Resonant desorption

Fig. 3. Yield of resonant desorption of CH3F molecules from NaCl surfaces versus laser fluence. NaCl temperature 77 K. Basic pressure 1.6 X lO" mbar (5c).

Spectrometric Analysis. Remarkable developments ia mass spectrometry (ms) and nuclear magnetic resonance methods (nmr), eg, secondary ion mass spectrometry (sims), plasma desorption (pd), thermospray (tsp), two or three dimensional nmr, high resolution nmr of soHds, give useful stmcture analysis information (131). Because nmr analysis of or N-labeled amino acids enables determiaation of amino acids without isolation from organic samples, and without destroyiag the sample, amino acid metaboHsm can be dynamically analy2ed (132). Proteia metaboHsm and biosynthesis of many important metaboUtes have been studied by this method. Preparative methods for labeled compounds have been reviewed (133). 

Tandem mass spectrometry (MS/MS) is a method for obtaining sequence and structural information by measurement of the mass-to-charge ratios of ionized molecules before and after dissociation reactions within a mass spectrometer which consists essentially of two mass spectrometers in tandem. In the first step, precursor ions are selected for further fragmentation by energy impact and interaction with a collision gas. The generated product ions can be analyzed by a second scan step. MS/MS measurements of peptides can be performed using electrospray or matrix-assisted laser desorption/ionization in combination with triple quadruple, ion trap, quadrupole-TOF (time-of-flight), TOF-TOF or ion cyclotron resonance MS. Tandem... 

To check the identity and purity of the products obtained in the above reactions it is not sufficient to analyze for the sulfur content since a mixture may incidentally have the same S content. Either X-ray diffraction on single crystals or Raman spectra of powder-like or crystalline samples will help to identify the anion(s) present in the product. However, the most convincing information comes from laser desorption Fourier transform ion cyclotron resonance (FTICR) mass spectra in the negative ion mode (LD mass spectra). It has been demonstrated that pure samples of K2S3 and K2S5 show peaks originating from S radical anions which are of the same size as the dianions in the particular sample no fragment ions of this type were observed [28]. 

Bob Ardrey obtained a first degree in Chemistry from the University of Surrey where he went on to obtain his doctorate stndying the chemistry of trans-2,3-dichloro-l,4-dioxan and the stereochemistry of its reaction prodncts using primarily mass spectrometry and nnclear magnetic resonance spectroscopy. He then carried ont post-doctoral research at King s College, London, into the development of emitters for field-desorption mass spectrometry. 

We have also carried out preliminary experiments in which we have detected the laser desorption of ethylene, cyanogen, methanol, and benzene from the Pt(s)[7(111) x (100)] surface. These spectra are shown in Figure 9. In the experiments involving ethylene, cyanogen, and methanol only neutral species are desorbed. In the case of benzene we observe the molecular parent ion in the absence of the electron beam. We believe that this is due to resonance multiphoton ionization of the benzene by the laser after desorption (resonance multiphoton ionization of benzene is very efficient with 249 nm radiation). These spectra are in marked contrast to the results of SIMS experiments which produce a wide variety of complex metal-adsorbate cluster ions. In the case of ethylene, our experiments were performed at 140 K, and under these conditions ethylene is known to be a molecular x-bonded species on the surface. In SIMS under these conditions the predominant species is CH (15)t but in the laser desorption FTMS experiments neutral ethylene is the principal species detected at low laser power. 

Field desorption mass spectrometry [1606], C nuclear magnetic resonance, and fourier-transform infrared spectroscopy [1337] have been used to characterize oil field chemicals, among them, scale inhibitors. Ion... 

Alternative approaches consist in heat extraction by means of thermal analysis, thermal volatilisation and (laser) desorption techniques, or pyrolysis. In most cases mass spectrometric detection modes are used. Early MS work has focused on thermal desorption of the additives from the bulk polymer, followed by electron impact ionisation (El) [98,100], Cl [100,107] and field ionisation (FI) [100]. These methods are limited in that the polymer additives must be both stable and volatile at the higher temperatures, which is not always the case since many additives are thermally labile. More recently, soft ionisation methods have been applied to the analysis of additives from bulk polymeric material. These ionisation methods include FAB [100] and LD [97,108], which may provide qualitative information with minimal sample pretreatment. A comparison with FAB [97] has shown that LD Fourier transform ion cyclotron resonance (LD-FTTCR) is superior for polymer additive identification by giving less molecular ion fragmentation. While PyGC-MS is a much-used tool for the analysis of rubber compounds (both for the characterisation of the polymer and additives), as shown in Section 2.2, its usefulness for the in situ in-polymer additive analysis is equally acknowledged. 

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. 

Shumaker Parry, J. S. Campbell, C. T., Quantitative methods for spatially resolved adsorption/desorption measurements in real time by surface plasmon resonance microscopy, Anal. Chem. 2004, 76, 907 917... 

DGE a AC AMS APCI API AP-MALDI APPI ASAP BIRD c CAD CE CF CF-FAB Cl CID cw CZE Da DAPCI DART DC DE DESI DIOS DTIMS EC ECD El ELDI EM ESI ETD eV f FAB FAIMS FD FI FT FTICR two-dimensional gel electrophoresis atto, 10 18 alternating current accelerator mass spectrometry atmospheric pressure chemical ionization atmospheric pressure ionization atmospheric pressure matrix-assisted laser desorption/ionization atmospheric pressure photoionization atmospheric-pressure solids analysis probe blackbody infrared radiative dissociation centi, 10-2 collision-activated dissociation capillary electrophoresis continuous flow continuous flow fast atom bombardment chemical ionization collision-induced dissociation continuous wave capillary zone electrophoresis dalton desorption atmospheric pressure chemical ionization direct analysis in real time direct current delayed extraction desorption electrospray ionization desorption/ionization on silicon drift tube ion mobility spectrometry electrochromatography electron capture dissociation electron ionization electrospray-assisted laser desorption/ionization electron multiplier electrospray ionization electron transfer dissociation electron volt femto, 1CT15 fast atom bombardment field asymmetric waveform ion mobility spectrometry field desorption field ionization Fourier transform Fourier transform ion cyclotron resonance... 

J. S. Sampson, A. M. Hawkridge, and D. C. Muddiman. Generation and Detection of Multiply-Charged Peptides and Proteins by Matrix-Assisted Laser Desorption Electrospray Ionization (MALDESI) Fourier Transform Ion Cyclotron Resonance Mass Spectrometry. J. Am. Soc. Mass Spectrom., 17(2006) 1712-1716. 

Electron spin resonance (esr), 22 132 for lignin characterization, 15 10 Electron-stimulated desorption-ion angular distribution (ESDIAD), 24 74 Electron transfer (ET), 9 376-381, 388 mechanisms of, 13 444 rate constant for, 13 447 Electron-transfer dynamics, in... 

Laser desorption (LD) Fourier transform ion cyclotron resonance MS (FTICR-MS) in the positive mode was applied for the analysis of... 

For the characterisation of the biodegradation intermediates of C12-LAS, metabolised in pure culture by an a-proteobacterium, Cook and co-workers [23] used matrix-assisted laser desorption/ionisation (MALDI)-time of flight (TOF)-MS as a complementary tool to HPLC with diode array detection and 1H-nuclear magnetic resonance. The dominating signal in the spectrum at m/z 271 and 293 were assigned to the ions [M - H] and [M - 2H + Na]- of C6-SPC. Of minor intensity were the ions with m/z 285 and 299, interpreted to be the deprotonated molecular ions of C7- and C8-SPC, respectively. 

Octadecyl sulfate sodium salt (Ci8H37-0-S03 Na+) was examined by laser desorption (LD) Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) in the negative mode resulting in [M - H] ions. Little fragmentation was observed under these conditions [28]. 

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