Indirect Enantioseparation of Amino Acids by CE Using Automated In-Capillary Derivatization with ortho-Phthalaldehyde and N-Acetyl-l-Cysteine

Determination of amino acids and peptides without their pre-column derivatization by capillary electrophoresis with ultraviolet and contactless conductivity detection. An overview

This review provides an overview of recent works focusing on the determination of amino acids (AAs) and peptides using capillary electrophoresis with contactless conductivity detection and ultraviolet (UV) detection, which is the most widespread detection in capillary electromigration techniques, without pre-capillary derivatization. Available options for the UV detection of these analytes, such as indirect detection, complexation with transition metal ions, and in-capillary derivatization are described. Developments in the field of direct detection of UV-absorbing AAs and peptides as well as progress in chiral separation are described. A separate section is dedicated to using on-line sample preconcentration methods combined with capillary electrophoresis-UV.

Enantioselective HPLC of aryl-substituted oxazolines as an efficient tool for determination of chiral purity of serine medicinal components

A new approach for evaluation of chiral purity of serine esterification products bearing long-chain alkyl substituents was developed. The compounds were simply converted to aryl-substituted oxazolines which: (i) facilitates effective chromatographic enantioseparation and (ii) enables direct detection using ultraviolet absorption. The method employs polysaccharide-based chiral stationary phase and allows enantioseparation of highly stable oxazoline products in less than 6 minutes using simple binary mobile phase. As opposed to the previously used normal phase method the developed method was performed in the reversed-phase mode. Aside from the benefits of switching to less hazardous solvents with regards to the principles of Green Chemistry, this has also led to reduction of the analysis time. In comparison with known serine chromophores, the best enantioseparation of aryloxazoline rigid structure may be achieved only based on non-polar interactions with chiral stationary phase. In contrast, substitution of the chromophore moiety with hydroxyl substituent affected intra and intermolecular interactions that caused enantioseparation differences. Concurrently, we found a high chirality retention of (R)- and (S)-configuration oxazoline standards (≥ 99% e.e.) during introduction of ultraviolet label. The method is suitable for rapid injection of mixture containing the ultraviolet absorption marker without prior purification. This article is protected by copyright. All rights reserved.

Polysaccharides as separation media for the separation of proteins, peptides and stereoisomers of amino acids

Reliable separation of peptides, amino acids and proteins as accurate as possible with the maximum conformation and biological activity is crucial and essential for drug discovery. Polysaccharide, as one of the most abundant natural biopolymers with optical activity on earth, is easy to be functionalized due to lots of hydroxyl groups on glucose units. Over the last few decades, polysaccharide derivatives are gradually employed as effective separation media. The highly-ordered helical structure contributes to complex, diverse molecular recognition ability, allowing polysaccharide derivatives to selectively interact with different analytes. This article reviews the development, application and prospects of polysaccharides as separation media in the separation of proteins, peptides and amino acids in recent years. The chiral molecules mechanism, advantages, limitations, development status and challenges faced by polysaccharides as separation media in molecular recognition are summarized. Meanwhile, the direction of its continued development and future prospects are also discussed.

Negatively charged cyclodextrins: Synthesis and applications in chiral analysis-A review

The negatively charged cyclodextrins (CDs) play an important role in chiral analysis due to the additional electrostatic effect beyond the host-guest inclusion, especially in enantioanalysis of positively charged and electrically neutral analytes. This review presents recent advances in application of anionic CDs for enantioanalysis during the past five years. Firstly, the synthesis approaches of random substitution and single isomers of anionic CDs are briefly discussed. The main part focuses on the chiral analysis using anionic CDs in various analytical techniques, including capillary electrophoresis, high-performance liquid chromatography, capillary electrochromatography, counter current chromatography, nuclear magnetic resonance, etc. Particular attention is given to the capillary electrophoresis application since charged CDs could be used as a carrier of enantiomers by virtue of their self-mobility and offer an easy adjustment of the enantiomer migration order. Finally, future opportunities are also discussed in the conclusion of this review.

High-performance liquid chromatography evaluation of the enantiomeric purity of amino acids by means of automated precolumn derivatization with ortho-phthalaldehyde and chiral thiols

The use of ortho-phthalaldehyde (OPA) for the derivatization of amino acids (AA) is well known. It enables the separation of the derivatives on common reversed phase columns and improves the sensitivity with fluorescence detection. With the use of a chiral thiol an indirect enantioseparation of chiral amines and AAs is feasible. The major drawback of the OPA-derivatization is the poor stability of the products. Here, a method with an in-needle derivatization procedure is optimized to facilitate a quantitative conversion of the AA with OPA and the chiral thiols N-acetyl-L-cysteine or N-isobutyryl-L-cysteine, followed by a subsequent analysis, eluding the stability issue. Both enantiomers of a single AA were separated as OPA-derivatives with a pentafluorophenyl column and a gradient program consisting of 50 mM sodium acetate buffer pH = 5.0 and acetonitrile. Fluorescence detection is commonly used to achieve sufficient sensitivity. In this study, the enantiomeric impurity of an AA can be detected indirectly with common UV spectrophotometric detection with a limit of quantitation of 0.04%. Seventeen different L-AAs were tested and the amount of D-AA for each individual AA was calculated by means of area normalization, which ranged from not detectable up to 4.29%. The recovery of the minor enantiomer of L- and D-AA was demonstrated for three AAs at a 0.04% level and ranged between 92.3 and 113.3%, with the relative standard deviation between 1.7 and 8.2%.

Recent advances in amino acid analysis by capillary electromigration methods: June 2015-May 2017

In the tenth edition of this article focused on recent advances in amino acid analysis using capillary electrophoresis, we describe the most important research articles published on this topic during the period from June 2015 to May 2017. This article follows the format of the previous articles published in Electrophoresis. The new developments in amino acid analysis with CE mainly describe improvements in CE associated with mass spectrometry. Focusing on applications, we mostly describe clinical works, although metabolomics studies are also very important. Finally, works focusing on amino acids in food and agricultural applications are also described.

Derivatisation for separation and detection in capillary electrophoresis (2015-2017)

Derivatisation is an integrated part of many analytical workflows to enable separation and detection of the analytes. In CE, derivatisation is adapted in the four modes of pre-capillary, in-line, in-capillary, and post-capillary derivatisation. In this review, we discuss the progress in derivatisation from February 2015 to May 2017 from multiple points of view including sections about the derivatisation modes, derivatisation to improve the analyte separation and analyte detection. The advancements in derivatisation procedures, novel reagents, and applications are covered. A table summarising the 46 reviewed articles with information about analyte, sample, derivatisation route, CE method and method sensitivity is provided.