La spectrométrie de masse : aspect analytique

I- Regioselective anionic attachment mass spectrometry for steroid analysis

The detection and analysis of steroids is an important area of research in analytical chemistry due to both the problems of doping in sport and the impact of these compounds on health. Although mass spectrometry is a method of choice for the detection of these compounds, much progress remains to be made, particularly in terms of increasing the sensitivity of low-polarity steroids. We have recently developed a new technique consisting of regioselective anionic attachment that may allow this gain in sensitivity.

The principle of this method is simple: a small anion added to the steroid-containing solution attaches to the steroid, producing a negative ion whose signal is generally greater than that of the steroid alone. Our work has shown that the site of attachment of the anion is dependent on the nature of the anion and that regioselective anion attachment is therefore possible. We are currently developing models to better understand and predict these anion attachments. This work is carried out in partnership with the French Anti-Doping Agency (AFLD).

II- Development of new negative mode MALDI-MS arrays for use in the analysis of DNA, non-covalent complexes, and polyoxometallates

The success of the matrix-assisted desorption/ionisation (MALDI) technique often relies on sample preparation. Various fundamental studies have attempted to propose a unified model of the desorption/ionisation mechanisms. This has shown the importance of the matrix in the ablation steps and especially in the ionisation. Despite these efforts, there is a lack of priority in improving the matrices in negative mode.

This project, dedicated to the methodological development with the aim of improving the response in negative mode, is divided into several stages: the first stage will consist of the exhaustive exploration of new sample preparations, through the discovery of new matrices. In particular, this project aims to rationalise the choice of specific matrices (and/or co-matrices) for the negative ion mode according to their physicochemical properties. The second step will involve a better understanding of the mechanisms of ion formation by MALDI in the negative ion mode, by rationalising the previous developments. Some crucial experimental factors to be evaluated are: the tendency of the surface to emit electrons, then the proton affinity, and the crystalline aspect of the matrix. Finally, the third step will consist of valorising these conclusions by applying them to samples that are usually difficult to analyse, such as biomolecules (for example, DNA fragments), organometallics, nanoclusters and polyoxometallates. A thesis dedicated to this topic is starting this year.

III- Nanosystem-based mass spectrometry for ultra high mass biological agents

This project stems from our association with an ANR ASTRID bringing together LETI, the EDyP laboratory and our team. This association combines expertise in nano-systems, physics, biology and mass spectrometry instrumental development. The short-term objective of the project is to develop a NEMS mass spectrometer that will allow the analysis of macromolecular systems too large to be analysed by conventional mass spectrometry. Nano-electro-mechanical systems (NEMS) are extremely sensitive for measuring the individual inertial mass of neutral or ionised particles adsorbed on their surface. This method targets the detection of single particles, considering the problem of the capture cross-section of individual bio-nanoparticles. The long-term objective of this research is to develop a portable device with the ability to directly measure the masses of pathogens posing a bioterrorism threat. Indeed, it is of crucial importance to be able to detect and identify certain toxins quickly (Organization for the prohibition of Chemical Weapons (OPCM) Table 1).

The NEMS systems of our partner LETI are able to detect an individual neutral or weakly ionised 1 GDa particle with a resolving power of 105 to 106. With such values, NEMS-MS technology is the only technique capable of covering the needs in this [macroscopic – infinitesimal] scale segment for measuring the mass of high mass molecules of interest.

IV- Development of new high-throughput metabolomic approaches using very high resolution mass spectrometry

In order to meet large-scale health monitoring needs, it is necessary to have a methodology that can highlight the actual exposure status of the population to chemical risk, in particular the combined long-term and low-dose exposure of several xenobiotics. It is interesting in this perspective to use metabolomic approaches, which consist in highlighting disturbances of the general metabolism thanks to the modifications observed in the analytical fingerprints. However, a metabolomic study involves the spectral analysis of a large number of samples, leading to generally long analysis times.
We are seeking to develop expertise in metabolomics (the study of low molecular weight biomarkers). This research work has been carried out for several years in collaboration with INRA (Estelle Paris, Alain Paris) and the CEA (Christophe Junot). We are therefore continuing our association with this project, which aims to develop and validate new methodologies using very high resolution mass spectrometry to carry out high-throughput metabolomic approaches on different biological matrices. This work will be carried out on our very high resolution mass spectrometry instruments such as the FT-ICR-MS and the LTQ-Orbitrap. Very high resolution mass spectrometry is a very promising tool for the direct analysis of metabolites present in a mixture in a complex matrix without the need for chromatographic separation, especially in high-throughput metabolomics studies, as well as in the characterisation of the xenometabolome and the food metabolome. The method will be developed using biological samples from cohorts available at INRA or CEA, for which LC/MS or UPLC/MS analyses that have already been performed will serve as a reference. The project also aims to create a very high-resolution reference metabolomics database and MS/MS experiments to enable the high-throughput characterisation of potential biomarkers (two theses in progress, one of which will be started in 2011). Translated with (free version)

Figure 4 : Stratégie appliquée pour la métabolomique.