format promise a great potential as sorbents for extraction techniques. This tutorial provides an overview of direct coupling of extraction techniques based on nanofibers to liquid chromatography. Arrangements of the fibers in conventional extraction cartridges are demonstrated. Selection of suitable nanomaterials according to their surface density, wettability, and mechanical stability is proposed and personal experience of the authors commented. Optimization of on-line extraction procedure, practical aspects, technical problems, pitfalls, pros, and cons of using nanofibers for extraction in high-pressure chromatography systems are also discussed and several examples presented. The following text comprehensively summarizes numerous reports that dealt with the topic. Future perspectives of advanced nanofiber materials and approaches that concern polymer fibers modifications are also included.

Poly-ε-caprolactone Nanofibrous Polymers: A Simple Alternative to Restricted Access Media for Extraction of Small Molecules from Biological Matrixes.

Poly-ε-caprolactone nanofibrous polymer has been used as an alternative to restricted access media for extraction of protein-containing biological samples and direct transfer in the chromatographic system. Three commercial cartridges differing in length and internal diameter have been manually packed with the composite material prepared from poly-ε-caprolactone nanofibers coated on poly-ε-caprolactone microfibrous scaffold and connected to the column-switching chromatographic system. Bovine milk and human serum (25 µL) spiked with a mixture of methyl-, ethyl-, propyl-, and butylparaben in a concentration range of 1-100 µg mL-1 were online extracted using the cartridge-containing fibers. Then, 5 and 20% (v/v) aqueous methanol was applied as the washing mobile phase. While the ballast protein macromolecules were quantitatively eluted from the nano/microfibrous composite sorbent, the parabens were retained. After the mobile phase was switched to a stronger one, these compounds were then eluted from the extraction sorbent, directed in the analytical column, and finally separated. An extraction efficiency of 86-101% for all parabens achieved using the optimum-sized cartridge and a repeatability of the extraction procedure of 0.06-1.95% RSD were obtained.