Microchip Capillary Electrophoresis‐Electrochemistry with Rigid Graphite‐Epoxy Composite Detector

A new rigid graphite‐epoxy composite electrode for electrochemical detection in microchip electrophoresis is described. The end‐column wall‐jet detection design relying on tubular rigid composite working electrode shows favorably low noise level and high signal‐to‐noise ratio when compared to glassy carbon detector. The performance of rigid graphite‐epoxy composite detector was compared to glassy carbon detector using dopamine and catechol as model analytes. The various parameters of the microchip electrophoresis‐rigid graphite‐epoxy composite detector were optimized.     

Enantioselective micellar electrokinetic chromatography of dl‐amino acids using (+)‐1‐(9‐fluorenyl)‐ethyl chloroformate derivatization and UV‐induced fluorescence detection

Chiral analysis of dl ‐amino acids was achieved by micellar electrokinetic chromatography coupled with UV‐excited fluorescence detection. The fluorescent reagent (+)‐1‐(9‐fluorenyl)ethyl chloroformate was employed as chiral amino acid derivatizing agent and sodium dodecyl sulfate served as pseudo‐stationary phase for separating the formed amino acid diastereomers. Sensitive analysis of (+)‐1‐(9‐fluorenyl)ethyl chloroformate‐amino acids was achieved applying a xenon‐mercury lamp for ultraviolet excitation, and a spectrograph and charge‐coupled device for wavelength‐resolved emission detection. Applying signal integration over a 30 nm emission wavelength interval, signal‐to‐noise ratios for derivatized amino acids were up to 23 times higher as obtained using a standard photomultiplier for detection. The background electrolyte composition (electrolyte, pH, sodium dodecyl sulfate concentration, and organic solvent) was studied in order to attain optimal chemo‐ and enantioseparation. Enantioseparation of 12 proteinogenic dl ‐amino acids was achieved with chiral resolutions between 1.2 and 7.9, and detection limits for most derivatized amino acids in the 13–60 nM range (injected concentration). Linearity (coefficients of determination > 0.985) and peak‐area and migration‐time repeatabilities (relative standard deviations lower than 2.6 and 1.9%, respectively) were satisfactory. The employed fluorescence detection system provided up to 100‐times better signal‐to‐noise ratios for (+)‐1‐(9‐fluorenyl)ethyl chloroformate‐amino acids than ultraviolet absorbance detection, showing good potential for d ‐amino acid analysis.     

Study of the peak broadening due to detection in the electrophoretic separation of DNA by CE and microchip CE and the application of image sensor for ultra‐small detection cell length

Narrow peaks are important to high‐resolution and high‐speed separation of DNA fragments by capillary electrophoresis and microchip capillary electrophoresis. Detection cell length is one of the broadening factors, which is often ignored in experiments. However, is it always safe to neglect detection cell length under any condition? To answer this question, we investigated the influence of detection cell length by simulation and experiments. A parameter named as detection cell length ratio was proposed to directly compare the detection cell length and the spatial length of sample band. Electrophoretic peaks generated by various detection cell length ratios were analyzed. A simple rule to evaluate the peak broadening due to detection cell length was obtained. The current states of the detection cell length of detection system and their reliabilities in capillary electrophoresis and microchip capillary electrophoresis were analyzed. Microchip capillary electrophoresis detection with an ultra‐small detection cell length of 0.36 μm was easily achieved by using an image sensor.     

Single photo-electron and photon detection in a mercury resonance ionization photon detector (RID)

Avalanche detection of a laser enhanced ionization (LEI) signal has been studied in a resonance ionization detector (RID) cell containing mercury vapor at room temperature. An avalanche multiplication factor of more than 8000 was achieved. The limit of detection of Hg resonance radiation (λ = 253.7 nm) was at the level of 0.5 quantum during the lifetime of the excited 6³P₁⁰ state. Detection of radiation from a conventional CW Hg discharge lamp source with a signal to noise ratio of more than 10⁴ has been achieved.     

Detection systems for mass spectrometry imaging: A perspective on novel developments with a focus on active pixel detectors

Instrumental developments for imaging and individual particle detection for biomolecular mass spectrometry (imaging) and fundamental atomic and molecular physics studies are reviewed. Ion‐counting detectors, array detection systems and high mass detectors for mass spectrometry (imaging) are treated. State‐of‐the‐art detection systems for multi‐dimensional ion, electron and photon detection are highlighted. Their application and performance in three different imaging modes – integrated, selected and spectral image detection – are described. Electro‐optical and microchannel‐plate‐based systems are contrasted. The analytical capabilities of solid‐state pixel detectors – both charge coupled device (CCD) and complementary metal oxide semiconductor (CMOS) chips – are introduced. The Medipix/Timepix detector family is described as an example of a CMOS hybrid active pixel sensor. Alternative imaging methods for particle detection and their potential for future applications are investigated. Copyright © 2012 John Wiley & Sons, Ltd.     

Simultaneous determination of caffeine,paracetamol, and ibuprofen in pharmaceutical formulations by high‐performance liquid chromatography with UV detection and by capillary electrophoresis with conductivity detection

Paracetamol, caffeine and ibuprofen are found in over‐the‐counter pharmaceutical formulations. In this work, we propose two new methods for simultaneous determination of paracetamol, caffeine and ibuprofen in pharmaceutical formulations. One method is based on high‐performance liquid chromatography with diode‐array detection and the other on capillary electrophoresis with capacitively coupled contactless conductivity detection. The separation by high‐performance liquid chromatography with diode‐array detection was achieved on a C₁₈ column (250×4.6 mm², 5 μm) with a gradient mobile phase comprising 20–100% acetonitrile in 40 mmol L^?1 phosphate buffer pH 7.0. The separation by capillary electrophoresis with capacitively coupled contactless conductivity detection was achieved on a fused‐silica capillary (40 cm length, 50 μm i.d.) using 10 mmol L^?1 3,4‐dimethoxycinnamate and 10 mmol L^?1 β‐alanine with pH adjustment to 10.4 with lithium hydroxide as background electrolyte. The determination of all three pharmaceuticals was carried out in 9.6 min by liquid chromatography and in 2.2 min by capillary electrophoresis. Detection limits for caffeine, paracetamol and ibuprofen were 4.4, 0.7, and 3.4 μmol L^?1 by liquid chromatography and 39, 32, and 49 μmol L^?1 by capillary electrophoresis, respectively. Recovery values for spiked samples were between 92–107% for both proposed methods.     

Capillary Electrophoresis for the Simultaneous Determination of Metals by Using Ethylenediamine Tetraacetic Acid as Complexing Agent and Vancomycin as Complex Selector

A new separation system of capillary electrophoresis for the simultaneous determination of metals by using ethylenediamine tetraacetic acid （EDTA） as complexing agent and employing vancomycin as complex selector was described. The Z-shape cell capillary electrophoresis was used to enhance the sensitivity for the determination of the complexes of Cu（Ⅱ）, Ni（Ⅱ）, Co（Ⅱ） and Fe（Ⅲ） with EDTA. The partial filling method （co-current mode） was used in order to increase the selectivity of the electrophoretic method, meanwhile vancomycin was not present at the detector path during the detection of metal-EDTA complexes. The vancomycin concentration, phosphate concentration and pH of the buffer strongly influenced mobility, resolution and selectivity of the studied analytes. Under the optimal condition, the relative standard deviations （n=5） of the migration time and the peak area were less than 3.14% and 7.35%, respectively. Application of the Z-shape cell capillary electrophoresis method with UV detection and vancomycin loading led to the reliable determination of these metal ions in tap water and the recoveries were 97%-101%. The detection limits based on a signal to noise ratio of 3 ： 1 were found in the range of 2-10 μg·L^-1.     

Nanoband electrode for high-performance in-channel amperometric detection in dual-channel microchip capillary electrophoresis

A nanoband electrode detector integrated with a dual-channel polydimethylsiloxane microchip is proposed for in-channel amperometric detection in microchip capillary electrophoresis. Gold nanoband electrodes, which were fabricated on SU-8 substrates with a 100-nm-width gold layer, were introduced into the dual-channel microchip to be an electrochemical detector. Due to the nano-sized width of the detector, the noise of the amperometric detection was significantly reduced, and a high separation resolution was achieved for monitoring the analytes. The detection sensitivity of the system was improved by high signal-to-noise ratio, and a low detection limit on microchip was obtained for p-aminophenol (2.09 nM). Because of the high resolution in measuring half-peak width, the plate number that is used to evaluate the separation efficiency was 1.5-fold higher than that using 50-μm-width electrochemical detector. The effect of sample injection time and data acquisition time on separation efficiency was investigated, and an attractive separation efficiency was achieved with a plate number up to 17,500.     

Fast parallel detection of feline panleukopenia virus DNA by multi‐channel microchip electrophoresis with programmed step electric field strength

A multi‐channel microchip electrophoresis using a programmed step electric field strength (PSEFS) method was investigated for fast parallel detection of feline panleukopenia virus (FPV) DNA. An expanded laser beam, a 10× objective lens, and a charge‐coupled device camera were used to simultaneously detect the separations in three parallel channels using laser‐induced fluorescence detection. The parallel separations of a 100‐bp DNA ladder were demonstrated on the system using a sieving gel matrix of 0.5% poly(ethylene oxide) (M_r = 8 000 000) in the individual channels. In addition, the PSEFS method was also applied for faster DNA separation without loss of resolving power. A DNA size marker, FPV DNA sample, and a negative control were simultaneously analyzed with single‐run and one‐step detection. The FPV DNA was clearly distinguished within 30 s, which was more than 100 times faster than with conventional slab gel electrophoresis. The proposed multi‐channel microchip electrophoresis with PSEFS was demonstrated to be a simple and powerful diagnostic method to analyze multiple disease‐related DNA fragments in parallel with high speed, throughput, and accuracy.     

Amperometric Sniffer Based on Electrodes Supported on Ion‐Exchangers for Monitoring the State of Turning Rancid of Lipids

A porous gold electrode supported on one face of an ion‐exchange membrane, acting as a solid polymer electrolyte (SPE), is proposed as an amperometric sniffer for monitoring the aldehyde content in the headspace in equilibrium with lipid samples, in order to gain indication of their state of turning rancid It was used as a detector for a flow injection system in which aldehydes were injected, after preconcentration by solid phase microextraction on a SPME fiber from the gas phase standing above thermostated samples and subsequent desorption by heating. Repeatable (±4.5%) sharp peaks were detected over a wide linear concentration range (0.5–200 ppm). A detection limit of about 0.03 ppm was inferred for a signal‐to‐noise ratio of 3, referred to hexylaldehyde (used as prototype) dissolved in squalene or vegetable oils samples. This approach was applied to the determination of volatile aldehydes from some partially oxidized cereal oils and the results found were compared with both the corresponding peroxide values and their aldehyde content determined by a conventional spectrophotometric method.     

Determination of iron in real samples by high performance capillary electrophoresis in combination with thermal lensing

Natural iron concentrations in real water samples have been determined by thermal lensing as a high performance capillary electrophoresis detector. 1,10-Phenanthroline was used as a chromogenic reagent, which forms a stable complex with Fe(II) but not with Fe (III). The interferences by other cations can be neglected by a combination of this photometric technique with high performance capillary electrophoresis. Laser induced thermal lens spectroscopy is demonstrated as a new technique for the measurement of small absorbances in the picoliter detection volume of a capillary. A limit of detection of 36 nmol/L with a signal to noise ratio of 7?:?1 was achieved using a 75 μm fused silica capillary.     

Chemiluminescent detection of amines and amino acids using in situ generated Ru(bpy)(3)(3+) following separation by capillary electrophoresis

A new sensitive chemiluminescent detection method for capillary electrophoresis is described. Underivatized amines and amino acids were detected following capillary electrophoresis separation by their chemiluminescent reaction with Ru(bpy)(3)(3+) generated in situ at 35 mum carbon fibers. Detection limits for triethylamine and proline were 5 and 3 fmol, respectively at a SNR of three. The noise limiting the detectability of separated analytes was determined to exist at the level of the dark noise limit of the PMT used for these studies and additional noise reduction strategies are expected to improve the quantitative aspects of the method. Theoretical plate numbers for proline were approximately 20 000. End column addition of Ru(bpy)(3)(2+) coupled with in situ generation of Ru(bpy)(3)(3+), has been shown to be compatible with the nanoliter elution volumes characteristic of capillary electrophoresis.     

Absorbance detector based on a deep UV light emitting diode for narrow‐column HPLC

A detector for miniaturized HPLC based on deep UV emitting diodes and UV photodiodes was constructed. The measurement is accomplished by the transverse passage of the radiation from the light‐emitting diode (LED) through fused‐silica tubing with an internal diameter of 250 μm. The optical cell allows flexible alignment of the LED, tubing, and photodiode for optimization of the light throughput and has an aperture to block stray light. A beam splitter was employed to direct part of the emitted light to a reference photodiode and the Lambert–Beer law was emulated with a log‐ratio amplifier circuitry. The detector was tested with two LEDs with emission bands at 280 and 255 nm and showed noise levels as low as 0.25 and 0.22 mAU, respectively. The photometric device was employed successfully in separations using a column of 1 mm inner diameter in isocratic as well as gradient elution. Good linearities over three orders of magnitude in concentration were achieved, and the precision of the measurements was better than 1% in all cases. Detection down to the low micromolar range was possible.     

Graphene/poly(ethylene‐co‐vinyl acetate) composite electrode fabricated by melt compounding for capillary electrophoretic determination of flavones in Cacumen platycladi

In this report, a graphene/poly(ethylene‐co‐vinyl acetate) composite electrode was fabricated by melt compounding for the amperometric detection of capillary electrophoresis. The composite electrode was fabricated by packing a mixture of graphene and melted poly(ethylene‐co‐vinyl acetate) in a piece of fused silica capillary under heat. The structure of the composite was investigated by scanning electron microscopy and Fourier transform infrared spectroscopy. The results indicated that graphene sheets were well dispersed in the composite to form an interconnected conducting network. The performance of this unique graphene‐based detector has been demonstrated by separating and detecting rutin, quercitrin, kaempferol, and quercetin in Cacumen platycladi in combination with capillary electrophoresis. The four flavones have been well separated within 9 min in a 50‐cm‐long capillary at a separation voltage of 12 kV using a 50 mM sodium borate buffer (pH 9.2). The graphene‐based detector offered significantly lower operating potentials, substantially enhanced signal‐to‐noise characteristics, lower expense of operation, high resistance to surface fouling, and enhanced stability. It showed long‐term stability and repeatability with relative standard deviations of <5% for the peak current (n = 15).     

高效毛细管电泳-电荷耦合器件检测器联用技术研究Ⅳ.Monte Carlo模拟

根据毛细管电泳分离受不确定因素影响较多的特点，应用MonteCarlo模拟方法，探讨了电荷耦合器件检测器操作参数，进样、电压、温度等误差因素对检测信号强度、测定准确度和精密度的影响，比较了峰高和峰体积定量计算方法的相对优劣，对进一步开发和应用电荷耦合器件检测毛细管电泳技术有一定意义。     

Noise normalisation in capillary electrophoresis using a diode array detector

When using capillary electrophoresis with a diode array detector, the wavelength at maximum absorbance is often chosen to quantify a given analyte. However, the background noise for every wavelength should be taken into account as it is by maximising the signal to noise ratio that the lowest limit of detection will be obtained. Here, we proposed an algorithm allowing to correct an electropherogram from its background absorption and to estimate the background noise. Applying it to all the electropherograms obtained in each wavelength channel allows obtaining the background noise as a function of the wavelength, which can be used to calculate the signal to noise ratio. This not only allows selecting the best wavelength to maximise the limit of detection of a given analyte, but also to generate a noise normalised base peak electropherogram (nn-BPE). It is shown that the noise normalised base peak electropherograms substantially improve the peaks visualisation. The algorithm is part of a graphic user interface that runs under MatLab environment; it does not require any programming knowledge and is freely available.     

Interpretation on Band‐Broadening in Chromatography with Spatial Peak Profiles Obtained Using Whole‐Column Detection

Fifteen liquid chromatographic experiments were investigated using a whole‐column detection (WCD) system and a conventional post‐column UV/Vis detector. The peak widths obtained from chromatograms were found dependent on the retention factor; the larger the retention factor was the greater the peak width. However, the on‐column spatial peak widths were dependent on the locations where they were measured in the column. The peak widths monitored at 17 cm from the column inlet were found essentially the same no matter what their retention factors were. In addition, a linear relationship was found between the chromatographic peak width and the reciprocal of the average linear rate of the solute migration. The peak widths on chromatograms did not reflect how they appeared in the column; instead, the widths were determined by the solute speed passing the detector.     

Development and validation of a capillary electrophoresis method for the characterization of sulfoethyl cellulose

To characterize sulfoethyl cellulose el samples, a capillary electrophoresis method was developed and validated sulfoethyl cellulose el was hydrolyzed, and the resulting d ‐glucose derivatives were analyzed after reductive amination with 4‐aminobenzoic acid using 150 mM boric acid, pH 9.5, as background electrolyte at 20°C and a voltage of 28 kV. Peak identification was derived from capillary electrophoresis with mass spectrometry using 25 mM ammonia adjusted to pH 6.2 by acetic acid as electrolyte. Besides mono‐, di‐, and trisulfoethyl d ‐glucose small amounts of disaccharides could be identified resulting from incomplete hydrolysis. The linearity of the borate buffer‐based capillary electrophoresis method was evaluated using d ‐glucose in the concentration range of 3.9–97.5 μg/mL, while limits of detection and quantification derived from the signal‐to‐noise ratio of 3 and 10 were 0.4 ± 0.1 and 1.2 ± 0.3 μg/mL, respectively. Reproducibility and intermediate precision were determined using a hydrolyzed sulfoethyl cellulose el sample and ranged between 0.2 and 8.8% for migration times and between 0.3 and 10.4% for peak area. The method was applied to the analysis of the degree of substitution of synthetic sulfoethyl cellulose el samples obtained by variation of the synthetic process and compared to data obtained by elemental analysis.     

Rapid chiral on-chip separation with simplified amperometric detection

The enantiomers of adrenaline, noradrenaline, ephedrine and pseudoephedrine were separated by capillary electrophoresis on a micromachined device. Detection was carried out with a new two-electrode amperometric detector, eliminating the need for individual counter and reference electrodes. Separation of the isomers was achieved by employing carboxymethyl-beta-cyclodextrin as chiral selector in the buffer, partly with the additional inclusion of the crown ether 18-crown-6. Plate numbers of up to 20,000, chiral resolutions of 2.5 and detection limits of the order of 10(-7) M were achieved. All separations were completed in less then 3 min.     

Capacitance‐to‐digital: The upgrades of single chip detector

The capacitance‐to‐digital single chip detector was upgraded. The paper discusses hardware issues and benefits of the designed/upgraded detector. The device can be operated from rechargeable lithium‐ion battery as stand‐alone, portable system and is capable of transmitting real‐time data wirelessly. The detector and additional modules (battery, battery holder, microcontroller board, wireless module) weight is less than 85 g. Electrophoretic separation in low conductivity 20 mM MES/L‐His buffer, pH 6.1, was performed in order to evaluate detection parameters. The system is capable of quantification of potassium ions down to 0.31 μM. Investigation of differential signal acquisition configuration showed improved performance regarding external noise and temperature fluctuations. The system can be a solution for stand‐alone, field‐portable capillary format separation detector.