Mass spectrometry analytical strategies

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. 

Budde, W.L., Analytical Mass Spectrometry Strategies for Environmental and Related Applications, American Chemical Society, Washington, D.C., 2001. 

A different strategy has been applied in our work, that emphasizes the importance of DNA stability on hole transfer within double-stranded DNA. This work is based on determination of the overall yield of oxidized nucleosides that arise from the conversion of initially generated purine and pyrimidine radical cations within DNA exposed to two-photon UVC laser pulses. On the one hand, this work benefits from the excellent current knowledge of chemical reactions involving the radical cations of DNA bases, and on the other hand, from major analytical improvements that include recent availability of the powerful technique of high performance liquid chromatography-electrospray ionization-tandem mass spectrometry (CLHP-ESI-MS/MS) [16-18]. 

In contrast to direct mass spectrometry used in the El mode, ESI often requires specific pretreatments of the samples to purify the components of interest, to increase their yield of ionisation and consequently to improve selectivity and sensitivity. It is thus not a preliminary step of analysis but a method that forms part of an analytical strategy that allows the presence of well preserved high molecular long chain compounds to be shown before their fine characterisation by ESI techniques (Regert et al., 2003a Mirabaud, 2007 Mirabaud et al., 2007). 

Figure 4.1 Analytical strategy in which direct mass spectrometry analyses using either elec tron ionisation or electrospray are used for detecting and identifying lipid substances in archaeological and museum samples...

An interesting approach is the application of multiple ion collector mass spectrometry (MC-TIMS and MC-ICP-MS) for the determination of Cd and T1 in high purity zinc metal after trace matrix separation by the certification of reference materials from the Bureau Communie de Reference (BCR).29 Accurate and precise element concentrations in high purity zinc metal have been obtained with both mass spectrometric techniques via precise isotope ratio measurements using the isotope dilution strategy the analytical data. 

The use and development of high-resolving separation techniques as well as highly accurate mass spectrometers is nowadays essential to solve the proteome complexity. Currently, more than a single electrophoretic or chromatographic step is used to separate the thousands of proteins found in a biological sample. This separation step is followed by analysis of the isolated proteins (or peptides) by mass spectrometry (MS) via the so-called soft ionization techniques, such as electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI) combined with the everyday more powerful mass spectrometers. Two fundamental analytical strategies can be employed the bottom-up and the top-down approach. 

Traditional analytical approaches such as GC-MS, HPLC fluorescence, and conventional LC-MS, are not sufficiently sensitive to quantify the low-pg/mL levels of corticosteroids in bodily fluids [4], The purpose of this work was to develop an ultrasensitive and selective approach to quantify corticosteroids present at extremely low, but biologically meaningful concentration in body fluids. A selective solid-phase extraction (SPE) and reversed-phase capillary LC coupled to tandem mass spectrometry (uLC-MS/MS) strategy was employed to achieve a high concentration sensitivity. 

These direct ion sources exist under two types liquid-phase ion sources and solid-state ion sources. In liquid-phase ion sources the analyte is in solution. This solution is introduced, by nebulization, as droplets into the source where ions are produced at atmospheric pressure and focused into the mass spectrometer through some vacuum pumping stages. Electrospray, atmospheric pressure chemical ionization and atmospheric pressure photoionization sources correspond to this type. In solid-state ion sources, the analyte is in an involatile deposit. It is obtained by various preparation methods which frequently involve the introduction of a matrix that can be either a solid or a viscous fluid. This deposit is then irradiated by energetic particles or photons that desorb ions near the surface of the deposit. These ions can be extracted by an electric field and focused towards the analyser. Matrix-assisted laser desorption, secondary ion mass spectrometry, plasma desorption and field desorption sources all use this strategy to produce ions. Fast atom bombardment uses an involatile liquid matrix. 

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