Identification of carbohydrates by matrix-free material-enhanced laser desorption/ionisation mass spectrometry

Coupling solid-phase microextraction and laser desorption ionization for rapid identification of biological material

RATIONALE

Solid phase microextraction (SPME) use small fibers directly plunged in the solution under investigation to quickly extract and quantify by different techniques the amount of selected dissolved compounds.

METHODS

Biological materials, peptides or proteins are accurately identified by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). They are difficult to extract by SPME. This work looks for a chemical to be deposited onto fibers and able to act as a good SPME extractant as well as efficient matrix for MALDI detection.

RESULTS

3-Hydroxy-2-naphthoic acid (HNA) and 2-hydroxy-1-(2-hydroxy-4-sulfo-1-naphthylazo)-3-naphthoic acid (HHSNNA) were compared to two classical matrices: α-cyano-4-hydroxycinnamic acid (CHCA) and 2,5-dihydrobenzoic acid (DHB). Bound to silica particles, DHB and HNA were found to be good MALDI matrices. Only the wide pore particles gave observable spectra. These particles were then attached in a thin layer onto wires to be used as fiber tips in SPME. Fibers loaded with peptides were introduced into the mass spectrometer to record fiber laser desorption ionization (FILDI) spectra.

CONCLUSIONS

SPME-FILDI experiments could quickly identify peptides and proteins in solutions. More work is needed to find the best matrix and the way to fix it onto the fiber.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: an update for 2007-2008

This review is the fifth update of the original review, published in 1999, on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2008. The first section of the review covers fundamental studies, fragmentation of carbohydrate ions, use of derivatives and new software developments for analysis of carbohydrate spectra. Among newer areas of method development are glycan arrays, MALDI imaging and the use of ion mobility spectrometry. The second section of the review discusses applications of MALDI MS to the analysis of different types of carbohydrate. Specific compound classes that are covered include carbohydrate polymers from plants, N- and O-linked glycans from glycoproteins, biopharmaceuticals, glycated proteins, glycolipids, glycosides and various other natural products. There is a short section on the use of MALDI mass spectrometry for the study of enzymes involved in glycan processing and a section on the use of MALDI MS to monitor products of the chemical synthesis of carbohydrates with emphasis on carbohydrate-protein complexes and glycodendrimers. Corresponding analyses by electrospray ionization now appear to outnumber those performed by MALDI and the amount of literature makes a comprehensive review on this technique impractical. However, most of the work relating to sample preparation and glycan synthesis is equally relevant to electrospray and, consequently, those proposing analyses by electrospray should also find material in this review of interest.

Determination of carbohydrates in medicinal plants--comparison between TLC, mf-MELDI-MS and GC-MS

INTRODUCTION

Quality control in the pharmaceutical and phytopharmaceutical industries requires fast and reliable methods for the analysis of raw materials and final products.

OBJECTIVE

This study evaluates different analytical approaches in order to recognise the most suitable technique for the analysis of carbohydrates in herbal drug preparations.

METHODOLOGY

The specific focus of the study is on thin-layer chromatography (TLC), gas chromatography (GC), and a newly developed mass spectrometric method, i.e. matrix free material enhanced laser desorption/ionisation time of flight mass spectrometry (mf-MELDI-MS). Samples employed in the study were standards and microwave-assisted water extracts from Quercus.

RESULTS

TLC analysis proved the presence of mono-, di- and trisaccharides within the biological sample and hinted at the existence of an unknown carbohydrate of higher oligomerisation degree. After evaluation of different derivatisation techniques, GC-MS confirmed data obtained via TLC for mono- to trisaccharides, delivering additionally quantified values under a considerable amount of time. A carbohydrate of higher oligomerisation degree could not be found. The application of mf-MELDI-MS further confirmed the presence of carbohydrates up to trisaccharides, also hinting at the presence of a form of tetrasaccharide. Besides this information, mf-MELDI-MS delivered further data about other substances present in the extract. Quantitative determination resulted in 1.750, 1.736 and 0.336 mg/mL for glucose, sucrose and raffinose respectively.

CONCLUSION

Evaluation of all three techniques employed, clearly proved the heightened performance of mf-MELDI-MS for the qualitative analysis of complex mixtures, as targets do not need modification and analysis requires only a few minutes. In addition, GC-MS is suitable for quantitative analysis.

Dihydrobenzoic acid modified nanoparticle as a MALDI-TOF MS matrix for soft ionization and structure determination of small molecules with diverse structures

Efficient structural characterization is important for quality control when developing novel materials. In this study, we demonstrated the soft ionization capability of the hybrid of immobilized silica and 2,5-dihydrobenzoic acid (DHB) on iron oxide magnetic nanoparticles in MALDI-TOF MS with a clean background. The ratio between SiO(2) and DHB was examined and was found to affect the surface immobilization of DHB on the nanoparticle, critically controlling the ionization efficiency and interference background. Compared with commercial DHB, the functionalized nanoparticle-assisted MALDI-TOF MS provided superior soft ionization with production of strong molecular ions within 5 ppm mass accuracy on a variety of new types of synthetic materials used for solar cells, light emitting devices, dendrimers, and glycolipids, including analytes with either thermally labile structures or poor protonation tendencies. In addition, the enhancements of the molecular ion signal also provided high-quality product-ion spectra allowing structural characterization and unambiguous small molecule identification. Using this technique, the structural differences among the isomers were distinguished through their characteristic fragment ions and comprehensive fragmentation patterns. With the advantages of long-term stability and simple sample preparation by deposition on a regular sample plate, the use of DHB-functionalized nanoparticles combined with high-resolution MALDI-TOF MS provides a generic platform for rapid and unambiguous structure determination of small molecules.

Online coupling of thin layer chromatography with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry: synthesis and application of a new material for the identification of carbohydrates by thin layer chromatography/matrix free material enhanced laser desorption/ionization mass spectrometry

This article describes the online hyphenation of thin layer chromatography with matrix free material enhanced laser desorption/ionization mass spectrometry (mf-MELDI-MS), the preparation of new material for MELDI and application of this newly synthesized material using TLC/MELDI-MS for the analysis of carbohydrate reference standards and plant extracts. Samples included within these analyses are standard solutions of glucose, sucrose, raffinose and a plant extract of Quercus robur, which is used for its anti-inflammatory, anti-viral and anthelminitc properties in phytomedicine. A new material for mf-MELDI-MS is prepared by immobilizing bradykinin--a peptide, on silica gel coupled to 4-(3-triethoxysilylpropylureido)azobenzene. This modification enables the absorption of laser energy sufficient for desorption and ionization of low molecular weight molecules like carbohydrates and amino acids. The newly synthesized material delivered excellent results in respect to signal-to-noise (S/N) ratio (S/N ratio: >9/1) and sensitivity (limit of detection (LOD): lower to ng/microL). Hyphenation of TLC to MELDI-MS employing the novel developed material simultaneously as chromatographic and mass spectrometric sorbent was shown for the first time for the analysis of low molecular weight molecules like mono- and oligosaccharides.

Laser desorption/ionization mass spectrometric analysis of small molecules using fullerene-derivatized silica as energy-absorbing material

In spite of the growing acceptance of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry for the analysis of a wide variety of compounds, including polymers and proteins, its use in analyzing low-molecular-weight molecules (<1000 m/z) is still limited. This is mainly due to the interference of matrix molecules in the low-mass range. Here the derivatized fullerenes covalently bound to silica particles with different pore sizes are applied as thin layer for laser desorption/ionization (LDI) mass spectrometric analysis. Thus, an interference of intrinsic matrix ions can be eliminated or minimized in comparison with the state-of-the-art weak organic acid matrices. The desorption/ionization ability of the developed fullerene-silica materials depends on the applied laser power, sample preparation and pore size of the silica particles. Thus, fullerene-silica serves as an LDI support for mass spectrometric analysis of molecules (<1500 Da). The performance of the fullerene-silica is demonstrated by the mass analysis of variety of small molecules such as carbohydrates, amino acids, peptides, phospholipids and drugs.

Identification of low molecular weight carbohydrates employing new binary mixtures for matrix-assisted laser desorption/ionisation mass spectrometry

Various energy-absorbing substances, aminopyrazine (AP), 4,4'-azodianiline (ADA), and 1-chloro-4-hydroxyisoquinoline (CHIQ), together with their binary mixtures with existing acidic MALDI matrices were subjected to matrix-assisted laser desorption/ionisation mass spectrometry (MALDI-MS) and evaluated for the analysis of low molecular weight carbohydrates. The newly introduced systems, especially AP and the combination of 2,5-dihydroxybenzoic acid and aminopyrazine (DHB-AP), have solved almost all the existing problems of the generally low sensitivity of carbohydrate analysis and of the strong background noise produced from single acidic matrices. In fact, especially at a mixing ratio of 3:1 (DHB/AP), outstanding results could be achieved, enabling the detection of analytes down to a concentration of 4 fmol/microL with mass accuracy of 37 ppm. The performance of the system was finally proven by analysing dextrins and biological samples each of which showed excellent signal intensity and signal-to-noise ratio.