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.     

Development and Characterization of a Disposable Electrochemical Detector Arrangement for Capillary Electrophoresis Prepared by Thermal Lamination

A disposable electrochemical detector arrangement for capillary electrophoresis has been developed. The detection system consists of an assembly of a fused silica capillary and a microfiber electrode which are fixed in a proper position by sealing this configuration with the help of thermal lamination. The detector design is easy to prepare and inexpensive. Therefore it is used as a disposable device which can be replaced by a new one if any degradation of the performance characteristics occurs. The parameters influencing the detection performance were studied and optimized using nonaqueous capillary electrophoresis and ferrocene derivatives as model compounds. The practical utility was demonstrated by studying the separation and detection of water‐resistant dye compounds.     

Rapid speciation of iron by on-line coupling of short column capillary electrophoresis and inductively coupled plasma mass spectrometry with the collision cell technique

A method for rapid speciation analysis of iron was developed by on-line coupling of short column capillary electrophoresis and inductively coupled plasma mass spectrometry. The collision cell technique was used to eliminate argon-based polyatomic interferences and a Micromist nebulizer was employed to increase the nebulization efficiency. Rapid speciation analysis of Fe(II) and Fe(III) was achieved within 1 min by short column capillary electrophoresis in a 14 cm x 50 microm id capillary at 28 kV voltage with a mixture of 15 mmol/L tris(hydroxymethyl)aminomethane + 1 mmol/L 1,10-phenanthroline + 1 mmol/L EDTA (pH 8.6) as running electrolyte. The precisions (RSD, n = 5) of migration time and peak area for Fe(II) and Fe(III) were in the range of 1.0 - 2.6 and 1.9 - 3.9%, respectively. The limits of detection (3sigma) of Fe(II) and Fe(III) were 10.0 and 8.3 microg/L, respectively.     

A simplified poly(dimethylsiloxane) capillary electrophoresis microchip integrated with a low-noise contactless conductivity detector

A contactless conductivity detector integrated into a poly(dimethylsiloxane) microchip for electrophoresis is presented. It adopted the simplest configuration of electrodes commonly used in this detection mode for capillary electrophoresis microchips. Although the chip is based on a simple and effective design, it is able to obtain low detection levels due to the low noise of the detection circuit. A circuit based on a lock-in amplifier was designed on printed circuit boards to read out the signal. The property of the detection cell was studied by applying excitation signals of different frequencies and different amplitudes. It was found that the best detection limit could be achieved with a frequency of 50?kHz and amplitude of 20?V. The performance of the detector was demonstrated by successfully separating and detecting several inorganic ions and also a mixture of heavy metal ions. An average detection limit of 0.4?μM was obtained for inorganic cations. This value is significantly improved compared to similar microchip-based detectors. The presented detector could be promising for mass production due to its properties, such as simple construction, high degree of integration, high performance and low cost.     

Recent Applications of Capillary Electrophoresis in the Determination of Active Compounds in Medicinal Plants and Pharmaceutical Formulations

The present review summarizes scientific reports from between 2010 and 2019 on the use of capillary electrophoresis to quantify active constituents (i.e., phenolic compounds, coumarins, protoberberines, curcuminoids, iridoid glycosides, alkaloids, triterpene acids) in medicinal plants and herbal formulations. The present literature review is founded on PRISMA guidelines and selection criteria were formulated on the basis of PICOS (Population, Intervention, Comparison, Outcome, Study type). The scrutiny reveals capillary electrophoresis with ultraviolet detection as the most frequently used capillary electromigration technique for the selective separation and quantification of bioactive compounds. For the purpose of improvement of resolution and sensitivity, other detection methods are used (including mass spectrometry), modifiers to the background electrolyte are introduced and different extraction as well as pre-concentration techniques are employed. In conclusion, capillary electrophoresis is a powerful tool and for given applications it is comparable to high performance liquid chromatography. Short time of execution, high efficiency, versatility in separation modes and low consumption of solvents and sample make capillary electrophoresis an attractive and eco-friendly alternative to more expensive methods for the quality control of drugs or raw plant material without any relevant decrease in sensitivity.     

532nm激光诱导荧光毛细管阵列电泳仪的研制

基于共聚焦激光诱导荧光检测技术,研制了一台旋转扫描高效毛细管阵列电泳装置。以波长为532nm的半导体二极管激光器作为激发光源,多根毛细管阵列采用圆形布局,微型高速直流电机带动旋转反射镜进行激光扫描,加快了数据采集的速度;采用旋转编码器实现了毛细管的定位与位置读出,并触发数据采集系统进行荧光信号采集。以罗丹明6G和罗丹明B为分析样品,考察了16通道毛细管阵列电泳仪的基本性能。     

毛细管电泳多脉冲溶出安培检测方法的研究

 摘要：将用于电化学检测的三电极与驱动电泳分离的电化学系统的接地电极在毛细管出口处的外面作适当的布置,可最大程度地减少高压电场对安培检测的干扰。多阶脉冲溶出安培检测方式提高了电流检测灵敏度,并可在一定程度上通过不同的溶出电位鉴别分离组分。将该方法应用于铜、锌、铅、铊、镉等离子的毛细管电泳分离,得到了较满意的结果。     

532 nm激光诱导荧光毛细管阵列电泳仪的研制

基于共聚焦激光诱导荧光检测技术,研制了一台旋转扫描高效毛细管阵列电泳装置.以波长为532nm的半导体二极管激光器作为激发光源,多根毛细管阵列采用圆形布局,微型高速直流电机带动旋转反射镜进行激光扫描,加快了数据采集的速度;采用旋转编码器实现了毛细管的定位与位置读出,并触发数据采集系统进行荧光信号采集.以罗丹明6G和罗丹明B为分析样品,考察了16通道毛细管阵列电泳仪的基本性能.     

Detection of transferrin isoforms in human serum: comparison of UV and ICP–MS detection after CZE and HPLC separations

Two methods for separation of transferrin (Tf) sialoforms, capillary electrophoresis (CE) and high performance liquid chromatography (HPLC) with conventional UV absorbance detection, have been investigated and compared. First, conditions affecting the separation of the Tf isoforms by capillary zone electrophoresis and HPLC were carefully optimized. The use of 15 mmol L⁻¹ borate buffer (pH 8.4) containing 3 mmol L⁻¹ diaminobutane (DAB) as additive enabled good separation of the Tf isoforms by CE (75 cm×50 μm i.d. fused silica capillary) at 25 kV. In HPLC, a gradient of ammonium acetate (from 0 to 250 mmol L⁻¹ in 45 min) buffered at pH 6 (Tris-HCl) proved suitable for separation of Tf isoforms on a Mono-Q HR 5/5 anion-exchange column. On-line specific detection of the iron associated with the different Tf isoforms, after Fe saturation, by inductively coupled plasma mass spectrometry (ICP–MS) was studied in detail to compare its analytical performance with UV detection. For both CE and HPLC an octapole reaction system (ORS) ICP–MS instrument was used to minimize polyatomic interferences on the ⁵⁶Fe major isotope. Limits of detection of the different isoforms were in the range of 0.02–0.04 μmol L⁻¹ Tf for HPLC–ICP (ORS)–MS. This hybrid technique proved more selective and reliable detection of transferrin isoforms with 2, 3, 4, 5, and 6 sialic acid residues (S₂, S₃, S₄, S₅, and S₆) in real serum samples. Interesting results from iron speciation of Tf in serum from healthy individuals and from pregnant women are given.     

Fast enantiomeric separation with vancomycin as chiral additive by co-electroosmotic flow capillary electrophoresis: increase of the detection sensitivity by the partial filling technique

A fast and sensitive method is described by using vancomycin as a chiral additive for enantiomeric separation by capillary electrophoresis (CE). In order to overcome disadvantages associated with use of vancomycin as chiral additive in CE, several strategies including the dynamic coating technique, the co-electroosmotic flow technique, and the partial filling technique were employed sequentially in this method. Using the polycationic polymer hexadimethrine bromide (HDB) as a buffer additive, the capillary wall was dynamically coated with a thin film formed by the adsorbed HDB. Consequently, the adsorption of vancomycin onto the capillary wall was minimized via electrostatic repulsion between the coating of the capillary wall and the vancomycin molecule. In addition, the reversed electroosmotic flow (from cathode to anode) produced by the positively charged capillary wall migrates in the same direction of negatively charged analytes (co-electroosmotic flow electrophoresis). Thereby the electrophoretic mobility of negatively charged analytes were drastically accelerated leading to a short separation time of less than 3.4 min. The separation time was further reduced by the use of a short-end-injection technique. For example, the analysis time was achieved by as short as 55 s for a baseline separation of dansyl-alpha-amino-n-butyric acid. Concurrently, the partial filling technique was used to avoid the loss of detection sensitivity caused by the presence of vancomycin in the running buffer. The effect of several parameters, such as HDB concentration, buffer pH, plug length of the chiral selector, concentration of the chiral selector and applied voltage, on enantioselectivity were investigated toward optimization. Besides the advantage of a very short separation time, the method is characterized by high detection sensitivity, high selectivity, and high efficiency.     

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.     

Solid-phase microextraction coupled with capillary electrophoresis for the determination of propranolol enantiomers in urine using a sol-gel derived calix[4]arene fiber

A new type of diglycidyloxy-calix[4]arene coated fiber made by sol-gel method was initially prepared for capillary electrophoresis (CE) sample pretreatment. By using headspace solid-phase microextraction (SPME) combined with a novel back-extraction facility coupled off-line to capillary zone electrophoresis (CZE), the simultaneous determination of propranolol enantiomers in human urine was achieved. The clean up effect and preconcentration effect were realized for the first time without derivatization during the SPME process in terms of these strong polarity and thermal stable compounds. Ultrasonic back-extraction and field amplified sample injection (FASI) technologies were employed. Extraction and back-extraction parameters were optimized. Preconcentration of the sample by calix[4]arene fiber based SPME and FASI increased the sensitivity, yielding a limit of detection (LOD) of 0.01microg/ml by CZE-diode array detection (DAD). Method repeatability (RSD<6.5%) and fiber reusability (>150 extraction procedures) were observed over a linear range (0.05-10microg/ml) in urine samples. Based on the superior thermal stability, high alkali- and solvent-resistant ability, marvelous repeatability and long lifetime of the novel fiber, this SPME-FASI-CZE procedure could meet the demand of minimum required performance limit (MRPL) set by the World Anti-doping Agency (WADA) for the detection of propranolol in urine samples.     

The immunoassay of methotrexate by capillary electrophoresis with laser-induced fluorescence detection.

Immunoassay is widely employed as a highly sensitive, specific analytical method for hormones and drugs in biological samples. A technique utilizing capillary electrophoresis with laser-induced fluorescence detection was examined based on the reaction process of these immunoassays in order to develop a protocol characterized by high sensitivity and high speed. The conditions of the antigen-antibody reaction and capillary electrophoresis were variously examined using fluorescein-labeled methotrexate and the antibody of methotrexate. As a result, the immunoassay could be completed within a few minutes. Moreover, detection in the pg range could be accomplished. The sensitivity corresponded to that of radioimmunoassay. A simultaneous multi-component analysis of the immunoassay is also possible due to the high resolving power of capillary electrophoresis. In this study, the possibility of a simultaneous analysis of methotrexate and vancomycin was also investigated.     

Capillary electrophoresis,high‐performance liquid chromatography,and thin‐layer chromatography analyses of phenolic compounds from rapeseed plants and evaluation of their antioxidant activity

Rapeseed plants, known for oil production, are also known to contain phenolic compounds such as phenolic acids and flavonoids, with potential antioxidant and anticancer activities. The separation and identification of 11 phenolic acids in rapeseed extracts (including leaves, flowers, Chinese seeds, Belgian seeds, and cake) by capillary electrophoresis were investigated. The results were compared with those obtained with high‐performance liquid chromatography and thin‐layer chromatography and showed that the capillary electrophoresis technique offers several advantages for the identification of phenolic compounds in various rapeseed extracts. The antioxidant activity of rapeseed extracts and reference compounds was evaluated using four different approaches, namely, 2,2′‐azinobis‐ (3‐ethylbenzohiazoline‐6‐sulfonic acid assay, free radical 2,2‐diphenyl‐1‐picrylhydrazyl assay, electron paramagnetic resonance spectroscopy and the measurement of the total polyphenol content. The contents of total polyphenols in the tested extracts were ranging between 5.4 and 21.1% m/m and ranked as follows: Chinese seeds ? Belgian seeds ? Flowers ? Cake ? Leaves.     

Sensitivity improvement in capillary electrophoresis using organo-aqueous separation buffers and thermal lens detection

It is shown that organo-aqueous separation buffers show much promise when used in capillary electrophoresis separations with photothermal (thermal lens) detection systems. Acetonitrile–water and methanol–water mixtures were selected, as conventionally used in capillary electrophoresis. It is shown that, despite more sophisticated experimental conditions (significant heat outflow from the capillary body) and peak detection, the theoretical ratio of the thermal lens signal for a binary mixture to the thermal lens signal for an aqueous solution (or the corresponding ratio obtained experimentally under bulk batch conditions) can be used to predict the sensitivity of thermal lens detection in capillary electrophoresis. The limits of detection for 2-, 3-, and 4-nitrophenols selected as model compounds in 70% v/v acetonitrile separation buffers are 1×10⁻⁶ M, 1×10⁻⁶ M and 3×10⁻⁷ M, respectively, and are therefore decreased by a factor of six compared to thermal lens detection in aqueous separation buffers. The overall increase in the thermal lens detection sensitivity in a 100% ACN buffer is a factor of 13.      

Fe³⁺-immobilized nanoparticle-modified capillary for capillary electrophoretic separation of phosphoproteins and non-phosphoproteins

A fused-silica capillary modified with Fe3?-immobilized magnetic nanoparticles (Fe3?-IMAN) has been investigated for the capillary electrophoretic (CE) separation of phosphoproteins and non-phosphoproteins. The Fe3?-IMAN capillary was achieved by covalently immobilising epoxy-based magnetic silica nanoparticles (160?nm) on the prederivatized 3-aminopropyl-trimethoxysilane (APTMS) fused-silica capillary (75?μm id), followed by disodium iminodiacetate and Fe3?. The buildup process was examined by measuring the streaming potentials of the bare capillary, APTMS capillary, epoxy-based nanoparticle capillary and Fe3?-IMAN capillary by varying the buffer pH. An inverted fluorescence microscope was used to determine the surface features of the Fe3?-IMAN capillary derivatized with morin. Further experimental results confirmed that Fe3?-IMAN bonded on the inner wall of the APTMS capillary could provide sufficient solute-bonded phase interactions to allow for the CE separation of phosphoproteins and non-phosphoproteins at concentration levels down to 50?μg/mL. The highest number of theoretical plates obtained was about 233,000/m, and the relative standard deviation (RSD) for migration times was <2.57% for eight consecutive runs, respectively. Additionally, the Fe3?-IMAN modifing method was also applied to the analyses of bovine milk proteins. With simplicity, high resolving power, and high repeatability, the proposed method has shown great potential for phosphoproteomics applications.     

Capillary liquid chromatography-mass spectrometry and micellar electrokinetic chromatography as complementary techniques in environmental analysis

Applications of capillary electrophoresis (CE) and capillary liquid chromatography (LC) to environmental analysis have been limited. In this work we present applications of micellar electrokinetic chromatography (MEKC) to the analysis of environmental matrices for synthetic dyes. Separations obtained by capillary LC are compared with those obtained under MEKC for seven selected dyes. Both techniques are capable of resolving the subject compounds at high efficiency. Recovery data for spiked water and soil matrices were obtained for four dyes using solid-phase extraction cartridges and disks with determination by MEKC-UV detection. Both pH adjustment via acid and ion-pairing via a cationic surfactant were investigated for isolating dyes. Capillary LC detection was by continuous-flow liquid secondary ion mass spectrometry (CF-LSI-MS) whereas MEKC used UV detection (214 nm). Application of peak-profiling at high mass resolution is illustrated with the capillary LC-MS technique. Interfacing capillary LC under CF-LSI-MS using the coaxial arrangement is easier than interfacing CE with this arrangement. MEKC provides a powerful screening and determinative technique, while capillary LC-MS provides a confirmatory tool.     

Applications of capillary electrophoresis with electrochemical detection in pharmaceutical and biomedical analyses

As a high efficiency separation technique, capillary electrophoresis has been widely used in various fields of analytical science. This review discusses the applications of electrochemical detection systems combined with capillary electrophoresis in pharmaceutical and biomedical analysis. These detection methods mainly involve amperometric detection but also include conductivity detection and potentiometric detection. Its applications in the field are divided into six parts, including catechol compounds, thiols, amino acids and peptides, carbohydrates, general pharmaceuticals, and other related compounds. A relatively detailed discussion is described for each compound under the current studied. On this basis, we have suggested several conceivable directions for capillary electrophoresis with electrochemical detection in the future.     

Enhancing Detection Sensitivity in Capillary Electrophoresis

A simple technique was proposed for improving detection sensitivity in capillary electrophoresis by the chemical etching of the interior surface of a fused-silica capillary in the detection region. This technique was applied to the electrophoresis of proteins. The sensitivity was found to increase, on the average, by a factor of 4 to 5 after etching a 75-m i.d. capillary with an HF solution for 7 min.     

Development of an on-column enrichment technique based on C18-functionalized magnetic silica nanoparticles for the determination of lidocaine in rat plasma by high performance liquid chromatography

In this study, a novel on-column enrichment technique filled with C(18)-functionalized magnetic silica nanoparticles was successfully developed for the determination of lidocaine in rat plasma by high performance liquid chromatography (HPLC). The synthesized Fe(3)O(4)@SiO(2)-C(18) nanoparticles were locally packed into the capillary by the application of magnets. Lidocaine in the sample solutions pumped into the capillary tube could be easily adsorbed by Fe(3)O(4)@SiO(2)-C(18) through hydrophobic interaction by the interior C(18) groups, and eluted by acetonitrile solution. Different extraction conditions were investigated. Method validations including linear range, quantification limit, detection limit, precision, accuracy and recovery were also studied. The results showed that the proposed method based on on-column enrichment by Fe(3)O(4)@SiO(2)-C(18) was a novel, little solvent and efficient approach for the determination of lidocaine in the complex plasma samples.