Laser desorption mass spectra

Figure 4. Partial view of the matrix-assisted laser desorption mass spectrum of the synthetic peptide ladder from 9 to 32 residues. The formation of aspartimide (loss of water, -18u) and the piperidine adduct (+67n) are strongly observed after the synthesis of 13 residues. The weak intensity of the peak corresponding to the 14 mer is due to the low amount of 14 mer added.

Figure 1. Laser desorption mass spectrum of the glucuronic acid conjugate of 1-naphthylacetic acid ( ). The spectrum is provided by Dr. Robert Cotter.

Figure 1.14 Laser desorption mass spectrum of Compound 2, the carbon-black filled vulcanised rubber compound, obtained using the LAMMA 1000 spectrometer Reproduced with permission from Waddell and co-workers. Rubber Chemistry and...

FIGURE 6.9 Infrared laser desorption mass spectrum of the molecular-ion region of digitonin and the reference compound, phosphazine. (Reprinted with permission finom reference 9). 

FIGURE 6.15 Laser desorption mass spectrum of lysozyme using a slurry of glycerol and ultrafine metal powder as the matrix. (Reprinted with permission from reference 53). 

FIGURE 11.3 Matrix-assisted UV laser desorption mass spectrum of 40 pmol of the oligode-oxyribonucleotide TTGG (MW = 1204 Da). (Reprinted with permission from reference 5). 

This paper describes the further physical and chemical characterization of these two new forms of molecular carbon." Our results include the high-yield production (14%) of soluble material under optimized conditions, consisting of only C o and C70 in measurable quantity. These have been separated in analytical amounts by column chromatography and have been characterized in pure or mixed forms by a combination of electron impact, fast atom bombardment (FAB), and laser desorption mass spectrometry. Spectroscopic characterization is reported including the C NMR spectrum and the infrared absorption spectrum for the crude... 

Figure 1. (A) El MS spectrum of the Cjo and C70 mixture at 70 eV, with a source temperature of 340 C. Peaks markni with an X are for the ions of Csg, Cgg, C54, and C52 at m/z = 696, 672, 648, and 624, respectively. The insert shows the ion of the same sample. The ion which also appears in the spectrum is not shown. (B) FAB MS spectrum of the Cgo and C70 mixture with NOBA as the matrix. (C) Laser desorption mass spectra of pure Cgg (above) and C70 (below).

The first fullerene to be so characterized was C76-[Et91 ] The mass identification of that fraction was made by laser desorption mass spectrometry. Its NMR spectrum showed 19 lines of nearly equal intensity, implying that there were 19 distinct atomic sites, and therefore a point group... 

Figure 12.9 LDMS spectrum. Reproduced with permission from Balko, L, and J. Allison, The Direct Detection and Identification of Staining Dyes from Security Inks in the Presence of Other Colorants, on Currency and Fabrics, by Laser Desorption Mass Spectrometry, Journal of Forensic Sciences 48 (2003). Copyright 2003 ASTM International. 

Figure 8. Laser desorption of CO from a Pt(s)[7(lll) x (100)] surface following 5L exposure of CO at room temperature. In each case the mass spectrum in the region of 28p is shown.

Figure 9. Laser desorption FTMS mass spectra recorded following successive shots of the laser. In each spectrum, (a) shows the results following the first laser pulse, (b) is the second laser pulse at the same spot, (c) is after the third laser pulse, and (d) is the background spectrum (laser off).

For non-volatile sample molecules, other ionisation methods must be used, namely desorption/ionisation (DI) and nebulisation ionisation methods. In DI, the unifying aspect is the rapid addition of energy into a condensed-phase sample, with subsequent generation and release of ions into the mass analyser. In El and Cl, the processes of volatilisation and ionisation are distinct and separable in DI, they are intimately associated. In nebulisation ionisation, such as ESP or TSP, an aerosol spray is used at some stage to separate sample molecules and/or ions from the solvent liquid that carries them into the source of the mass spectrometer. Less volatile but thermally stable compounds can be thermally vaporised in the direct inlet probe (DIP) situated close to the ionising molecular beam. This DIP is standard equipment on most instruments an El spectrum results. Techniques that extend the utility of mass spectrometry to the least volatile and more labile organic molecules include FD, EHD, surface ionisation (SIMS, FAB) and matrix-assisted laser desorption (MALD) as the last... 

Meyer-Dulheuer [55] has analysed the pure additives (phenolic antioxidants, benzotriazole UV stabilisers and HALS compounds) of Table 9.8 in THF solutions by means of MALDI-ToFMS. As it turns out, polar molecules in the mass range of below 800 Da, which have a high absorption coefficient at the laser wavelength used, can often be measured without any matrix [55,56]. In this case, there is no matrix-assisted laser desorption and ionisation (MALDI) process any more. It is a simple laser desorption/ionisation (LDI) process. The advantage of this method is a matrix-free mass spectrum with the same mass resolution as in the MALDI case,... 

Microprobe laser desorption laser ionisation mass spectrometry (/xL2MS) is used to provide spatial resolution and identification of organic molecules across a meteorite sample. Tracking the chemical composition across the surface of the meteorite requires a full mass spectrum to be measured every 10 p,m across the surface. The molecules must be desorbed from the surface with minimal disruption to their chemical structure to prevent fragmentation so that the mass spectrum consists principally of parent ions. Ideally, the conventional electron bombardment ionisation technique can be replaced with an ionisation that is selective to the carbonaceous species of interest to simplify the mass spectrum. Most information will be obtained if small samples are used so that sensitivity levels should be lower than attomolar (10—18 M) fewer than 1000 molecules can be detected and above all it must be certain that the molecules came from the sample and are not introduced by the instrument itself. 

The initial observation is that PMMA is essentially completely degraded to monomer by heating to 375°C in a sealed tube while heating a mixture of red phosphorus and PMMA under identical conditions yields a solid, non-deqraded, product as well as a lower yield of monomer. One may observe, by 3C NMR spectroscopy, that the methoxy resonance is greatly decreased in intensity and methyl, methoxy phosphonium ions are observed by 31P NMR. Additional carbonyl resonances are also seen in the carbon spectrum, this correlates with a new carbonyl vibration near 1800 cm 1 in the infrared spectrum and may be assigned to the formation of anhydride. The formation of anhydride was also confirmed by assignment of mass spectra obtained by laser desorption Fourier transform mass spectroscopy, LD-FT-MS. 

We have used accurate mass measurements obtained by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOFMS) to differentiate and profile saponins from M. truncatula roots. An example is provided (Fig.3.11) showing the MALDI-TOFMS spectra of a solid-phase extract of M truncatula root tissue. In this spectrum, we can identify multiple saponins. 

Figure 15.1. MALDI spectrum of a polycarbonate sample along with peak assignment. In the inset, an expansion of the spectral region from 3.0 up to 3.7 kDa is shown. (Reproduced from Puglisi, C. et al., 1999. Analysis of Poly(bisphenol A Carbonate) by Size Exclusion Chromatography/Matrix-Assisted Laser Desorption/lonization. I. End Group and Molar Mass Determination. Rapid Communications in Mass Spectrometry, 13 2260-2267. With permission of John Wiley Sons, Inc.)...

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