Electrophoretic analysis of cations using large-volume sample stacking with an electroosmotic flow pump using capillaries coated with neutral and cationic polymers

On-line sample preconcentration by LVSEP-FASI with simple voltage control on Y-channel chips

To eliminate complicated voltage controls for highly sensitive microchip electrophoresis (MCE) analyses on the basis of combining two online sample preconcentration techniques, large-volume sample stacking with an electroosmotic flow (EOF) pump (LVSEP) and field-amplified sample injection (FASI), cross-channel microchips and a multichannel high-voltage power supply were replaced to Y-channel chips and a conventional power supply designed for capillary electrophoresis, respectively. By simple switching of the electric circuit after the LVSEP-FASI sample enrichments, the focused analytes could be separated during anodic migration in a separation channel. In the LVSEP-FASI analysis of fluorescein using the Y-channel microchip, the maximum sensitivity enhancement factor (SEF) of 7400 was achieved, resulting in a 30-fold detectability increase compared to the conventional LVSEP. The developed method was applied to the oligosaccharide analysis in MCE. As a result, the SEF for maltotriose was improved from 450 to 2300 and the baseline separation of the oligosaccharides was achieved without any complicated voltage control in LVSEP-FASI on the Y-channel chips.

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.

Large volume sample stacking of antiepileptic drugs in counter current electrophoresis performed in PAMAPTAC coated capillary

Electrophoretic stacking is developed for sensitive determination of three zwitterionic antiepileptics, namely vigabatrin, pregabalin and gabapentin, in human serum. CE separation is performed in a 25 μm fused silica capillary covalently coated with the copolymer of acrylamide with 5% content of permanently charged 3-acrylamidopropyl trimethylammonium chloride (PAMAPTAC). In background electrolyte of 500 mM acetic acid, the 5% PAMAPTAC generates an anodic electro-osmotic flow with a magnitude of (-18.6 ± 0.5) · 10^-9 m²V^-1s^-1, which acts against the direction of the electrophoretic migration of the analytes. A sample of the antiepileptic prepared in a 25% v/v infusion solution and 75% v/v acetonitrile is injected into the capillary in a large volume attaining a zone length of up to 270 mm. After turning on the separation voltage, the antiepileptics are isotachophoretically focussed behind the zone of Na⁺ ions with a sensitivity enhancement factor of 78. For the clinical determination of antiepileptics, the human serum is diluted with acetonitrile in a ratio of 1:3 v/v and a zone with a length of 90 mm is injected into the capillary. The method is linear in the 0.025-2.5 μg/mL concentration range; the attained limit of quantification is in the range 18.3-22.8 nmol/L; the within-day precision for the migration time is 0.8-1.2% and for the peak area 1.5-2.4%.

Advancement of electroosmotic pump in microflow analysis: A review

This review (with 152 references) covers the progress made in the development and application of electroosmotic pumps in a period from 2009 through 2018 in microflow analysis. Following a short introduction, the review first categorizes various electroosmotic pumps into five subclasses based on the materials used for pumping: i) open channel EOP, 2) packed-column EOP, iii) porous monolith EOP, iv) porous membrane EOP, and v) other types of EOP. Pumps in each subclass are discussed. A next section covers EOP applications, primarily the applications of EOPs in micro flow analysis and micro/nano liquid chromatography. Other scattered applications are also examined. Perspectives, trends and challenges are discussed in the final section.

Sample Preconcentration Protocols in Microfluidic Electrophoresis

Electrophoretic on-line sample preconcentration techniques in microfluidic channels improve the sensitivity prior to the separation. Among various techniques, the most important field-amplified sample stacking and sweeping on cross-channel microchips are demonstrated. As a novel microfluidic preconcentration approach, a large-volume sample stacking with electroosmotic flow pump (LVSEP) on straight-channel chips is also presented, which can omit a complicated voltage program for sample injection processes. In this chapter, we describe how to prepare and how to run these on-line sample preconcentration methods in microchip electrophoresis.

Recent trends in capillary electrophoresis for complex samples analysis: A review

CE has been a continuously evolving analytical methodology since its first introduction in the 1980s of the last century. The development of new CE separation procedures, the coupling of these systems to more sensitive and versatile detection systems, and the advances in miniaturization technology have allowed the application of CE to the resolution of new and complex analytical problems, overcoming the traditional disadvantages associated with this method. In the present work, different recent trends in CE and their application to the determination of high complexity samples (as biological fluids, individual cells, etc.) will be reviewed: capillary modification by different types of coatings, microfluidic CE, and online microextraction CE. The main advantages and disadvantages of the different proposed approaches will be discussed with examples of most recent applications.

Analysis of endogenous nucleotides by single cell capillary electrophoresis-mass spectrometry

Analytical technologies that enable investigations at the single cell level facilitate a range of studies; here a lab-fabricated capillary electrophoresis-electrospray ionization-mass spectrometry (CE-ESI-MS) platform was used to analyze anionic metabolites from individual Aplysia californica neurons. The system employs a customized coaxial sheath-flow nanospray interface connected to a separation capillary, with the sheath liquid and separation buffer optimized to ensure a stable spray. The method provided good repeatability of separation and reliable detection sensitivity for 16 mono-, di- and triphosphate nucleosides. For a range of anionic analytes, including cyclic adenosine monophosphate (cAMP), adenosine diphosphate (ADP) and adenosine triphosphate (ATP), the detection limits were in the low nanomolar range (<22 nM). A large Aplysia R2 neuron was used to demonstrate the ability of CE-ESI-MS to quantitatively characterize anionic metabolites within individual cells, with 15 nucleotides and derivatives detected. Following the method validation process, we probed smaller, 60 μm diameter Aplysia sensory neurons where sample stacking was used as a simple on-line analyte preconcentration approach. The calculated energy balance ([ATP] + 0.5 × [ADP])/([AMP] + [ADP] + [ATP]) of these cells was comparable with the value obtained from bulk samples.

Toward 10,000-fold sensitivity improvement of oligosaccharides in capillary electrophoresis using large-volume sample stacking with an electroosmotic flow pump combined with field-amplified sample injection

A combination of two online sample concentration techniques, large-volume sample stacking with an electroosmotic flow pump (LVSEP) and field-amplified sample injection (FASI), was investigated in CE to achieve highly sensitive oligosaccharide analysis. In CE with LVSEP-FASI, analytes injected throughout the capillary were concentrated on the basis of LVSEP, followed by an electrokinetic introduction of concentrated analytes from the inlet vial by the FASI mechanism. After switching the inlet vial solution from the sample to running buffer, the concentrated analytes were then separated by CZE. In the present LVSEP-FASI-CZE, pressure was applied to the capillary inlet until the inlet vial solution was exchanged. The applied pressure generated a counterflow against the EOF. It kept the stacked sample zone within the capillary, minimizing loss of concentrated analytes. Fluorescein was first analyzed by LVSEP-FASI-CZE to optimize preconcentration condition. Up to 110 000-fold sensitivity increase was obtained with 200 μL of sample, compared to normal CZE with sample injection of 0.3 psi for 3 s (ca. 1.7 nL). From the results, the pressure application improved the efficiency of the FASI-mode concentration significantly at total concentration time longer than 10 min. In the analysis of maltoheptaose, a 10 000-fold sensitivity increase was achieved, which is the highest concentration efficiency ever reported in CE of oligosaccharides. The relative standard deviations of the detection time and peak height were 2.4 and 11%, respectively. In the analysis of glucose oligomer, up to 8600-fold sensitivity increases were achieved without reducing the separation performance of conventional CZE.

Large-volume sample stacking for in vivo monitoring of trace levels of γ-aminobutyric acid, glycine and glutamate in microdialysates of periaqueductal gray matter by capillary electrophoresis with contactless conductivity detection

A new variant of large-volume sample stacking injection (LVSS) was used in the capillary electrophoresis with capacitively coupled contactless conductivity detection (CE/C(4)D) determination of the neurotransmitters γ-aminobutyric acid (GABA), glycine (Gly) and glutamate (Glu) in microdialysates of periaqueductal gray matter (PAG). The separation capillary was filled to 98% from the injection side with a sample of microdialysate in acetonitrile. Simultaneously with turning on the separation voltage, the sample zone was forced out by the background electrolyte by increasing the pressure in the terminal capillary outlet vessel. As a consequence of the stacking effect, the analyte was concentrated from the large sample volume into a narrow zone at the sample/background electrolyte boundary close to the injection end of the capillary. Under these conditions, LOD values of 9, 10 and 15nM were determined in the model samples for GABA, Gly and Glu, respectively; RSD equalled 0.5% for the migration times and 1.0-1.9% for the peak areas, respectively. In analysis of microdialysates of PAG, LOD values of 29, 29 and 37nM were determined for GABA, Gly and Glu, respectively; RSD equalled 0.5-0.7% for the migration times and 2.6-8.2% for the peak areas, respectively. The determined basal levels of the neurotransmitters in PAG microdialysates are 0.08, 4.7 and 0.8μM for GABA, Gly and Glu, respectively. Carrageenan-induced hyperalgesia increases the Gly and Glu levels and reduces GABA in PAG microdialysate. Peroral administration of paracetamol in hyperalgesia effectively reduces the Gly value and has no effect on Glu and GABA.