Detection MALDI

Abbreviations AOD, Acousto-optical deflection BCB, bisbenzyocyclobutadiene CCD, indirect contact conductivity detection CL, chemiluminescence ECD, electron capture detector FCS, fluorescence correlation spectroscopy FRET, fluorescence resonance energy transfer ICCD, integrated contact conductivity detection GMR, giant magnetoresistive LED-CFD, light emitting diode confocal fluorescence detector LIF, laser-induced fluorescence LOD, limit of detection MALDI, matrix-assisted laser desorption ionization PDMS, poly(dimethylsiloxane) PMMA, poly(methylmetha-crylate) SPR, surface plasmon resonance SVD, sinusoidal voltammetric detection TLS, thermal lens spectroscopy. 

External Ion Injection Similar to QIT, the analysis of volatile samples in a Penning trap is accomplished by in situ ionization with a gated electron beam. For the analysis of biomolecules, ESI and MALDI are coupled by using ion guides of the type shown in Figure 3.17. This way externally formed ions are transported into the cell for mass analysis and detection. MALDI can also be performed within the cell by aiming the laser beam at a sample target. 

The mass spectrometry (MS) of nudeic acids (NAs) has a history similar to that of proteins and other biomolecules. Although earlier work had been made possible by field desorption and fast atom bombardment (FAB) and other ionization techniques, the field did not really take off until the soft ionization techniques of electrospray ionization (ESI) [1] and MALDI [2] became available. Even with the benefits of these new ionization techniques, however, the analysis of NAs turned out to be substantially more difficult than that of proteins and, as a result, MS-based technologies are not nearly as prominent in genetics and genomics as they are in proteomics. The widespread utilization of MS for NA analysis has been further limited by the competition of powerful techniques that can rely on amplification, hybridization, and fluorescence detection. MALDI-MS has found its place in these fields only more recently, and its performance must consistently be measured against that of the competing techniques in any given analytical task. 

Yanes, O., Nazabal, A., Wenzel, R., Zenobi, R. and Aviles, F.X., Detection of noncovalent complexes in biological samples by intensity fading and high-mass detection MALDI-TOF mass spectrometry. J. Proteome Res., 5, 2711-2719 (2006). 

The structures of the macrocycles and linear polymers were analyzed by matrix-assisted laser desorption ionization with time of flight detection (MALDI-TOF) [71]. 

The chemistry of the processes occurred in the above system was studied by FTIR and matrix-assisted laser desorption ionization technique with time of flight detection (MALDI-TOF). On the basis of the results obtained, a scheme of the simultaneous and sequential reactions with formation of BP, BPT, and some intermediate and additional products, including possible substituted cyanurate, isocyanurate, and mixed triazine cycles was proposed [63]. 

Matrix-assisted laser desorption/ionization (MALDI) is widely used for the detection of organic molecules. One of the limitations of the method is a strong matrix background in low-mass (up to 500-700 Da) range. In present work an alternative approach based on the application of rough matrix-less surfaces and known as surface-assisted laser desoi ption/ionization (SALDI), has been applied. 

The unseparated digest mixture was studied directly by mass spectrometry using matrix-assisted laser desorption ionization (MALDI) and this showed six of the polypeptides detected by LC-MS and three of the expected polypeptides that had not been detected by LC-MS. In contrast, MALDI did not show three polypeptides observed by LC-MS. 

The presence of three polypeptides in Table 5.8 tliat were not predicted from the relationship between the amino acid sequence and the enzyme used for digestion is worthy of note when interpretation of data of this sort is undertaken. The MALDI data showed six further unexpected polypeptides, none of which were detected in the LC-MS data ... 

The fact that only ethylene and tetramethylethylene are evolved from exp-[8]rotane 168 and permethyl-exp-[6]rotane 173 upon thermal decomposition leads to the conclusion that the spirocyclopropane moieties in these expanded [n]rotanes fragment only externally and leave carbene moieties behind. Indeed, the MALDI-TOF mass spectra of several exp-[ ]rotanes show fragment ions with M minus 28. Thus, if this fragmentation in an exp-[n]rotane were to continue n times, a cyclic C carbon cluster would be left over. So far, however, a fragment ion with m/z = 480 corresponding to 182 has not been recorded in the mass spectrum of exp-[8]rotane 168 and it remains to be seen whether a Cgo cluster 183 will be detected in the mass spectrum of exp-[12]rotane 171 (Scheme 35). 

The extraordinary complexity of human genes and their products has encouraged the development of extremely high-resolution analytical methods.75 Capillary electrophoresis is competitive with slab gel methods, with resolution up to the order of about 1,000 base pairs for sequencing, sizing, and detection of mutation. Reversed phase HPLC is useful for restriction digest mapping and MALDI-MS up to about 1000 base pairs. 

Tables 6.27 and 6.31 show the main characteristics of ToF-MS. ToF-MS shows an optimum combination of resolution and sensitivity. ToF-MS instruments provide up to 40000 spectra s-1, a mass range exceeding 100000 (in principle unlimited), a resolution of 5000, and peak widths as short as 200 ms. This is better than quadruples and most ion traps can handle. Unlike the quadrupole-type instrument, the detector is detecting every introduced ion (high duty factor). This leads to a 20- to 100-times increase in sensitivity, compared to QMS used in scan mode. The mass range increases quadratically with the time range that is recorded. Only the ion source and detector impose the limits on the mass range. Mass accuracy in ToF-MS is sufficient to gain access to the elemental composition of a molecule. A single point is sufficient for the mass calibration of the instrument. ToF mass spectra are commonly calibrated using two known species, aluminium (27 Da) and coronene (300 Da). ToF is well established in combination with quite different ion sources like in SIMS, MALDI and ESI.

Table 9.8 shows the results of MALDI-ToFMS experiments of the selected additives in PP, HDPE, PA6 and PMMA. The observed detection limits are in the technical range of interest. Identification of the additives... 

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