Light-emitting diode-based indirect fluorescence detection for simultaneous determination of anions and cations in capillary electrophoresis

Simultaneous capillary electrophoresis of anions and cations in a single injection using an anion exchanger-modified capillary for determination of salivary ions in combination with statistical analyses

This paper describes the simultaneous capillary electrophoresis (CE) of anions and cations using an anion exchange-modified capillary, which was prepared by chemical coating with a cationic silylating reagent, and its application to saliva analysis. The CE method provides high-throughput (5 min for a single sample injection) analysis by generating a high-velocity electroosmotic flow at pH 3.0-3.5. The detection limits at a signal-to-noise ratio of 3 ranged from 1.2 to 18 μM for anions and 1.0 to 2.7 μM for cations. The relative standard deviations for the migration times and peak areas of analytes (n = 4) ranged from 0.05% to 0.40% and 0.94% to 4.7%, respectively. The CE system was used to analyze 11 common ions in saliva samples collected from long-distance runners and sedentary university students before and after running for a set distance or a set time. Interestingly, the SCN^- concentrations decreased in the saliva samples of all 14 athletes and 16 sedentary students after running. Furthermore, when the concentrations of the analyzed ions were compared with that of cortisol as a typical stress marker by multiple regression analysis, SCN^- and NO₃^- in saliva samples from the two subject groups strongly correlated with cortisol levels, as determined by an electrochemiluminescence immunoassay. This study improves our knowledge of both the analytical methodology for CE and statistical methods for identifying common ions that could be used as physical stress markers.

Separation of amino acids by capillary electrophoresis with light-emitting diode-induced fluorescence in the presence of electroosmotic flow

In this chapter, we describe a method to identify amino acids (AA) by capillary electrophoresis in conjunction with light-emitting diode-induced fluorescence (LEDIF). First, amino acids labeled with naphthalene-2,3-dicarboxaldehyde (NDA) in the presence of cyanide are converted to highly fluorescent cyanobenz[f]isoindole (CBI) derivatives. Next, they are separated by gel electrophoresis in the presence of EOF. In the process, the CBI products were excited by a violet LED to produce green fluorescence. In addition to the optical setup of light-emitting diode-induced fluorescence, the preparation of poly(ethylene) oxide for amino acid separation is also described in this chapter.

Simultaneous determination of uranium carbide dissolution products by capillary zone electrophoresis

Separation and simultaneous determination of a number of organic acid anions (oxalate, mellitate, trimellitate and benzoate) and U(VI) with direct UV detection is developed for analysis of uranium carbide (UC) dissolution products by capillary zone electrophoresis (CZE). Reverse polarity mode is used. It is found that complex formation of U(VI) with carbonate, used as a carrier electrolyte, allows U(VI) to be determined, as negatively charged species, in a single run with organic acid anions. Some parameters such as pH value, composition of electrolyte and detection wavelength are optimized. Under the chosen conditions (carbonate buffer (ionic strength of 100 mM), pH 9.8, 0.15 mM tetradecyltrimethylammonium bromide (TTAB)) a complete separation is achieved. Calibration plots are linear in two ranges of concentration for U(VI) ( approximately 1 x 10(-5) to 1 x 10(-3)), mellitate and trimellitate ( approximately 5 x 10(-6) to 5 x 10(-4)), and about one range ( approximately 1 x 10(-4) to 5 x 10(-3)) for oxalate and benzoate. Accuracy of the procedure is checked by the "added-found" method in standard mixture solutions. Relative standard deviation is within the range of 2-10% and the recovery is in the range of 90-110%. This method is applied for the analysis of real UC dissolution samples.

Absorbance Based Light Emitting Diode Optical Sensors and Sensing Devices

The ever increasing demand for in situ monitoring of health, environment and security has created a need for reliable, miniaturised sensing devices. To achieve this, appropriate analytical devices are required that possess operating characteristics of reliability, low power consumption, low cost, autonomous operation capability and compatibility with wireless communications systems. The use of light emitting diodes (LEDs) as light sources is one strategy, which has been successfully applied in chemical sensing. This paper summarises the development and advancement of LED based chemical sensors and sensing devices in terms of their configuration and application, with the focus on transmittance and reflectance absorptiometric measurements.

An evaluation of the experimental approaches to detection of small ions in CE

This review points out some important trends in the development of the detection techniques for small ions in CE. On the basis of selected literature references it briefly discusses some general requirements on detection techniques in CE. Various optical measurements, mass spectrometric approaches and electrochemical detection techniques are dealt with. Some specific features of microchip CE separation and detection are pointed out and possibilities of dual detection are mentioned. The principal parameters of the above detection techniques are then briefly compared.

CE with sequential light-emitting diode-induced fluorescence and electro-chemiluminescence detections for the determination of amino acids and alkaloids

This paper describes the determination of alkaloids and amino acids (AAs) using CE in conjunction with sequential light-emitting diode-induced fluorescence (LEDIF) and electrochemiluminescence (ECL) detections. In the CE-LEDIF-ECL system, the ECL detector was located in the outlet of the capillary, while the LEDIF detector was positioned 12 cm from the outlet. Naphthalene-2,3-dicarboxaldehyde (NDA) was used to form fluorescent AA-NDA derivatives from AAs possessing primary amino groups, while Ru(bpy)(3) (2+) was used to obtain ECL signals for analytes having secondary and tertiary amino groups. In the presence of poly(ethylene oxide), we accomplished the CE-LEDIF-ECL separation of a mixture of 12 AA-NDA derivatives, anabasine, nicotine, and proline within 11 min. This low-cost CE-LEDIF-ECL system allows the analysis of these AA-NDA derivatives and alkaloids at concentrations in the ranges of 49 nM-0.2 microM and 0.66-4.7 microM, respectively. We applied our CE-LEDIF-ECL system to the analysis of a urine sample and also to tobacco extracts. We obtained good qualitative and quantitative results when using this method with these analytes: the RSDs were below 3.0 and 2.8%, respectively. This CE-LEDIF-ECL system provides the advantages of high efficiency, speed, and sensitivity for the analysis of analytes possessing amino groups.

Method development for the determination of coumarin compounds by capillary electrophoresis with indirect laser-induced fluorescence detection

A capillary zone electrophoresis (CZE) with indirect laser-induced fluorescence detection (ILIFD) method is described for the simultaneous determination of esculin, esculetin, isofraxidin, genistein, naringin and sophoricoside. The baseline separation was achieved within 5 min with running buffer (pH 9.4) composed of 5mM borate, 20% methanol (v/v) as organic modifier, 10(-7)M fluorescein sodium as background fluorophore and 20 kV of applied voltage at 30 degrees C of cartridge temperature. Good linearity relationships (correlation coefficients >0.9900) between the second-order derivative peak-heights (RFU) and concentrations of the analytes (mol L(-1)) were obtained. The detection limits for all analytes in second-order derivative electrophoregrams were in the range of 3.8-15 microM. The RSD data of intra-day for migration times and second-order derivative peak-height were less than 0.95 and 5.02%, respectively. This developed method was applied to the analysis of the courmin compounds in herb plants with recoveries in the range of 94.7-102.1%. In this work, although the detection sensitivity was lower than that of direct LIF, yet the method would extend the application range of LIF detection.

CE detector based on light-emitting diodes

CE detectors based on light-emitting diodes (LEDs) as light sources are receiving considerable attention due to their exceptionally high stability, high intensity, low cost, and a variety of wavelengths in the UV and visible spectrum. This article is a comprehensive review on CE methods using LED-based detectors with absorbance and fluorescence detection, and several applications on the determination of riboflavin, bacteria, drug, and amino acids in biological samples are described.

Capillary electrophoresis with a UV light-emitting diode source for chemical monitoring of native and derivatized fluorescent compounds

We report the utilization of a high power UV light-emitting diode for fluorescence detection (UV-LED-IF) in CE separations. CE-UV-LED-IF allows analysis of a range of environmentally and biologically important compounds, including PAHs and biogenic amines, including neurotransmitters, amino acids, proteins, and peptides, that have been derivatized with UV-excited fluorogenic labels, e.g., o-phthalic dicarboxaldehyde/beta-mercaptoethanol (OPA/beta-ME). The 365 nm UV-LED was used as a stable, low cost source for detection of UV-excited fluorescent compounds. UV-LED-IF was used with both zonal CE separations and MEKC. Native fluorescence detection of PAHs was accomplished with detection limits ranging from 10 nM to 1.3 microM. Detection limits for OPA/beta-ME-labeled glutamic acid and aspartic acid were 11 and 10 nM, respectively, for off-line labeling, and 47 and 47 nM, respectively, for on-line labeling, comparable to UV-laser-based systems. Analysis of OPA/beta-ME-labeled proteins and peptides was performed with 28 and 47 nM detection limits for BSA and myoglobin, respectively.

Comparative study between a commercial and a homemade capillary electrophoresis instrument for the simultaneous determination of aminated compounds by induced fluorescence detection

The performance of two capillary electrophoresis (CE) instruments, one commercial and one homemade device, were compared for the determination of derivatised aminated compounds with fluorescein isothiocyanate (FITC). The commercial CE system first uses an argon ion laser as excitation source; the homemade CE device uses an inexpensive blue-light-emitting diode (LED) as the light source and a charge-coupled device (CCD) as the detection system. After fine optimisation of several separation parameters in both devices, a co-electroosmotic flow CE methodology was achieved in coated capillary tubing with 0.001% hexadimetrine bromide (HDB), and 50 mmol L-1 sodium borate at pH 9.3 with 20% 2-propanol for the determination of several amines and aminoacids. Analytical performances, applicability in beer samples and other aspects such as cost or potential for miniaturization have been compared for both devices.

A scalable method for multiplex LED-controlled synthesis of DNA in capillaries

As research in synthetic biology and genomic sciences becomes more widespread, the need for diverse oligonucleotide populations has increased. To limit reagent cost, it would be advantageous to obtain high quality populations in minute amounts. Towards that end, synthesis of DNA strands in capillaries utilizing photolabile 3-nitrophenylpropyloxycarbonyl (NPPOC) chemistry and ultraviolet-light emitting diodes (UV-LEDs) was examined. Multiple oligonucleotides were made in single capillaries and were characterized by hybridization, sequencing and gene synthesis. DNA synthesized in capillaries was capable of being hybridized and signal intensities correlated with microarray data. Sequencing demonstrated that the oligonucleotides were of high quality (up to 44% perfect sequences). Oligonucleotides were combined and used successfully for gene synthesis. This system offers a novel, scalable method to synthesize high quality oligonucleotides for biological applications.

A simple light-emitted diode-induced fluorescence detector using optical fibers and a charged coupled device for direct and indirect capillary electrophoresis methods

We constructed a simple fluorescence detector for both direct and indirect CE methods using a blue light-emitted diode (470 nm) as excitation source, a bifurcated optical fiber as a waveguide, and a CCD camera as a detector. The connection of all the components is fairly easy even for nonexperts and the use of a CCD camera improves the applicability of this detector compared to the others using PMTs because it permits the recording of 2-D electropherograms or phosphorescence measurements. This detector provides a compact, low cost, and rapid system for the determination of native fluorescence compounds which have high quantum yields by CE with direct fluorescence detection, showing an LOD of 2.6 x 10(-6) M for fluorescein; the determination of fluorescence derivative compounds by CE with direct fluorescence detection, showing an LOD of 1.6 x 10(-7) M for FITC-labeled 1,6-diaminohexane; and nonfluorescence compounds by CE with indirect fluorescence detection with an LOD of 2.7 x 10(-6) M for gallic acid.

Stacking, derivatization, and separation by capillary electrophoresis of amino acids from cerebrospinal fluids

This paper describes the in-column derivatization, stacking, and separation of amino acids by CE in conjunction with light-emitting diode-induced fluorescence using naphthalene-2,3-dicarboxaldehyde (NDA). According to the relative electrophoretic mobilities and the migration direction in tetraborate solution (pH 9.3), the injection order is cyanide, then amino acids, then NDA. Once poly(ethylene oxide) (PEO) migrates through the capillary under EOF, the amino acid.NDA derivatives, amino acids, and CN- ions migrating against the EOF enter the PEO zone. As a result of increases in viscosity and possible interactions with PEO molecules, the reagents/analytes slow down such that they become stacked at the boundary. In comparison with the off-column approach to the analysis of amino acids, our proposed method provides a lower degree of interference from polymeric NDA compounds and other side products. As a result, the plot of the peak height as a function of gamma-aminobutyric acid (GABA) concentration is linear over the range from 10(-5) to 10(-8) M, with the LOD being 4 nM. We demonstrate the diagnostic potential of this approach for the determination of amino acids, including GABA and glutamine, in biological samples through the analysis of large volumes of cerebral spinal fluids without the need for sample pretreatment.

Recent advances in capillary electrophoresis and capillary electrochromatography of pollutants

Recent advances in the CE and CEC separation, detection, and sample preparation methodologies applied to the determination of a variety of compounds having current or potential environmental relevance have been overviewed. The reviewed literature has illustrated the wide range of CE applications, indicating the continuing interest in CE and CEC in the environmental field.

Low-picomolar limits of detection using high-power light-emitting diodes for fluorescence

Fluorescence detectors are ever more frequently being used with light-emitting diodes (LEDs) as the light source. Technological advances in the solid-state lighting industry have produced LEDs which are also suitable tools in analytical measurements. LEDs are now available which deliver 700 mW of radiometric power. While this greater light power can increase the fluorescence signal, it is not trivial to make proper use of this light. This new generation of LEDs has a large emitting area and a highly divergent beam. This presents a classic problem in optics where one must choose between either a small focused light spot, or high light collection efficiency. We have selected for light collection efficiency, which yields a light spot somewhat larger than the emitting area of the LED. This light is focused onto a flow cell. Increasing the detector cell internal diameter (i.d.) produces gains in (sensitivity)3. However, since the detector cell i.d. is smaller than the LED spot size, scattering of excitation light towards the detector remains a significant source of background signal. This can be minimized through the use of spectral filters and spatial filters in the form of pinholes. The detector produced a limit of detection (LOD) of 3 pM, which is roughly three orders of magnitude lower than other reports of LED-based fluorescence detectors. Furthermore, this LOD comes within a factor of six of much more expensive laser-based fluorescence systems. This detector has been used to monitor a separation from a gel filtration column of fluorescently labeled BSA from residual labeling reagent. The LOD of fluorescently labeled BSA is 25 pM.

Fabrication of an integrated PDMS microchip incorporating an LED-induced fluorescence device

A microfluidic device with an integrated fluorescence detection system has been developed in order to miniaturize the entire analytical system. A blue or green light-emitting diode (LED) and an optical fiber were mounted in a polydimethylsiloxane-based microchip. The performance of this device was evaluated by microchip electrophoresis. When a green LED was used as the light source, the calibration curve of Sulforhodamine-101 was linear over the range 1-100 microM. The detection limit was found to be 600 nM (240 amol) for a S/N ratio of 3. When using a blue LED, the calibration curve of Fluorescein was linear over the range 0.2-100 microM. The detection limit was estimated to be 120 nM (50 amol) (S/N=3). The detection sensitivity per unit power was comparable to that of LIF. The RSD values for the migration time, peak height and peak area were 0.74, 7.18 and 9.45%, respectively. The integrated microfluidic device was successfully used to determine amino acid derivatives.

Capillary electrophoresis of inorganic ions: An update

This review as a sequel of three earlier similar reports gives a summary of the progress and significant methodological developments, starting from 2002, in the use of capillary electrophoresis (CE) for inorganic ion analysis. As substantiated by the illustrative number of relevant references, improvements in sensitivity achieved both in and outside a CE system, advances in manipulating the separation selectivity, novel hardware configurations, and system performance innovations are continually being reported over the review period. Specifically viewed are the recent advancements in elemental (bio)speciation analysis, which remains one of the most fertile areas of CE research, as well as in three recently booming research topics: contactless conductivity detection, separations on microchips, and transient isotachophoretic preconcentration. A state-of-the-art picture of technique's potentialities within the field of interest presented here demonstrates that CE has become recognized and is growing in acceptance as a reliable alternative to traditional analytical methods such as high-performance liquid chromatography (HPLC).

High-power blue/UV light-emitting diodes as excitation sources for sensitive detection

With advances in III-V nitride manufacturing processes, high-power light-emitting diode (LED) chips in the blue and UV wavelengths are now commercially available at reasonable cost and can be used as excitation sources in optical sensing. We describe the use of these high-power blue and UV LEDs for sensitive fluorescence detection, including chip-based flow cytometry, capillary electrophoresis (CE), and single-molecule imaging. By using a blue LED with a focusable power of approximately 40 mW as the excitation source for fluorescent beads, we demonstrate a simple chip-based bead sorter capable of enriching the concentration of green fluorescent beads from 63% to 95%. In CE experiments, we show that a mixture of analyte solution containing 30 nM 6-carboxyrhodamine 6G and 10 nM fluorescein can be separated and detected with excellent signal-to-noise ratio (approximately 17 for 10 nM fluorescein) using the collimated emission from a blue LED; the estimated mass detection limit was approximately 200 zmol for fluorescein. We also demonstrated ultrasensitive fluorescence imaging of single rhodamine 123 molecules and individual lambda-DNA molecules. At a small fraction of the cost of an Ar+ laser, high-power blue and UV LEDs are effective alternatives for lasers and arc lamps in fluorescence applications that demand portability, low cost, and convenience.