MALDI matrix properties

MALDI MATRIX PROPERTIES AND PREPARATIONS 7.2.1 Matrix Properties... 

Metabolites are small molecules that participate as substrates or products in metabolic reactions essential for the normal function of a cell. This molecular class comprises a wide range of compounds, from amino acids to lipids, organic acids, and nucleotides (11). The wide range of concentration and different chemical properties make the analysis of these compounds a challenging task. Usually, high-resolution mass spectrometers and chemical derivatization strategies are necessary to resolve isobaric interferences, increase ionization efficiency, and overcome chemical background effects from the matrix-assisted laser desorption/ionization (MALDI) matrix or the tissue matrix itself (12). 

Collectively, IM-MS clearly provides separation of lipid classes according to their charge properties, individual molecular species of a lipid class based on their molecular size (including chain length and unsaturation), and isobaric/isomeric species possessing different conformational structures [83]. This in situ drift time/collision cross section variation could be used as an additional variable to the other separation variables (e.g., intrasource separation, LC-MS elution, and optimal selection of MALDI matrix for ionization) described earlier as an aid to providing 3D analysis of complex lipid mixtures. 

Ionic liquid matrices (ILMs) introduced by Armstrong et at. were repwrted to have not only the property to make a homogeneous spot surface of analyte-matrix mixture but also the suitable properties for ionization of analytes (Anderson, J. L. et al., 2002 Armstrong, D. W. et al., 1999, 2001 Carda-Broch, S. et al., 2003). The essential point is that the ILMs consist of a conventional solid MALDI matrix, e.g., CHCA, DHB or SA and an organic base, e.g., tributylamine, pyridine or 1-methylimidazole which enables a relative state of liquidity under vacuum conditions (Tholey, A. Heinzle, E., 2006). The constituent solid matrices probably contribute to the ionization process. Several ILMs have been described and increased sensitivity analyses at the fmol or amol level have been reported for peptides and carbohydrates (Bungert, D. et al., 2004 Cramer, R. Corless, S., 2005 Crank, J. A. Armstrong, D. W., 2009 Fukuyama, Y. et al., 2008a Kaneshiro, K et al., 2011 Laremore, T. N. et al, 2006, 2007 Mank, M. et al., 2004). 

ILs can also serve as tools for the MS itself. The introduchon of the ILMs for MALDI MS has opened the way to a number of new applicahons for this method. A number of theoretical studies are necessary in order to fully understand the properties of the ILMs [36]. The basic processes of IL-MALDI are still only partially understood. Therefore, basic work remains to be done to explain theoretical aspects. The wide field of already indicated and other shll unknown applications of the ILM seems to legitimate these efforts. Up to now, no consistent relationships have been found between the composition of an ILM and its ability to serve as a good matrix—a situahon which is comparable to all other substances used as matrices. A deeper understanding of the theoretical background of the ILM is the prerequisite for a possible tailor-made creation of new matrices in the future. 

Because of expected electrical, electrochemical, optical, chemo-sensor, and other properties of the ball-type Pcs, several metallo and metal-free ball-type Pcs with different linkers have been reported. Metallo and metal free ball-type Pcs containing four calyx[4]arene units as linkers have been synthesized, Fig. 1 [37], The structures of compounds 1-3 were confirmed by UV-vis, IR, 1II-NMR, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS), and elemental analysis. Because of their unique structure and versatile complexation properties [38], calixarenes were found to be one type of interesting compounds to be incorporated into Pc. The cone conformation of the t-butylcalix[4]arene direct... 

As for ESI, the MALDI technique depends neither on the properties of the analytes nor on the absorption properties of the molecule as energy transfer proceeds via molecules of matrix. Besides, the mass or the size of the molecules does not influence the ionization and desorption process so that it can be applied to any molecule. Contrary to ESI, analyzed species are mono-charged with MALDI this simplifies the interpretation of mass spectra but this imposes working with a detector covering a wider mass (m/z) range. 

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