Capillary electrophoresis with solid-state electrochemiluminescence detector

We report capillary electrophoresis coupling to a solid-state electrochemiluminescence (ECL) detector for the first time. The solid-state ECL detector was fabricated by immobilizing the ECL reagent tris(2,2'-bipyridyl)ruthenium (TBR) in poly-(p-styrenesulfonate)-silica-poly(vinyl alcohol) grafting 4-vinylpyridine copolymer films. The excellent stability of the solid-state ECL detector in the phosphate solution satisfied application in CE. The CE with solid-state ECL detector system was characterized using tripropylamine (TPA) and proline. The influences of detection potential, the concentration of TBR in the film, and pH value of ECL buffer were investigated. The linear range for TPA and proline was 0.005-10 microM and 5-10 mM with correlation coefficients of 0.997 and 0.998, respectively. The detection limit (signal-to-noise ratio S/N = 3) was estimated to be 0.002 and 2.0 microM for TPA and proline, respectively. The relative standard deviations for 1.0 microM TPA and 1.0 mM proline were 8.7% and 7.5% with theoretical plate numbers of 70 000 and 16 000, respectively. Compared with the CE-ECL of TBR in aqueous solution, the CE coupling with solid-state ECL detector system gave the same sensitivity of analysis.     

A parallel dual-electrode detector for capillary electrophoresis

An approach to on-capillary dual-electrode detection for CE using a parallel electrode configuration has been developed. The parallel configuration provides two operating modes. In the first mode, one working electrode is held at an oxidizing potential and the second working electrode is held at a reducing potential. This results in redox cycling of analytes between the oxidized and reduced forms, enhancing sensitivity compared to single-electrode detection. In the second mode, both working electrodes are held at different oxidizing potentials. This mode provides electrochemical characterization of electrophoretic peaks. In the redox cyclying mode, signal enhancement of up to twofold was observed for the dual-electrode detection of phenolic acid standards compared to single-electrode detection. Variation in response of less than 10% from electrode to electrode was determined (at a concentration of 60 nM) indicating reproducible fabrication. LODs were determined to be as low as 5.0 nM for dual-electrode configuration. Using the dual-potential mode peak identification of targeted phenolic acids in whiskey samples were confirmed based on both migration time and current ratios.     

A low-cost light-emitting diode induced fluorescence detector for capillary electrophoresis based on an orthogonal optical arrangement

In this work, a simple and low-cost miniaturized light-emitting diode induced fluorescence (LED-IF) detector based on an orthogonal optical arrangement for capillary electrophoresis (CE) was developed, using a blue concave light-emitting diode (LED) as excitation source and a photodiode as photodetector. A lens obtained from a waste DVD-ROM was used to focus the LED light beam into an ∼80 μm spot. Fluorescence was collected with an ocular obtained from a pen microscope at 45° angle, and passed through a band-pass filter to a photodiode detector. The performance of the LED-IF detector was demonstrated in CE separations using sodium fluorescein and fluorescein isothiocyanate (FITC)-labeled amino acids as model samples. The limit of detection for sodium fluorescein was 0.92 μM with a signal-to-noise ratio (S/N) of 3. The total cost of the LED-IF detector was less than $ 50.     

Systems of capillary electrophoresis in electrochemiluminescence analysis

The results obtained in different scientific centers from 2000 to July, 2009 on the analytical application of electrogenerated chemiluminiscence in systems of capillary electrophoresis are summarized; the trend of development in this field is shown. The peculiarities of the operation of tandem systems using capillary electrophoresis with detection by electrogenerated chemiluminescence are considered, including the socalled lab-on-a-chip concept; systematized data on analytes are presented. The main problems arising in the determination of substances in liquid samples and the trends in the development of instruments for capillary electrophoresis with detection by electrogenerated chemiluminescence are discussed.     

A lamp light-emitting diode-induced fluorescence detector for capillary electrophoresis

A light-emitting diode-induced fluorescence detector (LED-FD) for capillary electrophoresis was constructed and evaluated. A lamp LED with an enhanced emission spectrum and a band pass filter was used as the excitation light source. Refractive index matching fluid (RIMF) was used in the detection cell to reduce scattering light and the noise level. The limit of detection (LOD) for fluorescein was 1.5 nM (SNR=3). The system exhibited linear responses in the range of 1 x 10(-8) to 5 x 10(-6)M (R=0.999). Application of the lamp LED-FD for the analysis of FITC-labeled ephedra herb extract by capillary electrophoresis was demonstrated.     

A collinear light-emitting diode-induced fluorescence detector for capillary electrophoresis

A novel fluorescence detector based on collinear scheme using a brightness light-emitting diode emitting at 470 nm as excitation source is described. The detector is assembled by all-solid-state optical-electronic components and coupled with capillary electrophoresis using on-column detection mode. Fluorescein isothiocyanate (FITC) and FITC-labeled amino acids and small molecule peptide as test analyte were used to evaluate the detector. The concentration limit of detection for FITC-labeled phenylalanine was 10 nM at a signal-to-noise ratio (S/N) of 3. The system exhibited good linear responses in the range of 1 × 10⁻⁷ to 2 × 10⁻⁵ M (R² = 0.999).     

Capillary electrophoresis and microchip capillary electrophoresis with electrochemical and electrochemiluminescence detection

Recent advances and key strategies in capillary electrophoresis and microchip CE with electrochemical detection (ECD) and electrochemiluminescence (ECL) detection are reviewed. This article consists of four main parts: CE-ECD; microchip CE-ECD; CE-ECL; and microchip CE-ECL. It is expected that ECD and ECL will become powerful tools for CE microchip systems and will lead to the creation of truly disposable devices. The focus is on papers published in the last two years (from 2005 to 2006).     

Simultaneous electrochemical and electrochemiluminescence detection for microchip and conventional capillary electrophoresis

A simultaneous electrochemical (EC) and electrochemiluminescence (ECL) detection scheme was introduced to both microchip and conventional capillary electrophoresis (CE). In this dual detection scheme, tris(2,2'-bipyridyl)ruthenium(II) (Ru(bpy)3(2+)) was used as an ECL reagent as well as a catalyst (in the formation of Ru(bpy)3(3+)) for the EC detection. In the Ru(bpy)3(2+)-ECL process, Ru(bpy)3(3+) was generated and then reacted with analytes resulting in an ECL emission and a great current enhancement in EC detection due to the catalysis of Ru(bpy)3(3+). The current response and ECL signals were monitored simultaneously. In the experiments, dopamine and three kinds of pharmaceuticals, anisodamine, ofloxacin, and lidocaine, were selected to validate this dual detection strategy. Typically, for the EC detection of dopamine with the presence of Ru(bpy)3(2+), a approximately 5 times higher signal-to-noise ratio (S/N) can be achieved than that without Ru(bpy)3(2+), during the simultaneous EC and ECL detection of a mixture of dopamine and lidocaine using CE separation. The results indicated that this dual EC and ECL detection strategy could provide a simple and convenient detection method for analysis of more kinds of analytes in CE separation than the single EC or ECL detection alone, and more information of analytes could be achieved in analytical applications simultaneously.     

Contactless conductivity detector array for capillary electrophoresis

A CE system featuring an array of 16 contactless conductivity detectors was constructed. The detectors were arranged along 70 cm length of a capillary with 100 cm total length and allow the monitoring of separation processes. As the detectors cannot be accommodated on a conventional commercial instrument, a purpose built set‐up employing a sequential injection manifold had to be employed for automation of the fluid handling. Conductivity measurements can be considered universal for electrophoresis and thus any changes in ionic composition can be monitored. The progress of the separation of Na⁺ and K⁺ is demonstrated. The potential of the system to the study of processes in CZE is shown in two examples. The first demonstrates the differences in the developments of peaks originating from a sample plug with a purely aqueous background to that of a plug containing the analyte ions in the buffer. The second example visualizes the opposite migration of cations and anions from a sample plug that had been placed in the middle of the capillary.     

Amperometric detector designs for capillary electrophoresis microchips

Electrochemical (EC) detection is a sensitive and miniaturisable detection mode for capillary electrophoresis (CE) microchips. Detection cell design is very important in order to ensure electrical isolation from the high separation voltage. Amperometric detectors with different designs have been developed for coupling EC detection to CE-microchips. Different working electrode alignment: in-channel or end-channel has been tested in conjunction with several materials: gold, platinum or carbon. The end-channel detector was based on a platinum or gold wire manually aligned at the exit of the separation channel. Thick- (screen-printed carbon electrode) and thin-film (sputtered gold film) electrodes have also been employed with this configuration, but with a different design that allowed the rapid replacement of the electrode. The in-channel detector was based on a gold film within the separation channel. A gold-based dual electrode detector, which combined for the first time in- and end-channel detection, has been also tested. These amperometric detectors have been evaluated in combination to poly(methylmethacrylate) (PMMA) and Topas (thermoplastic olefin polymer of amorphous structure) CE-microchips. Topas is a new and promising cyclic olefin copolymer with high chemical resistance. Relevant parameters of the polymer microchip separation such as precision, efficiency or resolution and amperometric detection were studied with the different detector designs using p-aminophenol and L-ascorbic acid as model analytes in Tris-based buffer pH 9.0.     

Wall-jet conductivity detector for microchip capillary electrophoresis

A new end-column ‘hybrid’ contactless conductivity detector for microchip capillary electrophoresis (CE) was developed. It is based on a “hybrid” arrangement where the receiving electrode is insulated by a thin layer of insulator and placed in the bulk solution of the detection reservoir of the chip, whereas the emitting electrode is in contact with the solution eluted from the channel outlet in a wall-jet arrangement. The favorable features of the new detector including the high sensitivity and low noise, can be attributed to both the direct contact of the ‘emitting’ electrode with the analyte solution as well as to the insulation of the detection electrode from the high DC currents in the electrophoretic circuit. Such arrangement provides a 10-fold sensitivity enhancement compared to currently used on-column contactless conductivity CE microchip detector as well as low values of noise and easy operation. The new design of the wall-jet conductivity detector was tested for separation of explosive-related methylammonium, ammonium, and sodium cations. The new detector design reconsiders the wall-jet arrangement for microchip conductivity detection in scope of improved peak symmetry, simplified study of inter-electrode distance, isolation of the electrodes, position of the wall-jet electrode to the separation channel, baseline stability and low limits of detection.     

An end-channel amperometric detector for microchip capillary electrophoresis

An end-channel amperometric detector with a guide tube for working electrode was designed and integrated on a home-made glass microchip. The guide tube was directly patterned and fabricated at the end of the detection reservoir, which made the fixation and alignment of working electrode relatively easy. The fabrication was carried out in a two-step etching process. A 30 μm carbon fiber microdisk electrode and Pt cathode were also integrated onto the amperometric detector. The characteristics and primary performance of the home-made microchip capillary electrophoresis (MCCE) were investigated with neurotransmitters. The baseline separation of dopamine (DA), catechol (CA) and epinephrine (EP) was achieved within 80 s. Separation parameters such as injection time, buffer components, pH of the buffer were studied. Relative standard deviations of not more than 6.0% were obtained for both peak currents and migration times. Under the selected separation conditions, the response for DA was linear from 5 to 200 μM and from 20 to 800 μM for CA. The limits of detection of DA and CA were 0.51 and 2.9 μM, respectively (S/N=3).     

Combination of amperometric detector & UV detector for capillary electrophoresis

A new electrochemical cell assembly with the combination of UV and amperometric detector (AD) based on their complementarity was described. A Nafion tubing junction was used to decouple the high voltage from the separation capillary in the rear of on-column UV detector. In this mode, the electroactive and inert compounds could be detected by UV and AD at the same time. Aromatic amines were determined with the UV and the end-column AD detection to evaluate the performances of the cell assembly. Such an improved electrochemical detector could match the capillary with different diameters. By simple adjustment of the screws, the positioning of the working electrode and the detection capillary was easily gained without microscope. It is also very easy to assemble and disassemble the working electrode when needed.     

Improved dual photometric-contactless conductometric detector for capillary electrophoresis

A new design of a dual, UV photometric - contactless conductometric detector is described. The separation capillary with an optical window created is pressed onto two semitubular electrodes, 3 mm wide and 2 mm apart. The electrodes form the detection cell of the contactless conductometric detector. An optical fiber, placed in the gap between the conductometric electrodes, brings radiation from the source. The radiation that passes through the separation capillary is recorded by a large-area photodiode. The optical fiber and the photodiode operate the photometric cell which is between the conductometric electrodes. The detector thus permits simultaneous photometric and conductometric detection in the same place of the capillary, while exchanging of the separation capillary is easy and without effect on the detector geometry and performance.     

Microchip capillary electrophoresis coupled with an end-column electrochemiluminescence detection

An easy and universal wall-jet configuration for microchip CE-ECL detection system was constructed and investigated in this work. Two detection modes of pre-column and post-column were applied to the above system. TPA, tramadol and lidocaine were chosen as model analytes to estimate the system in both modes. The important operational parameters such as the concentration of luminescent reagent and the distance between the separation outlet and the working electrode were optimally obtained and compared for the first time.     

Tris(2,2'-bipyridyl)ruthenium(II)-zirconia-Nafion composite films applied as solid-state electrochemiluminescence detector for capillary electrophoresis

The major goal of this work was to develop a new solid-state electrochemiluminescence (ECL) detector suitable for capillary electrophoresis (CE). The detector was fabricated by coating a sol-gel derived zirconia (ZrO(2))-Nafion composite film on a graphite electrode, then the zirconia-Nafion modified electrode was immersed in tris(2,2'-bipyridyl)ruthenium(II) (Ru(bpy)(3) (2+)) solution to immobilize this active chemiluminescence reagent. The voltammetric and ECL behaviors of the detector were investigated and optimized in tripropylamine solution. The ratio of 53% for zirconia in the zirconia-Nafion composite provided the highest luminescence intensity of immobilized Ru(bpy)(3) (2+). The ECL can maintain its stability very well in the phosphate solution in the period of 5-90 h when the solid-state ECL detector was immersed in the solution all the time. The optimum distance of capillary outlet to the solid-state ECL detector has been found to be ca. 50-80 microm for a 75 microm capillary. The effects of ionic strength and pH of ECL solution on peak height were investigated. The CE with solid-state ECL detector system was successfully used to detect tripropylamine, lidocaine, and proline. The detection limits (S/N = 3) were 5 x 10(-9) mol.L(-1) for tripropylamine, 1 x 10(-8) mol.L(-1) for lidocaine and 5 x 10(-6) mol.L(-1) for proline, and the linear ranges were from 1.0 x 10(-8) to 1.0 x 10(-5) mol.L(-1) for tripropylamine, 5.0 x 10(-7) mol.L(-1) to 1.0 x 10(-5) mol.L(-1) for lidocaine and 1.0 x 10(-5) to 1.0 x 10(-3) mol.L(-1) for proline, respectively.     

New technique for capillary electrophoresis directly coupled with end-column electrochemiluminescence detection

A new end-column electrochemiluminescence (ECL) detection technique coupling to capillary electrophoresis (CE) is characterized. A 300 microm diameter Pt working electrode was used to directly couple with a 75 microm inner diameter separation capillary without an electric field decoupler. The hydrodynamic cyclic voltammogram (CV) of Ru(bpy) 3 2+ showed that electrophoretic current did not affect the ECL reaction. The presence of high-voltage (HV) field only resulted in the shift of the ECL detection potential. The distance of capillary to electrode was an important parameter for optimizing detection performance as it determined the characteristics of mass transport toward the electrode and the actual concentration of Ru(bpy) 3 2+ in the detection region. The optimum distance of capillary to electrode was decided by the inner diameter of the capillary, too. For a 75 microm capillary, the working electrode should be placed away from the capillary outlet at a distance within the range of 220-260 microm. The effects of pH value of ECL solution and molecular structure of analytes on peak height and theoretical plate numbers were discussed. Using the 75 microm capillary, under the optimum conditions, the method provided a linear range for tripropylamine (TPA) between 1 x 10(-10) and 1 x 10(-5) mol/L with correlation coefficient of 0.998. The detection limit (signal-to-noise ratio S/N = 3) was 5.0 x 10(-11) mol/L. The relative standard deviation in peak height for eight consecutive injections was 5.6%. By this new technique lidocaine spiked in a urine sample was determined. The method exhibited the linear range for lidocaine from 5.0 x 10(-8) to 1.0 x 10(-5) mol/L with correlation efficient of 0.998. The limit of detection (S/N = 3) was 2.0 x 10(-8) mol/L.     

Determination of mefenacet by capillary electrophoresis with electrochemiluminescence detection

Electrochemiluminescence (ECL) detection with capillary electrophoresis (CE) separation system was used to the rapid analysis of mefenacet within 7 min. The linear response range of mefenacet was from 1.07 × 10⁻⁸ to 5.0 × 10⁻⁷ M with a detection limit of 4.0 × 10⁻⁹ M. This technique was also applied to analyze residues of mefenacet in seedling and soil.     

毛细管电泳电致化学发光法测定洛贝林的研究

基于稀土掺杂类普鲁士蓝化学修饰电极对Ru(bpy)32 的电催化氧化可增敏电致发光信号,建立了一种毛细管电泳-电致化学发光测定洛贝林的新方法。研究了工作电极电位、缓冲液的酸度及其浓度、分离电压和进样时间等实验参数对洛贝林测定的影响。在优化的实验条件下,其线性范围为1.5×10-7mol/L~1.5×10-4mol/L,检出限(S/N=3)为5.0×10-8mol/L。本法可直接用于注射液和空白人尿中洛贝林的测定,回收率为98.3%~101.2%。     

A novel electromagnetic induction detector with a coaxial coil for capillary electrophoresis

A novel electromagnetic induction detector with two inductors for CE was described here.The two inductors were used as signal detection and reference,respectively.The parameters affecting the detector performance(including coil turns,detection distance, excitation frequency,voltage,etc.) were optimized.Under the optimum condition,the feasibility of the detector was examined by analyzing inorganic ions.The fabricated detector showed good linear relationship between the response and the analytes concentrations,with a detection limit of 13μmol/L for Na~+(S/N = 3).A variety of advantages,such as simple construction, ease of operation,and considerably universal response,suggested this novel detector a promising application prospect in analytical area.