3‐Hydroxypicolinic Acid as an Effective Matrix for Sophorolipid Structural Elucidation Using Matrix‐Assisted Laser Desorption Ionization Time‐of‐Flight Mass Spectrometry

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2019-2020

This review is the tenth update of the original article published in 1999 on the application of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2020. Also included are papers that describe methods appropriate to analysis by MALDI, such as sample preparation techniques, even though the ionization method is not MALDI. The review is basically divided into three sections: (1) general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation, quantification and the use of arrays. (2) Applications to various structural types such as oligo- and polysaccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals, and (3) other areas such as medicine, industrial processes and glycan synthesis where MALDI is extensively used. Much of the material relating to applications is presented in tabular form. The reported work shows increasing use of incorporation of new techniques such as ion mobility and the enormous impact that MALDI imaging is having. MALDI, although invented nearly 40 years ago is still an ideal technique for carbohydrate analysis and advancements in the technique and range of applications show little sign of diminishing.

Composite PVK/SLGO As Matrix for MALDI-TOF MS Detection of Small Molecules in Dual-Ion Mode

Currently, most matrices developed for matrix-assisted laser desorption/ionization mass spectrometry (MALDI-TOF MS) for small-molecule detection are only suitable for the positive or negative ion mode and not the dual-ion mode, except for carbon-based nanomaterials. The lone-pair electrons on the N atom in poly n-vinylcarbazole (PVK) can serve as a Lewis base with strong electron-donation effects, which is favorable for negative ion mode detection. The surface of single-layer graphene oxide (SLGO) contains many oxygen atoms in carboxyl and hydroxyl groups that act as Lewis acids and thereby provides favorable protonation sites for positive ion mode detection. In this study, composite PVK/SLGO was prepared by combining the advantages of amorphous PVK and SLGO. PVK/SLGO was tested as a novel matrix for positive- and negative-ion-mode MALDI-TOF MS for the analysis of amino acids, nucleic acid bases, environmental endocrine disruptors, antibiotics, and various small molecules. PVK/SLGO was compared with PVK, SLGO, and commercially available matrices of 9-aminoacridine (9-AA) and α-cyano-4-hydroxycinnamic acid (CHCA). The PVK/SLGO matrix was demonstrated to be suitable for the positive and negative ion modes, exhibiting high signal intensity and detection sensitivity without background interference. The limits of detection of the aforementioned molecules ranged from 0.1 to 0.0001 and 0.01 to 0.0001 mg/mL in the positive and negative ion modes, respectively. The quantitative determination of enrofloxacin in milk was realized using an internal standard method with a linear range of 0.0001-0.1 mg/mL (R ² = 0.9991). Furthermore, the PVK/SLGO matrix exhibited high salt tolerance (up to 1000 mmol/L) and stability over 28 consecutive days. Studies regarding its ionization mechanism revealed that the good performance originates from the combined materials acting synergistically. This study provides a foundation for developing bimodal composite matrices and further expands the scope of PVK/SLGO applications.

Mass spectrometry-based lipid analysis and imaging

Mass spectrometry imaging (MSI) is a powerful tool for in situ mapping of analytes across a sample. With growing interest in lipid biochemistry, the ability to perform such mapping without antibodies has opened many opportunities for MSI and lipid analysis. Herein, we discuss the basics of MSI with particular emphasis on MALDI mass spectrometry and lipid analysis. A discussion of critical advancements as well as protocol details are provided to the reader. In addition, strategies for improving the detection of lipids, as well as applications in biomedical research, are presented.