Matrix-assisted laser desorption mass spectrometric imaging

The second advantage is the possibility of performing chemical imaging analyses. Even if other techniques, such as matrix-assisted laser desorption/ionization, also allow images to be acquired, ToF-SIMS is, for now, the mass spectrometric technique with the best spatial resolution performance. 

Site has good software subdivision devoted to matrix-assisted laser desorption/ ionization mass spectrometric imaging (MALDI-MSI, also termed imaging MS or MS imaging). 

Hopfgartner G, Varesio E, Stoeckli M. Matrix-assisted laser desorption/ionization mass spectrometric imaging of complete rat sections using a triple quadrupole linear ion trap. Rapid Commtm Mass Spectrom 2009 23(6) 733—736. 

In Chapter 4, titled Principles of Mass Spectrometry Imaging Applicable to Thin-Layer Chromatography, the authors first introduce a budding analytical approach known as imaging mass spectrometry (IMS) strategy and then present some successful examples of its practical applications. Then, they introduce in detail three mass spectrometric techniques as those routinely used within the framework of IMS. These are secondary mass spectrometry (SIMS), matrix-assisted laser desorption/ ionization (MALDI-IMS), and desorption electrospray ionization (DESI). Finally, the authors discuss the advances and bottlenecks of these techniques when applied to TLC. 

Matrix-assisted laser desorption/ionization-tandem mass spectrometric method (MALDI-MS/MS) has proven to be a reliable tool for direct measurement of the disposition of small molecules in animal tissue sections. As example, MALDI-MS/MS imaging system was employed for visualizing the spatial distribution of astemizole and its primary metabolite in rat brain tissues. Astemizole is a second-generation antihistamine, a block peripheral HI receptor, which was introduced to provide comparable therapeutic benefit but was withdrawn in most countries due to toxicity risks. Astemizole was observed to be heterogeneously distributed to most parts of brain tissue slices including cortex, hippocampus, hypothalamic, thalamus, and ventricle regions while its major metabolite, desmethylastemizole, was only found around ventricle sites. We have shown that astemizole alone is likely to be responsible for the central nervous system (CNS) side effects when its exposures became elevated. 

Traditional mass spectrometric imaging (MSI) methods, such as matrix-assisted laser desorption ionization (MALDI) and secondary ion mass spectrometry (SIMS), have become important tools for the investigation of molecular distributions in tissues due to their high ionization efficiencies and excellent lateral and depth resolutions. Invasive sample preparation and the need for vacuum conditions, however, are incompatible with the analysis of live samples. 

The use of silver nanoparticles has also been described in matrix-assisted laser desorption/ionization (MALDI), a powerful laser-based soft ionization technique for mass spectrometric analysis and the investigation of peptides, proteins, nucleic acids, pharmaceuticals, bacterial characterization and imaging studies. Here, liquid-liquid microextraction base-modified silver nanoparticles were employed for the extraction of a hydrophobic peptide (gramicidin) from biological samples through hydrophobic interactions, prior to MALDI analysis (Figure 4.1) [41]. The application of silver nanoparticles was shown to provide an excellent sample cleanup procedure, and also assisted in the enhancement of signal of peptides and proteins. 

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