Recent advances in amino acid analysis by capillary electrophoresis

Preparation of Flower-like Nanosilver Based on Bioderived Caffeic Acid for Raman Enhancement and Dye Degradation

In this study, a simple, green, and low-cost room temperature synthesis of broccoli-like silver nanoflowers (AgNF) with a particle size of about 300-500 nm was developed using plant-derived caffeic acid as a reducing agent and polyvinylpyrrolidone as a dispersant under ultrasound assistance. The flower clusters covered by small nanocrystals of 20-50 nm significantly enhance the electromagnetic field signals. AgNF was deposited on the surface of silicon wafers as a surface-enhanced Raman spectroscopy sensor for the detection of probe molecules such as rhodamine 6G (R6G) and malachite green with high sensitivity, homogeneity, and reproducibility. AgNF was deposited on cotton fabrics in the form of composites to catalyze the degradation of dye pollutants such as R6G, MG, and methyl orange in the presence of sodium borohydride. 0.1 g of AgNF/cotton fabric could assist 15 mmol/L NaBH4 to achieve over 90% degradation of various dyes as well as a high concentration of dyes in 12 min with good reusability and recyclability. The AgNF synthesized in this work can not only monitor the type and amounts of pollutants (dyes) in wastewater but also catalyze the rapid degradation of dyes, which is expected to be valuable for industrial applications.

Absolute quantitative analysis of endogenous neurotransmitters and amino acids by liquid chromatography-tandem mass spectrometry combined with multidimensional adsorption and collision energy defect

Considering that neurotransmitters (NTs) and amino acids (AAs) exert pivotal roles in various neurological diseases, global detection of these endogenous metabolites is of great significance for the treatment of nervous system diseases. Herein, a workflow that could cope with various challenges was proposed to establish an extendable all-in-one injection liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay for analyzing these small molecular metabolites with high coverage. To obtain a qualified blank biological matrix for the preparation of standard curves and quality control samples, different absorption solvents, including activated carbon (AC), calcite (Cal) and montmorillonite (Mnt) were systematically evaluated for efficient absorption of endogenous substances with minimum residue. We also firstly proposed a "Collision Energy Defect (CED)" strategy to solve the huge difference of mass signal strength caused by different properties and concentrations of 11 NTs and 17 AAs. The quantitative results were validated by LC-MS/MS. Sensitivity, accuracy, and recovery meeting generally accepted bioanalytic guidelines were observed in a concentration span of at least 100 to 500 times for each analyte. Then the temporal changes of intracerebral and peripheral NTs and AAs in ischemic stroke model and sham operated rats were successfully produced and compared using the described method. All these results suggested that the currently developed assay was powerful enough to simultaneously monitor a large panel of endogenous small molecule metabolites, which was expected to be widely used in the research of various diseases mediated by NTs and AAs.

CE-UV for the characterization of passion fruit juices provenance by amino acids profile with the aid of chemometric tools

A separation method was developed in order to quantify free amino acids in passion fruit juices using CE-UV. A selective derivatization reaction with FMOC followed by MEKC analysis was chosen due to the highly interconnected mobilities of the analytes, enabling the separation of 22 amino acids by lipophilicity differences, as will be further discussed. To achieve such results, the method was optimized concerning BGE composition (concentrations, pH, and addition of organic modifier) and running conditions (temperature and applied voltage). The optimized running conditions were: a BGE composed by 60 mmol/L borate buffer at pH 10.1, 30 mmol/L SDS and 5 % methanol; running for 40 min at 23°C and 25 kV. The method was validated and applied on eight brands plus one fresh natural juice, detecting 12 amino acids. Quantification of six analytes combined with principal component analysis was capable to characterize different types of juices and showed potential to detect adulteration on industrial juices. Glutamic acid was found to be the most concentrated amino acid in all juices, exceeding 1 g/L in all samples and was also crucial for the correct classification of a natural juice, which presented a concentration of 22 g/L.

A dispersive liquid-liquid microextraction and chiral separation of carvedilol in human plasma using capillary electrophoresis

BACKGROUND

Development of simple, rapid and precise analysis of chiral drugs in biological samples is an important issue. Dispersive liquid-liquid microextraction in combination with CE using field amplified sample injection has been of interest because of its capability to analyze trace amount of drugs.

METHODS

Dispersive liquid-liquid microextraction-CE-field amplified sample injection was employed for chiral separation of carvedilol in human plasma using UV-DAD detector and the developed method has been validated according to US FDA method validation guideline for bioanalysis.

RESULTS

The method was linear over a concentration range of 12.5-100 ng/ml for each carvedilol enantiomer (R(2) = 0.998) and the mean recoveries ranged from 91 to 107%.

CONCLUSION

The method was adapted for sensitive, selective and rapid determination of carvedilol enantiomers in human plasma samples.

Baseline separation of amino acid biomarkers of hepatocellular carcinoma by polyvinylpyrrolidone-filled capillary electrophoresis with light-emitting diode-induced fluorescence in the presence of mixed micelles

Separation of amino acid biomarkers could be performed by polyvinylpyrrolidone-filled capillary electrophoresis in the presence of mixed micelles.

Chiral derivatizations applied for the separation of unusual amino acid enantiomers by liquid chromatography and related techniques

Amino acids are essential for life, and have many functions in metabolism. One particularly important function is to serve as the building blocks of peptides and proteins, giving rise complex three dimensional structures through disulfide bonds or crosslinked amino acids. Peptides are frequently cyclic and contain proteinogenic as well as nonproteinogenic amino acids in many instances. Since most of the proteinogenic α-amino acids contain at least one stereogenic center (with the exception of glycine), the stereoisomers of all these amino acids and the peptides in which they are to be found may possess differences in biological activity in living systems. The impetus for advances in chiral separation has been highest in the past 25 years and this still continues to be an area of high focus. The important analytical task of the separation of isomers is achieved mainly by chromatographic and electrophoretic methods. This paper reviews indirect separation approaches, i.e. derivatization reactions aimed at creating the basis for the chromatographic resolution of biologically and pharmaceutically important enantiomers of unusual amino acids and related compounds, with emphasis on the literature published from 1980s. The main aspects of the chiral derivatization of amino acids are discussed, i.e. derivatization on the amino group, transforming the molecules into covalently bonded diastereomeric derivatives through the use of homochiral derivatizing agents. The diastereomers formed (amides, urethanes, urea and thiourea derivatives, etc.) can be separated on achiral stationary phases. The applications are considered, and in some cases different derivatizing agents for the resolution of complex mixtures of proteinogenic d,l-amino acids, non-proteinogenic amino acids and peptides/amino acids from peptide syntheses or microorganisms are compared.

Recent advances in amino acid analysis by capillary electrophoresis

This paper describes the most important articles that have been published on amino acid analysis using CE during the period from June 2009 to May 2011 and follows the format of the previous articles of Smith (Electrophoresis 1999, 20, 3078-3083), Prata et al. (Electrophoresis 2001, 22, 4129-4138) and Poinsot et al. (Electrophoresis 2003, 24, 4047-4062; Electrophoresis 2006, 27, 176-194; Electrophoresis 2008, 29, 207-223; Electrophoresis 2010, 31, 105-121). We present new developments in amino acid analysis with CE, which are reported describing the use of lasers or light emitting diodes for fluorescence detection, conductimetry electrochemiluminescence detectors, mass spectrometry applications, and lab-on-a-chip applications using CE. In addition, we describe articles concerning clinical studies and neurochemical applications of these techniques.

Determination of stimulants and narcotics as well as their in vitro metabolites by online CE-ESI-MS

A simple, rapid and sensitive CE-ESI-MS method for the simultaneous analysis of seven stimulants and narcotics (amphetamine, ephedrine, methadone, pethidine, tetracaine, codeine and heroin) was developed. The CE-ESI-MS experimental conditions were optimized as follows: 20 mmol/L ammonium acetate with pH 9.0 as running buffer, the separation voltage of 22 kV and the sheath liquid of isopropanol/water (1:1 v/v) containing 7.5 mmol/L acetic acid with 3.0 μL/min flow rate. Under the optimized conditions, the stimulants and narcotics were well separated within 4.6 min using a 70-cm length fused-silica capillary (50 μm id). The detection limits (S/N=3) of the CE-ESI-MS analysis were in the range of 0.40-1.0 ng/mL. Method repeatability of intra-day and inter-day was satisfactory. The recoveries obtained from the analysis of spiked urine samples were between 84.1 and 108%. The developed method was successfully applied for the simultaneous analysis of methadone, pethidine and codeine and their in vitro metabolites.

Capillary electrophoresis-mass spectrometry for the analysis of amino acids

In this review, the recent contribution of CE-MS technology to the analysis of amino acids, as well as the advantages of the hyphenation and the technologies involved in the instrumental coupling are reported. Different sections are dedicated to the recent contributions of CE-MS to the analysis of protein amino acids and their post-translational modifications, such as phosphorylation and sulfation. CE-MS analysis of some amino acid derivatives, such as the free methylated-derivatives of arginine is also discussed. A section is specifically devoted to the CE-MS applications in the field of chiral separation of D- and L-amino acid enantiomers.

Quantification of neurotransmitter amino acids by capillary electrophoresis laser-induced fluorescence detection in biological fluids

The role of neurotransmitter amino acids (NAAs) in the functioning of the nervous system has been the focus of increasingly intense research over the past several years. Among the various amino acids that have important roles as neurotransmitters, there are alanine (Ala), glutamic acid (Glu), aspartic acid (Asp), serine (Ser), taurine (Tau) and glycine (Gly). NAAs are present in plasma, cells and--at trace levels--in all biological fluids, but complex components in biological matrices make it difficult to determine them in biological samples. We describe a new capillary electrophoresis (CE) method with laser-induced fluorescence detection by which analytes are resolved in less than 12 minutes in a 18 mmol/L phosphate run buffer at pH 11.6. The use of elevated temperatures during sample derivatization leads to a drastic reduction in the reaction time, down to 20 min, compared to the 6-14 h usually described for reactions between FITC and amino acids at room temperature. In order to demonstrate its wide range of applications, the method was applied to the analysis of NAA in human plasma and in other sample types, such as red blood cells, urine, cultured cells, cerebrospinal fluid, saliva and vitreous humor, thus avoiding the typical limitations of other methods, which are normally suitable for use with only one or two matrix types.

Sensitive and rapid method for amino acid quantitation in malaria biological samples using AccQ.Tag ultra performance liquid chromatography-electrospray ionization-MS/MS with multiple reaction monitoring

An AccQ*Tag ultra performance liquid chromatography-electrospray ionization-tandem mass spectrometry (AccQ*Tag-UPLC-ESI-MS/MS) method for fast, reproducible, and sensitive amino acid quantitation in biological samples, particularly, the malaria parasite Plasmodium falciparum is presented. The Waters Acquity TQD UPLC/MS system equipped with a photodiode array (PDA) detector was used for amino acid separation and detection. The method was developed and validated using amino acid standard mixtures containing acidic, neutral, and basic amino acids. For MS analysis, the optimum cone voltage implemented, based on direct infusion analysis of a few selected AccQ*Tag amino acids with multiple reaction monitoring, varied from 29 to 39 V, whereas the collision energy varied from 15 to 35 V. Calibration curves were built using both internal and external standardization. Typically, a linear response for all amino acids was observed at concentration ranges of 3 x 10(-3)-25 pmol/muL. For some amino acids, concentration limits of detection were as low as 1.65 fmol. The coefficients of variation for retention times were within the range of 0.08-1.08%. The coefficients of variation for amino acid quantitation, determined from triplicate UPLC-MS/MS runs, were below 8% on the average. The developed AccQ*Tag-UPLC-ESI-MS/MS method revealed good technical and biological reproducibility when applied to P. falciparum and human red blood cells samples. This study should provide a valuable insight into the performance of UPLC-ESI-MS/MS for amino acid quantitation using AccQ*Tag derivatization.

Electrophoretic migration of proteins in semidilute polymer solutions

We present a systematic study of the electrophoretic migration of 10-200 kDa protein fragments in dilute-polymer solutions using microfluidic chips. The electrophoretic mobility and dispersion of protein samples were measured in a series of monodisperse polydimethylacrylamide (PDMA) polymers of different molecular masses (243, 443, and 764 kDa, polydispersivity index <2) of varying concentration. The polymer solutions were characterized using rheometry. Prior to loading onto the microchip, the polymer solution was mixed with known concentrations of SDS (SDS) surfactant and a staining dye. SDS-denatured protein samples were electrokinetically injected, separated, and detected in the microchip using electric fields ranging from 100 to 300 V/cm. Our results show that the electrophoretic mobility of protein fragments decreases exponentially with the concentration c of the polymer solution. The mobility was found to decrease logarithmically with the molecular weight of the protein fragment. In addition, the mobility was found to be independent of the electric field in the separation channel. The dispersion is relatively independent of polymer concentration and it first increases with protein size and then decreases with a maximum at about 45 kDa. The resolution power of the device decreases with concentration of the PDMA solution but it is always better than 10% of the protein size. The protein migration does not seem to correspond to the Ogston or the reptation models. A semiempirical expression for mobility given by van Winkle fits the data very well.

Recent developments in CE and CEC of peptides

The article brings a comprehensive survey of recent developments and applications of high-performance capillary electromigration methods, zone electrophoresis, ITP, IEF, affinity electrophoresis, EKC, and electrochromatography, to analysis, preparation, and physicochemical characterization of peptides. New approaches to the theoretical description and experimental verification of electromigration behavior of peptides and to methodology of their separations, such as sample preparation, adsorption suppression, and detection, are presented. Novel developments in individual CE and CEC modes are shown and several types of their applications to peptide analysis are presented: conventional qualitative and quantitative analysis, purity control, determination in biomatrices, monitoring of chemical and enzymatical reactions and physical changes, amino acid and sequence analysis, and peptide mapping of proteins. Some examples of micropreparative peptide separations are given and capabilities of CE and CEC techniques to provide important physicochemical characteristics of peptides are demonstrated.

Chiral separation of dansyl amino acids in capillary electrophoresis using mono-(3-methyl-imidazolium)-beta-cyclodextrin chloride as selector

Enantioseparations of fourteen dansyl amino acids were achieved by using a positively-charged single-isomer beta-cyclodextrin, mono-(3-methyl-imidazolium)-beta-cyclodextrin chloride, as a chiral selector. Separation parameters such as buffer pH, selector concentration, separation temperature, and organic modifier were investigated for the enantioseparation in order to achieve the maximum possible resolution. Chiral separation of dansyl amino acids was found to be highly dependent on pH since the degree of protonation of these amino acids can alter the strength of electrostatic interaction and/or inclusion complexation between each enantiomer and chiral selector. In general, the chiral resolution of dansyl amino acids was enhanced at higher pH, which indicates that the carboxylate group on the analytes may interact with the imidazolium group of cationic cyclodextrin. For most analytes, a distinct maximum in enantioresolution was obtained at pH 8.0. Moreover, the chiral separation can be further improved by careful tuning of the separation parameters such as higher selector concentration (e.g. 10 mM), lower temperature, and addition of methanol. Enantioseparation of a standard mixture of these dansyl amino acids was further achieved in a single run within 30 min.

Microfluidics in amino acid analysis

Microfluidic devices have been widely used to derivatize, separate, and detect amino acids employing many different strategies. Virtually zero-dead volume interconnections and fast mass transfer in small volume microchannels enable dramatic increases in on-chip derivatization reaction speed, while only minute amounts of sample and reagent are needed. Due to short channel path, fast subsecond separations can be carried out. With sophisticated miniaturized detectors, the whole analytical process can be integrated on one platform. This article reviews developments of lab-on-chip technology in amino acid analysis, it shows important design features such as sample preconcentration, precolumn and postcolumn amino acid derivatization, and unlabeled and labeled amino acid detection with focus on advanced designs. The review also describes important biomedical and space exploration applications of amino acid analysis on microfluidic devices.

Amino acids: Aspects of impurity profiling by means of CE

Quality control of active pharmaceutical ingredients (API) is commonly performed by means of HPLC. However, CE offers a suitable alternative, especially for the analysis of easily chargeable substances, i.e., amino acids. The article reviews, on the one hand, CE methods developed for impurity profiling of synthesized amino acid analogs. However, nowadays, production of amino acids/peptides is dominated by fermentation. Therefore, on the other hand, CE methods for the analysis of amino acids and small peptides are reported. The results of CE analysis of glutathione samples according to the monograph in the European Pharmacopoeia (Ph. Eur.) 5.7 and amino acid samples after derivatization with 9-fluorenylmethyl chloroformate (FMOC) and 3-(4-carboxybenzoyl)quinoline-2-carboxaldehyde (CBQCA) may pave the way for impurity profiling of fermentatively produced API by means of CE.

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).