Laser desorption/ionization mass spectrometry LDI-MS

Figure 4.2 Demonstration of analytical lateral resolution. Scanning laser desorption/ ionization-mass spectrometry (LDI-MS) of the edge between a red and a green felt tip pen coating. Red channel m/z= 122u, anaiyiK...

Direct Laser Desorption/Ionization Mass Spectrometry (LDI-MS) An alternative technique used to eliminate matrix and cationization salt effects is LDI. 

Experimental design of time-resolved mass spectrometry (TRMS) systems can greatly affect temporal resolution in the analysis of dynamic samples (see also Section 4.2). The two popular MS approaches - laser desorption/ionization (LDI)-MS and electrospray ionization (ESI)-MS - are suitable for studies of enzymatic reactions [8]. 

Figure 3.11 summarizes such key experimental points. As a first point, we have to choose the appropriate ionization method for the detection of small metabolites, we have alternative choices other than MALDI, such as secondary ion mass spectrometry (SIMS) [15], nanostructure-initiator mass spectrometry (NIMS) [20,21], desorption/ionization on silicon (DIOS) [22], nanoparticle-assisted laser desorptiopn/ ionization (nano-PALDI) [23], and even laser desorption/ionization (LDI) [24,25]. We consider that MALDI is stiU the most versatile method, particularly due to the soft ionization capability of intact analyte. However, other methods each have unique advantages for example, SIMS and nano-PALDI have achieved higher spatial resolution than conventional MALDI-IMS, and above aU, these mentioned alternative methods are all matrix-free methods, and thus can exclude the interruption of the matrix cluster ion. Next, if MALDI is chosen, experimenters should choose a suitable matrix compound, solvent composition, and further matrix application method for their target analyte. All these factors are critical to obtain sufficient sensitivity because they affect efficiency of analyte extraction, condition of cocrystallization, and, above all, analyte-ionization efficiency. In addition, based on the charge state of the analyte molecule, suitable MS polarity (i.e., positive/ negative ion detection mode) should be used in MS measurement. Below, we shall describe the key experimental points for MALDI-IMS applications of representative metabolites. 

All films were free from cracks and defects and thick enough for laser desorption ionization-Fourier transform ion cyclotron resonance-mass spectrometry (LDI-FTICR-MS) spectra to be rid of the silicon signal (Si-H at mass-to-charge ratio [m/z] = 28). 

In 1993, Hutchens and co-workers described surface-enhanced laser desorption/ionization (SELDI) technique, an affinity technology, which has progressed over the last decade to become a powerful analytical, an on-plate approach (Hutchens and Yip 1993). SELDI is a distinctive form of laser desorption/ionization (LDI) mass spectrometry in which the EDI probe plays an active role in the homogenization, preconcentration, amplification, purification, extraction, enrichment digestion, derivatization, synthesis, separation, and detection with complementary techniques, prior to the desorption and ionization of the analytes by MALDI (Merchant and Weinberger 2000). The principle of this approach is very simple. Biomolecules are captured by adsorption, partition, electrostatic interaction, or affinity chromatography on a solid-phase protein chip surface. Although SELDI provides a unique sample preparation platform, it is similar to MALDI-MS in that a laser... 

IMS experiments may be performed using one of several MS ionization techniques secondary ion mass spectrometry (SIMS), laser desorption/ionization (LDI), desorption electrospray ionization (DESI), and matrix-assisted laser desorption/ionization (MALDI) (2). In general, these techniques offer complementary capabilities (3). SIMS imaging is favored for higher spatial resolution imaging over a low mass range (<1,000 Da), MALDI IMS covers a much wider mass range (up to and over 100,000 Da) but at somewhat lower spatial resolution, and DESI uses ambient pressure for analysis of small molecules but at lower spatial resolution. 

A few MS techniques have been available for the analysis of intractable polymers for a number of years. The most significant of these are laser desorption/ionization (LDI) (45) and secondary ion mass spectrometry (46). The major drawback with these techniques is the low production of intact molecular ions for the oligomers, especially with increasing molar mass. Another approach has been to use chemical modifications in order to make the polymer soluble in a particular solvent so that MS analysis can be conducted. However, these modifications are both time consuming and alter the original molecular structure of the polymer of interest. 

Acevedo, S., Cordero, J.M., Carrier, H., Bouyssuere, B., Lobinski, R. 2009. Trapping of paraffin and other compounds by asphaltenes detected by laser desorption ionization-time of flight mass spectrometry (LDI-TOF MS) Role of A1 and A2 asphaltene fractions in this trapping. Energy Fuels 23 842-848. 

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