NanoLC-EI-MS: Perspectives in Biochemical Analysis

Although LC-MS with atmospheric pressure ionization (API) sources is the primary technique used in modern bioanalytical studies, electron ionization mass spectrometry (EI-MS) can provide some substantial advantages over it. EI-MS is a matrix effect-free technique that provides reproducible and comparable mass spectra, serving as a compound fingerprint for easy identification through automated comparison with spectral libraries. Leveraging EI-MS in biochemical studies can yield critical analytical benefits for targeted and untargeted analyses. However, to fully utilize EI-MS for heavy and non-volatile molecules, a new technology that enables the coupling of liquid chromatography with EI-MS is needed. Recent advancements in nanoLC have addressed the compatibility issues between LC and EI-MS, and innovative interfacing strategies such as Direct-EI, liquid electron ionization (LEI), and Cold-EI have extended the application of EI-MS beyond the determination of volatile organic molecules. This review provides an overview of the latest developments in nanoLC-EI-MS interfacing technologies, discussing their scope and limitations. Additionally, selected examples of nanoLC-EI-MS applications in the field of biochemical analysis are presented, highlighting the potential prospects and benefits that the establishment of this technique can bring to this field.

Enantioseparation/Recognition based on nano techniques/materials

Enantiomers show different behaviors in interaction with the chiral environment. Due to their identical chemical structure and their wide application in various industries, such as agriculture, medicine, pesticide, food, and so forth, their separation is of great importance. Today, the term "nano" is frequently encountered in all fields. Technology and measuring devices are moving towards miniaturization, and the usage of nanomaterials in all sectors is expanding substantially. Given that scientists have recently attempted to apply miniaturized techniques known as nano-liquid chromatography/capillary-liquid chromatography, which were originally accomplished in 1988, as well as the widespread usage of nanomaterials for chiral resolution (back in 1989), this comprehensive study was developed. Searching the terms "nano" and "enantiomer separation" on scientific websites such as Scopus, Google Scholar, and Web of Science yields articles that either use miniaturized instruments or apply nanomaterials as chiral selectors with a variety of chemical and electrochemical detection techniques, which are discussed in this article.

Preparation of poly(N-vinylpyrrolidone-co-pentaerythritol triacrylate) monolithic column for hydrophilic interaction chromatography

A method for the preparation of poly(N-vinylpyrrolidone-co-pentaerythritol triacrylate copolymerization)-based monolithic capillary column was reported for the separation of polar small molecular weight compounds with nano-liquid chromatography in hydrophilic interaction chromatography mode. The monolithic columns were prepared by in situ copolymerization of N-vinylpyrrolidone and a cross-linker pentaerythritol triacrylate in a binary porogenic agent consisting of methanol and water. The composition of the polymerization solution was systematically optimized in terms of column permeability, theoretical plate number, asymmetric factor, and retention factor. A typical hydrophilic chromatography retention mechanism was observed with a mobile phase composed of a high content of organic solvent. The preparation method is simple and robust, the precursor N-vinylpyrrolidone is chemically stable, cheap, and easily available. The N-vinylpyrrolidone-based hydrophilic interaction chromatography stationary phase displays satisfactory separation selectivity for a range of polar test analytes, including benzoic acid derivatives, nucleosides, and phenols.

Our research cooperation with Professor Yoshio Okamoto

This article summarizes our cooperation with the research group of Prof. Yoshio Okamoto at Nagoya University during the period of time between 1992 and 2005. Although the text deals entirely with enantioseparations in high-performance liquid chromatography, capillary electrophoresis, and capillary electrochromatography, this is not a detailed review in any of these areas. The text highlights selected aspects of these techniques, which have been the subject of our joint research and in part their reflection in follow-up research by our and other research groups. Together with more systematically studied topics, aspects such as ultrafast separation of enantiomers, uncommonly high separation factor of enantiomers and other related issues are also addressed.

Nano-liquid chromatography with a new nano-structured monolithic nanocolumn for proteomics analysis

Herein, we report the preparation and application of a new nano-structured monolithic nanocolumn based on modified graphene oxide using narrow fused silica capillary column (e.g., 50 μm internal diameter). The nanocolumn was prepared by an in situ polymerization using butyl methacrylate, ethylene dimethacrylate, and methacryloyl graphene oxide nanoparticles. Dimethyl formamide and water were used as the porogenic solvent. After polymerization, the obtained nanocolumn was coated with dimethyloctadecylchlorosilane in order to enhance the hydrophobicity. Both isocratic and gradient nano-liquid chromatographic separations for small molecules (e.g., alkylbenzenes) and macromolecules (e.g., intact proteins) were performed. Theoretical plates number up to 3600 plates/m in isocratic mode for propylbenzene were achieved. It was demonstrated that the feasibility of graphene oxide modified monolithic nanocolumn for high-efficiency and high-throughput nanoscale proteomics analysis. The high resolving power of monolithic nanocolumn yielded sensitive protein separation with narrower peak width while a high-resolution analysis of peptides from trypsin-digested cytochrome C could be obtained. Graphene oxide based monolithic nanocolumns are promising and can allow to powerful tools for trace proteom sample analysis.

Recent Applications of Nano-Liquid Chromatography in Food Safety and Environmental Monitoring: A Review

In recent years, a trend toward instrument miniaturization has led to the development of new and sophisticated analytical systems, such as nano-liquid chromatography (nano-LC), which has enabled improvements of sensitivity, as well as chromatographic resolution. The growing interest in nano-LC methodology has resulted in a variety of innovative and promising applications. In this article, we review the applications of nano-LC separation methods coupled with mass spectrometry in the analysis of food and environmental samples. An assessment of sample preparation methods and analytical performance are provided, along with comparison to other, more established analytical techniques. Three main groups of compounds that are crucial for food safety assessment are considered in this review: pharmaceuticals (including antibiotics), pesticides, and mycotoxins. Recent practical applications of the nano-LC method in the determination of these compounds are discussed. Furthermore, we also focus on methods for the determination of various environmental contaminants using nano-LC methods. Future perspectives for the development of nano-LC methods are discussed.

An overview of open tubular liquid chromatography with a focus on the coupling with mass spectrometry for the analysis of small molecules

Open tubular liquid chromatography (OT-LC) can provide superior chromatographic performance and more favorable mass spectrometry (MS) detection conditions. These features could provide enhanced sensitivity when coupled with electrospray ionization sources (ESI-) and lead to unprecedented detection capabilities if interfaced with a highly structural informative electron ionization (EI) source. In the past, the exploitation of OT columns in liquid chromatography evolved slowly. However, the recent instrumental developments in capillary/nanoLC-MS created new opportunities in developing and applying OT-LC-MS. Currently, the analytical advantages of OT-LC-MS are mainly exploited in the fields of proteomics and biosciences analysis. Nevertheless, under the right conditions, OT-LC-MS can also offer superior chromatographic performance and enhanced sensitivity in analyzing small molecules. This review will provide an overview of the latest developments in OT-LC-MS, focusing on the wide variety of employed separation mechanisms, innovative stationary phases, emerging column fabrication technologies, and new OT formats. In the same way, the OT-LC's opportunities and shortcomings coupled to both ESI and EI will be discussed, highlighting the complementary character of those two ionization modes to expand the LC's detection boundaries in the performance of targeted and untargeted studies.

Stereoisomer separation of flavanones and flavanone-7-O-glycosides by means of nanoliquid chromatography employing derivatized β-cyclodextrins as mobile-phase additive

A nanoliquid chromatographic method for the stereoisomer separation of some flavanone aglycones and 7-O-glycosides has been proposed employing a C18 capillary column and a chiral mobile-phase additive such as cyclodextrin. The chiral separation of eriodictyol, naringenin, and hesperitin was obtained by addition of carboxymethyl-β-cyclodextrin to the mobile phase, whereas eriocitrin, naringin, narirutin, and hesperidin diastereoisomers were resolved by using sulfobutyl ether-β-cyclodextrin. The influence of the composition of the mobile phase, the length of the capillary column, and the flow rate on the chiral recognition were investigated. At optimum conditions, baseline separation for the selected aglycones and glycosylated forms were achieved with a mobile phase consisting of 50 mM sodium acetate buffer pH 3 and 30% methanol containing 20 mM of carboxymethyl-β-cyclodextrin and 10 mM of sulfobutyl ether-β-cyclodextrin, respectively. Precision, linearity, and sensitivity of the method were tested. Limits of detection and quantification for the studied flavanone glycosides were in the range 1.3-2.5 and 7.5-12.5 µg/mL, respectively. The method was used for the determination of the diastereomeric composition of the flavanone-7-O-glycosides in Citrus juices after solid-phase extraction procedure.