Determination of tea catechins

An overview of analytical methods for the measurement of biologically important tea catechins is presented. Liquid chromatography and capillary electrophoresis are the most cited techniques for catechin separation, identification and quantitation. Liquid chromatography with ultraviolet detection is frequently used; however, mass spectrometry, electrochemical, fluorescence and chemiluminescence detection are also utilized in cases where more sensitive or selective detection is needed. Two modes of capillary electrophoresis, capillary zone electrophoresis and micellar electrokinetic capillary chromatography, have been employed for the determination of catechins. Both modes of capillary electrophoresis are based on ultraviolet detection. Additional analytical techniques, such as gas chromatography, thin-layer chromatography, paper chromatography, spectrophotometry, biosensing, chemiluminescence and nuclear magnetic resonance spectroscopy have also been utilized for the determination of catechins and are reviewed herein.     

Screening method for detecting cross-contamination residues of tiamulin in swine feeds

A method was developed for the determination of tiamulin (TML), 14-deoxy-14-[(2-diethylaminoethyl)mercaptoacetoxy]mutilin hydrogen fumarate, a semisynthetic derivative of the naturally occurring antibiotic pleuromutilin produced by the fungus Pleurotus mutilis. This drug, with high activity against Gram-positive bacteria, some Gram-negative bacteria, and several strains of mycoplasms is administered to animals in food, drinking water, or by injection; however, its chemical structure causes problems in analysis of feeds. Although the molecule is charged below pH 8, attempts to analyze TML-containing extracts on ion-exchange columns or other polar stationary phases have failed. Additionally, TML shows no fluorescence activity and only poor UV activity. The present method consists of organic solvent extraction followed by liquid chromatography with UV detection. A low wavelength (208 nm) was used for detection. Limits of detection and quantitation, as well as data for recovery and repeatability obtained during characterization of the method, are described. The applicability of the optimized method was tested by analyzing commercial blank feeds processed after TML-medicated feeds.     

Capillary supercritical fluid chromatography with ultraviolet multichannel detection of some pesticides and herbicides

The useful combination of capillary supercritical fluid chromatography with ultraviolet multichannel detection is demonstrated by the analysis of selected pesticides and herbicides. In this application the advantages of compound identification by ultraviolet spectrometry are appended to the separating capability of capillary supercritical fluid chromatography. A pseudo oncolumn detection approach is used. Compromises from the theoretically ideal conditions for both capillary SFC and the multichannel UV detector are made to achieve a practical interfacing of the chromatographic and spectrophotometric techniques. Detection limits are at the low nanogram levels.     

Hyphenated chromatographic methods for biomaterials

The improvement in hyphenated analytical techniques has significantly widened their applications to the analysis of biomaterials. In this article, we discuss recent advances in applications of hyphenated chromatographic techniques including capillary electrophoresis to the analyses of biological samples. As tools of separation, gas chromatography, high-performance liquid chromatography and capillary electrophoresis are considered with special emphasis on applications utilizing the hyphenation of these methods to mass spectrometry. Moreover, applications using other detection methods such as Fourier transform infrared spectroscopy hyphenated to gas chromatography and photodiode array detector combined with high-performance liquid chromatography or capillary electrophoresis are also discussed. Owing to their high sensitivity, luminescence-based detection systems such as laser-induced fluorescence and chemiluminescence are also included in this review.     

The role of liquid chromatography in proteomics

Proteomics represents a significant challenge to separation scientists because of the diversity and complexity of proteins and peptides present in biological systems. Mass spectrometry as the central enabling technology in proteomics allows detection and identification of thousands of proteins and peptides in a single experiment. Liquid chromatography is recognized as an indispensable tool in proteomics research since it provides high-speed, high-resolution and high-sensitivity separation of macromolecules. In addition, the unique features of chromatography enable the detection of low-abundance species such as post-translationally modified proteins. Components such as phosphorylated proteins are often present in complex mixtures at vanishingly small concentrations. New chromatographic methods are needed to solve these analytical challenges, which are clearly formidable, but not insurmountable. This review covers recent advances in liquid chromatography, as it has impacted the area of proteomics. The future prospects for emerging chromatographic technologies such as monolithic capillary columns, high temperature chromatography and capillary electrochromatography are discussed.     

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.     

Separation of chlorins and carotenoids in capillary electrophoresis

The present study reports the investigation of capillary electrophoresis (CE) for the separation of the photosynthetic pigments (chlorophyll derivatives as well as carotenoids) together. Various CE methods, such as micellar electrokinetic chromatography, capillary electrokinetic chromatography, and nonaqueous capillary electrophoresis (NACE) are tested, with coated and uncoated capillary columns to evaluate optimal separation conditions using diode array detection. The effect of different type and composition of organic solvents and surfactants on the separation is discussed. Detection limits are found in the range of 1.14-2.45 ppm. According to the system suitability results, the most effective separation is observed using NACE with Aliquat 336 as cationic surfactant in coated capillary and mixture of MeOH-ACN-THF (5:4:1, v/v/v) as solvent. Quantitative evolution is investigated, and recovery percentage values are found to be 96.7-102%.     

Determination of carnosine in feed and meat by high-performance anion-exchange chromatography with integrated pulsed amperometric detection

Carnosine (beta-alanyl-L-histidine) is a dipeptide regarded as an important molecular marker of the presence of processed animal proteins including meat and bone meal in animal feed. For its identification and quantification a sensitive and selective method by high-performance anion-exchange chromatography coupled with integrated pulsed amperometric detection (HPAEC-IPAD) was developed. The assay is based on isocratic elution with 100 mM NaOH as the mobile phase. Interferences of real matrices were efficiently removed; carnosine could be determined at the concentration ranges 0.1-100 microM with a rather low detection limit of 0.23 ng. Unlike feeds for dogs and cats, no carnosine peak was observed in all examined feeds for ruminants. The good analytical characteristics allowed camosine determination down to 5 microg/g of feed.     

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.     

Study on open tubular capillary affinity liquid chromatography

A novel mode of affinity chromatography (AC) based on an open tubular capillary column (OTAC) is demonstrated. The OTAC column is prepared by immobilizing Cibacron blue F3GA onto the inner surface of a 50-microm-i.d. capillary column. The AC experiment is performed on a capillary electrophoresis instrument by using its pressure system as the driving force. Bovine serum albumin and lysozyme (Lys) are successfully separated with stepwise gradient elution. The relative standard deviation (RSD) for the elution time of the retained Lys is 0.08%, and good repeatability of its peak area and peak height with an RSD value lower than 2.12% for 10 consecutive runs is observed. The loading capacity and detection limit for the retained Lys are approximately 36 ng and 8.6 ng, respectively. It is also found that the amount of protein adsorbed is unaffected by the flow rate of the loading buffer, and OTAC can be used for the fast determination of biopolymers. Some of the advantages of OTAC over conventional modes of open tubular capillary liquid chromatography are that the detection sensitivity and loading capacity of a sample can be greatly improved, because the relatively large inner diameter of the capillary can be adopted and the whole capillary column can be used to adsorb the solute in OTAC.     

Electroosmotic pump‐supported molecularly imprinted monolithic column for capillary chromatographic separation of nitrophenol isomers

In this work, a novel molecularly imprinted polymer (MIP) monolithic column with integrated in‐column electroosmotic pump (EOP) was designed and successfully prepared to facilitate the capillary chromatography with MIP column. A silica‐based EOP was synthesized at the detection end of the MIP monolithic capillary column by so‐gel to provide the hydrodynamic driven force for the capillary chromatography. Because of large surface area and low fluidic resistance of the silica monolith,a strong and steady EOF was generated by silica‐based EOP, indicating that the EOP was quite compatible with MIP capillary column. With the sufficient EOF provided by EOP, the electro‐driven based capillary chromatographic separation of nitrophenol isomers was achieved in 4‐vinylpyridine‐based MIP monolithic capillary, which was originally proved infeasible because of the EOF shortage. No significant influence upon the specific recognition of the MIP was found due to the setting of EOP after the detection window of the column. The influence of experimental parameters on the EOF such as voltage and pH value of running buffer was investigated. The column was also evaluated by capillary liquid chromatographic mode to compare with EOP‐driven capillary chromatography. Higher column efficiency was obtained by EOP‐driven separation with improved peak shape. The results suggested that EOP‐supported technique would be a good way to solve the problem of weak EOF generation in electro‐driven capillary chromatography.     

Comparison between transient isotachophoretic capillary zone electrophoresis and reversed-phase liquid chromatography for the determination of peptides in plasma.

Low levels of peptide drugs in human plasma can be determined employing off-line solid-phase extraction, followed by capillary zone electrophoresis with UV detection. A bioanalytical procedure is presented, using gonadorelin and angiotensin II in human plasma as model compounds. The solid-phase extraction method, based on a weak cation exchange mechanism, is able to remove interfering endogenous components from the plasma sample, extract the model peptides quantitatively, and give a possibility of concentrating the sample at the same time. Transient isotachophoretic conditions were kept to increase the sample loadability by about two orders of magnitude. Up to about 70% of the capillary was filled with the reconstituted extract, whereafter the peptides were selectively concentrated during the first 15 min. Subsequently, the concentrated sample zones were separated under capillary zone electrophoresis conditions, showing the technique's high resolution. For the model cationic peptides (gonadorelin, angiotensin II) good linearity and reproducibility was observed in the 20-100 ng/mL concentration range. A more extensive washing procedure permits quantitation of gonadorelin at the 5 ng/mL level. In comparison with a liquid chromatography analysis, superior mass sensitivity and separation are obtained with the transient isotachophoretic capillary zone electrophoresis method. Moreover, in this case equivalent sensitivity is achieved when it is directly compared with a liquid chromatography method with UV detection, keeping in mind that 60 times more sample is needed for the latter method. A further gain in sensitivity can be obtained when the analysis is combined with native fluorescence detection, as is demonstrated by combining liquid chromatography separation with fluorescence detection.     

Rapid determination of the critical micelle concentration by Taylor dispersion analysis in capillaries using both direct and indirect detection

The critical micelle concentration is a basic characteristic of surfactants. In this article, the process of formation of micelles is studied by Taylor dispersion analysis using capillary electrophoresis instrumentation as a substituent of capillary liquid chromatography. New methods for determination of critical micelle concentration are presented. Sodium octylbenzene sulfonate and sodium dodecylsulfate are used as model compounds with and without chromophore. Two novel approaches based on indirect ultraviolet detection and indirect Taylor dispersion analysis with direct ultraviolet detection are introduced for the determination of critical micelle concentration value of surfactant without any chromophore. The determined critical micelle concentration values are in correspondence with the tabulated values at 95% confidence level.     

Simultaneous determination of 10 first-generation histamine h1 receptor blockers in feeds by ultra-high-performance liquid chromatography triple quadrupole ion trap hybrid mass spectrometer

A method for simultaneous determination of 10 first-generation histamine H1 receptor blockers in feeds by ultra-high-performance liquid chromatography triple quadrupole mass spectrometry combined with solid phase extraction. Instrument conditions, extraction solvents, and purification methods have been optimized. Under the optimum conditions, these analytes were separated effectively at 6 min. These feeds have been extracted by acid acetonitrile and purified by mixed cation exchange solid-phase extraction. The performance of this method meets the requirements of veterinary residue detection in feeds in China. It is appropriate for the confirmatory monitoring and quantitative analysis of 105 feed samples, five kinds of histamine H1 receptor blockers have been detected in 10 samples.     

On-line preconcentration methods for capillary electrophoresis

The limits of detection (LOD) for capillary electrophoresis (CE) are constrained by the dimensions of the capillary. For example, the small volume of the capillary limits the total volume of sample that can be injected into the capillary. In addition, the reduced pathlength hinders common optical detection methods such as UV detection. Many different techniques have been developed to improve the LOD for CE. In general these techniques are designed to compress analyte bands within the capillary, thereby increasing the volume of sample that can be injected without loss of CE efficiency. This on-line sample preconcentration, generally referred to as stacking, is based on either the manipulation of differences in the electrophoretic mobility of analytes at the boundary of two buffers with differing resistivities or the partitioning of analytes into a stationary or pseudostationary phase. This article will discuss a number of different techniques, including field-amplified sample stacking, large-volume sample stacking, pH-mediated sample stacking, on-column isotachophoresis, chromatographic preconcentration, sample stacking for micellar electrokinetic chromatography, and sweeping.     

Analysis of anions in aqueous samples by ion chromatography and capillary electrophoresis. A comparative study of peak modeling and validation criteria.

The object of this study is the comparison of two methods for the quantitative analysis of anions in aqueous samples: ion chromatography with conductimetric detection, and capillary zone electrophoresis with indirect photometric detection. The comparison includes modeling of experimental peaks as well as statistical validation criteria according to the recommendations of the International Conference on Harmonisation. In ion chromatography, peak shapes are Gaussian or exponentially modified Gaussian, and the number of theoretical plates calculated using the appropriate mathematical relations correspond well to those obtained from statistical moments. Peaks in capillary electrophoresis, however, do not follow the same models. A different model, treating the peaks as right angle triangles, has been studied. Equations corresponding to this model permit a good estimation of plate numbers. The statistical validation of these methods includes detection limits, linearity, accuracy and precision. Overall, ion chromatography yields better validation results than capillary electrophoresis. In the latter method the injection mode plays an important role, with voltage injection giving lower detection limits than hydrodynamic injection.     

生物样品中儿茶酚胺类物质分析方法的研究进展

儿茶酚胺是人体内重要的神经递质,血浆及尿中儿茶酚胺的浓度水平可用于诊断高血压、嗜铬细胞瘤及成神经细胞瘤等病症,因而准确测定人体生物样品中儿茶酚胺类物质代谢浓度的变化,在疾病的诊断和治疗中具有重要的意义。该文综述了人体液和组织中儿茶酚胺类物质的不同分析方法,包括高效液相色谱法、毛细管电泳法、质谱法、电化学法、化学发光法、荧光光度法等。     

Review. Use of laser detectors in capillary liquid chromatography

The main relationship of high-performance liquid chromatography (HPLC) are considered. It is shown that the optimum conditions of ultrasensitive trace analysis should be achieved by using packed capillary columns manufactured from flexible quartz capillaries with dc approximately less than 0.2 mm. The main features of these columns (v opt = 0.6 v opt of that for conventional HPLC columns with double the hydraulic permeability) make it possible to obtain two or three times higher plate numbers for the same analysis time and column pressure characteristic of conventional HPLC, as a result of using a submicrometre sorbent. The main features of laser detection in capillary liquid chromatography (laser-induced fluorescence and cross-beam thermal lens absorption detectors) are considered. The requirements that should be met by a modern capillary liquid chromatograph based on using flexible quartz capillary columns with a submicrometre sorbent and laser detectors are formulated. Examples of using these systems for femtomole and attomole analyses of biological samples (amino acids and prostaglandins) are given.     

Capillary Electrochromatography of Pyrimidine Derivatives Using UV and Mass Spectrometric Detection

 The separation of pyrimidine derivatives by capillary electrochromatography (CEC) using either UV or mass spectrometric detection is described. For UV detection an aqueous phosphate carrier electrolyte containing acetonitrile is employed. The results are compared to the analysis of the same compounds by micellar electrokinetic chromatography in terms of selectivity, migration times, linearity, and detection limits. For the combination of CEC and mass spectrometry (MS) an inexpensive way to couple commercially available instruments is presented; the interface consists of an electrically grounded stainless steel connector (containing a stainless steel frit) serving as the electrode and coupling the CEC capillary with a fused silica transfer capillary to the MS instrument. Alternatively, a PEEK adapter combining the CEC capillary and a grounded stainless steel transfer capillary serving as the electrode is employed. To avoid the formation of hydrogen gas at the coupling piece or the transfer capillary, p-benzoquinone is added to the carrier electrolyte consisting of aqueous ammonium acetate and acetonitrile.     

High performance stationary phases for planar chromatography

The kinetic performance of stabilized particle layers, particle membranes, and thin films for thin-layer chromatography is reviewed with a focus on how layer characteristics and experimental conditions affect the observed plate height. Forced flow and pressurized planar electrochromatography are identified as the best candidates to overcome the limited performance achieved by capillary flow for stabilized particle layers. For conventional and high performance plates band broadening is dominated by molecular diffusion at low mobile phase velocities typical of capillary flow systems and by mass transfer with a significant contribution from flow anisotropy at higher flow rates typical of forced flow systems. There are few possible changes to the structure of stabilized particle layers that would significantly improve their performance for capillary flow systems while for forced flow a number of avenues for further study are identified. New media for ultra thin-layer chromatography shows encouraging possibilities for miniaturized high performance systems but the realization of their true performance requires improvements in instrumentation for sample application and detection.