Laser desorption mass spectrometric

Wyplosz N (2003) Laser Desorption Mass Spectrometric Studies of Artists Organic Pigments. AMOLF-FOM, Amsterdam. 

First evidence for the feasibility of a cycloalkyne-to-fullerene conversion has been produced by Diederich et al. [11-13] shortly before macroscopic quantities of buckminsterfullerene Qo 1 were available [1, 14]. In Fourier-transform laser-desorption mass spectrometric (FT-LD-MS) experiments they observed that cations of cyclo-C3o 2 undergo an efficient ion-molecule coalescence to give fullerene ions such as 1+ (Scheme 1). 

Pyrolysis in the presence of tetramethylammonium hydroxide (TMAH) at a lower temperature of 300° C was studied for both PES and PSF [11]. In this study, the main component for the thermally assisted hydrolysis and methylation of PES was dimethyl derivative of bis(4-hydroxyphenyl)sulfone. This compound was formed through selective cleavages of ether linkages maintaining intact the sulfone structures. For PSF thermally assisted hydrolysis and methylation at 300° C, the main constituents were dimethyl derivative of bis(4-hydroxyphenyl)isopropylidene (bisphenol A) and also dimethyl derivative of bis(4-hydroxyphenyl)sulfone. A partial decomposition of the sulfone groups in PSF during the THM reaction also was noted. The findings also were confirmed by matrix assisted laser desorption mass spectrometric measurements. 

LD-FTMS is a valuable technique for characterisation of industrial materials. Simonsick et al. [215] analysed novel dispersants, fluorinated surfactants, and natural oils with masses in the 500-3000 Da range. Wyplosz [219] has carried out a laser desorption mass spectrometric study of artists organic pigments. The considerable potential of infrared laser desorption has yet to be fully exploited. 

Laser desorption mass spectrometric experiments revealed the presence of the TBA" " cation in the C o film after its reduction and reoxidation in 0.1 M TBAPFg solution in acetonitrile [138]. 

Fast-atom bombardment mass spectrometry (FAB-MS) has been applied to the identification of diterpenoid compounds and their oxidation products. Similarly, laser-induced desorption mass spectrometric (LDMS) techniques have been applied to the identification of natural and synthetic organic pigments in microscopic paint samples prepared as cross sections [60]. 

We have developed an analogous, but more robust system which is not necessarily constraint by the aforementioned limitations. The obvious extension has been to couple an affinity-based separation with mass spectrometry. Hutchens et al. have shown that affinity probe surfaces can be ust to capture specific protein ligands allowing detection by laser desorption mass spectrometry (. The limitations to their technique have been that the surface area for ligand capture is quite small and salt (or detergent) contaminants are still problematic. Perfusive affinity resins, on the other hand, provide a tremendous surface area for binding. The nature and composition of the solvents required for affinity chromatography, however, are not directly compatible with mass spectrometric analysis. 

Schneider, K. and Chait, B.T. (1993) Matrix-assisted laser desorption mass spectrometry of homopolymer oligodeoxynucleotides. Influence of base composition on the mass spectrometric response. Org. Mass Spectrom., 28 (11), 1353-1361. 

Carr, R.H. Jackson, A.T. Preliminary Matrix-Assisted Laser Desorption Ionization Time-of-Flight and Field Desorption Mass Spectrometric Analyses of Polymeric Methylene Diphenylene Diisocyanate, Its Amine Precursor and a Model Poly ether Prepolymer. Rapid Commun. Mass Spectrom. 1998, 12, 2047-2050. 

Berlin, K., Jain, R.K., Tetzlaff, C., Steinbeck, C. and Richeit, C., Spectrometrically monitored selection experiments Quantitative laser desorption mass spectrometry of small chemical libraries, Chem. Biol., 4 (1997) 63-77. 

Laser desorption to produce ions for mass spectrometric analysis is discussed in Chapter 2. As heating devices, lasers are convenient when much energy is needed in a very small space. A typical laser power is 10 ° W/cm. When applied to a solid, the power of a typical laser beam — a few tens of micrometers in diameter — can lead to very strong localized heating that is sufficient to vaporize the solid (ablation). Some of the factors controlling heating with lasers and laser ablation are covered in Figure 17.2. 

Laser-Induced Thermal Desorption with Fourier Transform Mass Spectrometric Detection... 

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. 

Bemdt, P., Hobohm, U., and Langen, H. (1999). Reliable automatic protein identification from matrix-assisted laser desorption/ionization mass spectrometric peptide fingerprints. Electrophoresis 20, 3521-3526. 

Krishnamurthy, T. Ross, P. L. Rapid identification of bacteria by direct matrix-assisted laser desorption/ionization mass spectrometric analysis of whole cells. Rapid Commun. Mass Spectrom. 1996,10,1992-1996. 

Holland, R. D. Rafii, F. Heinze, T. M. Sutherland, J. B. Voorhees, K. J. Lay J. O., Jr. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometric detection of bacterial biomarker proteins isolated from contaminated water, lettuce and cotton cloth. Rapid Comm. Mass Spectrom. 2000,14, 911-917. 

Lapolla A, Ragazzi E, Andretta B, et al. Multivariate analysis of matrix-assisted laser desorption/ionization mass spectrometric data related to glycoxidation products of human globins in nephropathic patients. J. Am. Soc. Mass. Spectrom. 2007 18 1018-1023. 

Figure 2.1 Mass spectrometric approach. Dl, direct inlet GC, gas chromatography HPLC, high performance liquid chromatography CZE, capillary zone electrophoresis El, electron ionization Cl, chemical ionization ESI, electrospray ionization DESI, desorption electrospray ionization APCI, atmospheric pressure chemical ionization MALDI, matrix assisted laser desorption ionization B, magnetic analyzer E, electrostatic analyzer...

Besides the well-established chromatographic/mass spectrometric or spectroscopic methods there is always a need for complementary methods for the study of organic materials from art objects. The application of laser desorption/ionisation mass spectrometry (LDI-MS) methods to such materials has been reported only sporadically [12, 45 48] however, it is apparently increasing in importance. After GALDI-MS had been applied to triterpenoid resins, as described in Section 5.2, this relatively simple method was evaluated for a wider range of binders and other organic substances used for the production or conservation of artwork. Reference substances as well as original samples from works of art were analysed. 

O.F. van den Brink, J.J. Boon, P.B. O Connor, M.C. Duursma, and R.M.A. Heeren, Matrix assisted laser desorption/ionization Fourier transform mass spectrometric analysis of oxyge nated triglycerides and phosphatidylcholines in egg tempera paint dosimeters used for environ mental monitoring of museum display conditions, J. Mass Spectrom., 36, 479 492 (2001). 

The second advantage is the possibility of performing chemical imaging analyses. Even if other techniques, such as matrix-assisted laser desorption/ionization, also allow images to be acquired, ToF-SIMS is, for now, the mass spectrometric technique with the best spatial resolution performance. 

Brancia, F.L., Oliver, S.G., and Gaskell, S.J. (2000) Improved matrix-assisted laser desorption/ionization mass spectrometric analysis of tryptic hydrolysates of proteins following guanidination of lysine-containing peptides. Rapid Comm. Mass Spectrom. 14, 2070-2073. 

By employing a laser for the photoionization (not to be confused with laser desorption/ ionization, where a laser is irradiating a surface, see Section 2.1.21) both sensitivity and selectivity are considerably enhanced. In 1970 the first mass spectrometric analysis of laser photoionized molecular species, namely H2, was performed [54]. Two years later selective two-step photoionization was used to ionize mbidium [55]. Multiphoton ionization mass spectrometry (MPI-MS) was demonstrated in the late 1970s [56—58]. The combination of tunable lasers and MS into a multidimensional analysis tool proved to be a very useful way to investigate excitation and dissociation processes, as well as to obtain mass spectrometric data [59-62]. Because of the pulsed nature of most MPI sources TOF analyzers are preferred, but in combination with continuous wave lasers quadrupole analyzers have been utilized [63]. MPI is performed on species already in the gas phase. The analyte delivery system depends on the application and can be, for example, a GC interface, thermal evaporation from a surface, secondary neutrals from a particle impact event (see Section 2.1.18), or molecular beams that are introduced through a spray interface. There is a multitude of different source geometries. 

Mass spectrometric measurements of ions desorbed/ionized from a surface by a laser beam was first performed in 1963 by Honig and Woolston [151], who utilized a pulsed mby laser with 50 p,s pulse length. Hillenkamp et al. used microscope optics to focus the laser beam diameter to 0.5 p,m [152], allowing for surface analysis with high spatial resolution. In 1978 Posthumus et al. [153] demonstrated that laser desorption /ionization (LDI, also commonly referred to as laser ionization or laser ablation) could produce spectra of nonvolatile compounds with mass > 1 kDa. For a detailed review of the early development of LDI, see Reference 154. There is no principal difference between an LDI source and a MALDI source, which is described in detail in Section 2.1.22 In LDI no particular sample preparation is required (contrary to... 

T. K. Dutta and S. Harayama. Time-of-Flight Mass Spectrometric Analysis of High-Molecular-Weight Alkanes in Crude Oil by Silver Nitrate Chemical Ionization after Laser Desorption. Anal. Chem., 73(2001) 864-869. 

T. Krishnamurthy and P. L. Ross. Rapid Identification of Bacteria by Direct Matrix-aAssisted Laser Desorption/Ionization Mass Spectrometric Analysis of Whole Cells. Rapid Commun. Mass Spectrom., 10(1996) 1992-1996. 

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