Dialysis of one sample drop on-line connected with electrophoresis in short capillary

A new coaxial flow-through probe for electromembrane extraction of methadone from clinical samples on-line coupled to capillary electrophoresis

BACKGROUND

A new design of a flow-through coaxial electromembrane extraction (EME) probe that can be on-line coupled with CE instrument is described and tested. The supporting base of the probe is a PDMS microchip with T-shaped channels into which two coaxially arranged capillaries for inlet and outlet solutions are inserted. The extraction part of the probe is a porous polypropylene hollow fiber, sealed at one end and modified with nitrophenyloctyl ether (NPOE) extraction fluid. The internal volume of the extraction probe is 1.1 μL.

RESULTS

The EME probe was tested on laboratory samples and methadone was extracted into 3.0 M AcOH as acceptor. The concentration dependence was linear in the range of 0.1-1.0 μg mL-1 at EME 300 s/150 V and in the range of 0.5-10.0 μg mL-1 at EME 100 s/150 V. The enrichment factor was greater than 30 and the LOD was 0.21 μg mL-1. The EME of methadone in clinical samples showed a linear concentration dependence in human urine and a nonlinear concentration dependence in serum. The distribution of methadone in each phase of the extraction system and the effect of extraction membrane thickness on the enrichment factor were studied. The EME probe can be applied repeatedly.

SIGNIFICANCE

The supporting base of EME probe and flow gating interface (FGI) are realized by a microfluidic PDMS microchips cast in the laboratory without the use of lithography. A supporting PDMS chip with coaxially arranged capillaries and extraction membrane forms a compact analytical instrument. The entire EME/CE analysis process is performed on a laboratory-made instrument and automated by LabView.

Progress in on-line, at-line, and in-line coupling of sample treatment with capillary and microchip electrophoresis over the past 10 years: A review

The review presents an evaluation of the development of on-line, at-line and in-line sample treatment coupled with capillary and microchip electrophoresis over the last 10 years. In the first part, it describes different types of flow-gating interfaces (FGI) such as cross-FGI, coaxial-FGI, sheet-flow-FGI, and air-assisted-FGI and their fabrication using molding into polydimethylsiloxane and commercially available fittings. The second part deals with the coupling of capillary and microchip electrophoresis with microdialysis, solid-phase, liquid-phase, and membrane based extraction techniques. It mainly focuses on modern techniques such as extraction across supported liquid membrane, electroextraction, single drop microextraction, head space microextraction, and microdialysis with high spatial and temporal resolution. Finally, the design of sequential electrophoretic analysers and fabrication of SPE microcartridges with monolithic and molecularly imprinted polymeric sorbents are discussed. Applications include the monitoring of metabolites, neurotransmitters, peptides and proteins in body fluids and tissues to study processes in living organisms, as well as the monitoring of nutrients, minerals and waste compounds in food, natural and wastewater.

A new electromembrane extraction probe for on-line connection with capillary electrophoresis for determination of substances in biological matrices

A miniature probe for electromembrane extraction is developed and constructed. The tubular probe with an internal volume of 1.1 μL is made of polypropylene hollow fiber with a supported liquid membrane of 85% nitrophenyloctyl ether (NPOE) with 15% bis(2-ethylhexyl)phosphonic acid (DEHP). The probe is connected on-line to the electrophoresis with short separation capillary via an air assisted flow gating interface cast from poly (dimethylsiloxane). The compact instrument is computer controlled via LabView. The probe parameters are tested for extraction of creatinine and basic amino acids from artificial solution and human urine. The sensitivity of the electrophoretic determination after 300 s extraction at 150 V compared to the sensitivity without extraction is 4.9-fold and 2.6-fold higher for creatinine and arginine, respectively. The RSDs for peak area measured from 5 repeated extractions of 50 μM solutions are 7.5%, 7.2%, 8.6% and 9.2% for Crea, Lys, Arg and His, respectively. The probe can be used for all-day measurements. The preparation of the probe is simple and requires no special tool.

Microdialysis as a tool for antibiotic assessment in patients with diabetic foot: a review

Diabetic foot is a serious late complication frequently caused by infection and ischaemia. Both require prompt and aggressive treatment to avoid lower limb amputation. The effectiveness of peripheral arterial disease therapy can be easily verified using triplex ultrasound, ankle-brachial/toe-brachial index examination, or transcutaneous oxygen pressure. However, the success of infection treatment is difficult to establish in patients with diabetic foot. Intravenous systemic antibiotics are recommended for the treatment of infectious complications in patients with moderate or serious stages of infection. Antibiotic therapy should be initiated promptly and aggressively to achieve sufficient serum and peripheral antibiotic concentrations. Antibiotic serum levels are easily evaluated by pharmacokinetic assessment. However, antibiotic concentrations in peripheral tissues, especially in diabetic foot, are not routinely detectable. This review describes microdialysis techniques that have shown promise in determining antibiotic levels in the surroundings of diabetic foot lesions.

Amino acids in inflammatory bowel diseases: Modern diagnostic tools and methodologies

Amino acids are crucial building blocks of living organisms. Together with their derivatives, they participate in many intracellular processes to act as hormones, neuromodulators, and neurotransmitters. For several decades amino acids have been studied for their potential as markers of various diseases, including inflammatory bowel diseases. Subsequent improvements in sample pretreatment, separation, and detection methods have enabled the specific and very sensitive determination of these molecules in multicomponent matrices-biological fluids and tissues. The information obtained from targeted amino acid analysis (biomarker-based analytical strategy) can be further used for early diagnostics, to monitor the course of the disease or compliance of the patients. This review will provide an insight into current knowledge about inflammatory bowel diseases, the role of proteinogenic amino acids in intestinal inflammation and modern analytical techniques used in its diagnosis and disease activity monitoring. Current advances in the analysis of amino acids focused on sample pretreatment, separation strategy, or detection methods are highlighted, and their potential in clinical laboratories is discussed. In addition, the latest clinical data obtained from the metabolomic profiling of patients suffering from inflammatory bowel diseases are summarized with a focus on proteinogenic amino acids.

Characterization of various geometric arrangements of "air-assisted" flow gating interfaces for capillary electrophoresis

For connecting flow-through analytical methods with capillary electrophoresis, a chip working in the air-assisted flow gating interface regime is cast from poly(dimethylsiloxane). In the injection space, the exit from the delivery capillary is placed close to the entrance to the separation capillary. Prior to injecting the sample into the separation capillary, the background electrolyte is forced out of the injection space by a stream of air. In the empty space, a drop of the sample with a volume of <100 nL is formed between the exit from the delivery capillary and the entrance into the separation capillary, from which the sample is injected hydrodynamically into the separation capillary. After injection, the injection space is filled with BGE, and the separation can be begun. Three geometric variants for the mutual geometric arrangement of the delivery and separation capillaries were tested: the delivery capillary is placed perpendicular to the separation capillary, from either above or below, or the capillaries are placed axially, that is, directly opposite one another. All of the variants are equivalent from the analytical and separation efficiency viewpoints. The repeatability expressed by RSD is up to 5%. The tested flow gating interface variants are also suitable for continuous and discontinuous sampling at flow rates of the order of units of μL/min. The developed instrument for sequential electrophoretic analysis operates fully automatically and is suitable for rapid sequential monitoring of dynamic processes.

Determination of amino acids by capillary and microchip electrophoresis with contactless conductivity detection - Theory, instrumentation and applications

This review article summarises aspects of the determination of amino acids using capillary and chip electrophoresis in combination with contactless conductivity detection from their historical beginnings to the present time. Discussion is included of the theory of conductivity detection in electromigration techniques, the design of contactless conductivity cells for detection in capillaries and on microchips, including the use of computer programs for simulation of the conductivity response and the process of the electrophoretic separation of amino acids. Emphasis is placed on optimisation of the background electrolyte composition, chiral separation, multidimensional separation, stacking techniques and the use of multidetection systems. There is also a description of clinical applications, the determination of amino acids in foodstuffs, waters, soils and composts with emphasis on modern techniques of sample treatment, such as microdialysis, liquid membrane extraction and many other techniques.

Droplet-interfacing strategies in microscale electrophoresis for sample treatment, separation and quantification: A review

In this study, for the first time we report on a comprehensive overview of different strategies to hyphenate droplet-based sample handling and preparation with electrophoretic separation in different formats (i.e. microchip and capillary electrophoresis). Droplet-interfaced electrophoresis is an emerging technique in which micro/nanometric droplets are used as a bridge and carrier of target analytes between sample treatment and electrokinetic separation steps, thus being expected to overcome the challenges of working dimension mismatch and low degree of module integration. This review covers all works on this topic from 2006 (the year of the first communication) up to 2020, with focus being given to three principal interfacing strategies, including droplets in immiscible phases, digital microfluidics with electrowetting-on-dielectric principle and inkjet droplet generation. Different instrumental developments for such purpose, the viewpoints on pros and cons of these designs as well as application demonstrations of droplet-interfaced electrokinetic strategies are discussed.