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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][NTf 2 ] 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.

The translation of stacking techniques used in capillary electrophoresis (CE) to microchip CE (MCE) in order to improve concentration sensitivity is an important area of study. The success in stacking relies on the generation and control of the stacking boundaries which is a challenge in MCE because the manipulation of solutions is not as straightforward as in CE with a single channel. Here, a simple and rapid online sample concentration (stacking strategy) in a battery operated nonaqueous MCE device with a commercially available double T-junction glass chip is presented. A multistacking approach was developed in order to circumvent the issues for stacking in nonaqueous MCE. The cationic analytes from the two loading channels were injected under field-enhanced conditions and were focused by micelle-to-solvent stacking. This was achieved by the application of high electric fields along the two loading channels and a low electric field in the separation channel, with one ground electrode in the reservoir closest to the junction. At the junction, the stacked zones were restacked under field-enhanced conditions and then injected into the separation channels. The multistacking was verified under a fluorescence microscope using Rhodamine 6G as the analyte, revealing a sensitivity enhancement factor (SEF) of 110. The stacking approach was also implemented in the nonaqueous MCE with contactless conductivity detection of the anticancer drug tamoxifen as well as its metabolites. The multistacking and analysis time was 40 and 110 s, respectively, the limit of detections was from 10 to 35 ng/mL and the SEFs were 20 to 50. The method was able to quantify the target analytes from breast cancer patients.

An automated analyte electroextraction and preconcentration system, which was used as the front end for a liquid chromatography-electrospray mass spectrometry instrument, is described. The extraction was based on driving the anionic analytes across a polymer inclusion membrane by application of a potential of 200 V to the cell. Five milliliters (5 mL) of sample were passed through a flow-through cell at a flow rate of 0.2 mL/min containing a membrane 20 μm thick. This consisted of 75% cellulose triacetate as base polymer, 12.5% of tris(2-ethylhexyl)phosphate as plasticizer, and 12.5% of Aliquat 336 as cationic carrier. The target analytes were enriched in 20 μL of a stagnant acceptor solution prior to online LC/MS analysis. The performance of the system was demonstrated for the determination of chlorinated phenoxyacetic acid herbicides in spiked river water. Enrichment factors of ~200 were achieved with recoveries of typically 99% and precision values of typically 5%. The limit of detection (LOD) values were found to be between 0.03 ng/mL to 0.08 ng/mL.

The use of a cationic carrier-mediated polymer inclusion membrane (PIM) for extraction and preconcentration of anionic model analytes driven by an electric field directly into an aqueous acceptor solution is demonstrated. The optimized membrane was 20 μm thick and consisted of 60% cellulose triacetate as base polymer, 20% o-nitrophenyl octyl ether as plasticizer, and 20% Aliquat 336 as cationic carrier in the perchlorate form. By applying voltages of up to 700 V across the membrane, the lipophilic model analytes propanesulfonate, octanesulfonate, and decanesulfonate could be transported from the aqueous donor solution to the aqueous acceptor solution with efficiences >90% within 5 to 20 min. A preconcentration factor of 26, defined by the volume ratio between donor and acceptor compartments of the current cell design, could be achieved. The utility of the method for analytical applications is demonstrated by extraction of the herbicide glyphosate and its breakdown product aminomethylphosphonic acid from spiked river water, followed by quantification with capillary electrophoresis using contactless conductivity detection. Limits of detection of 0.8 and 1.5 ng/mL were obtained for glyphosate and aminomethylphosphonic acid, respectively.