J. Claereboudt

Laser microprobe mass spectrometry of quaternary phosphonium salts: direct versus matrix-assisted laser desorption

The use of laser microprobe mass spectrometry (LMMS) for the structural characterization of thermolabile quaternary phosphonium salts has been evaluated. A comparison has been made between LM mass spectra obtained by direct analysis of “neat” organic salts and the corresponding “matrix-assisted” LM mass spectra. Main limitations of LMMS for the direct analysis of neat organic salts (i.e., no matrix) result from (1) formation of artifact ions that originate from thermal degradation and surface recombination reactions and (2) poor shot-to-shot reproducibility of the spectra. Dilution of the organic salts in a suitable, UV-absorbing matrix (e.g., nicotinic acid) significantly enhances the quality of the LM mass spectra. Improvements are: (1) an increase of the ion yield of preformed cations, (2) reduction or elimination of thermal decomposition and other deleterious surface reactions, and (3) a much better shot-to-shot spectral reproducibility. An interesting analytical feature is that these LM mass spectra, which contain only a few matrix peaks, can be obtained for subnanogram amounts of sample.The results also show that triphenylphosphonium salts with polycyclic aromatic substituents can be used as “molecular thermometers” to probe both the temperatures experienced by the sample molecules during the laser-induced desorption ionization process and the internal energies of the desorbed ion species. In this way, quaternary phosphonium salts can be used for evaluating whether improvements have been achieved by applying different sample treatments. Comparison of four different matrices (i.e., nicotinic acid, ammonium chloride, glycerol, and 3-nitrobenzylalcohol) indicates that the effectiveness of a matrix to reduce thermal degradation and to decrease the internal energies of the ions depends on the UV-absorption characteristics and the volatilization/sublimation temperature of the matrix material.

Fast Atom Bombardment and Tandem Mass Spectrometry for the Identification of Nucleoside Adducts with Phenyl Glycidyl Ether

Abstract The present study deals with the use of fast atom bombardment (FAB) in combination with constant neutral loss (CNL) scanning, high resolution mass spectrometry and tandem mass spectrometry (MS-MS) with collisionally activated decomposition (CAD), as complementary methods for the identification and structural analysis of phenyl glycidyl ether-nucleoside adducts. Selective detection of the parent ions of the modified nucleosides at the 1–10 ng level has been achieved by suitably designed CNL scans. The elemental composition of the adducts has been determined by accurate mass measurements. CAD-MS has been carried out on the [M + H]+ and [M - H]− ions to derive structural data on the size and nature of the base, sugar and alkyl substituent. In some cases, information on the alkylation site has been obtained, which is very useful for distinguishing isomeric adducts.

The use of laser microprobe mass spectrometry for monitoring the Wittig synthesis

Abstract Laser microprobe mass spectrometry provides a means of characterizing intermediates and reaction products of the Wittig reaction. The study of mono- and bisphosphonium halides and oligomers of xylene yields more insight in the mass spectrometric behaviour of these molecules under laser-microprobe ionization conditions.

Electron impact mass spectrometric behaviour of bis(substituted benzoato)complexes of bis(η-cyclopentadienyl)titanium(IV)

Abstract The electron impact mass spectrometric behaviour of bis(cyclopentadienyl)-bis(benzoato)titanium(IV) and related phenyl substituted complexes containing a halogen atom (Cp 2 TiL 2 , with Cp=η-C 5 H 5 ; LC 6 H 5 COO, C 6 2 H 5 COO, FC 6 H 4 COO or ClC 6 H 4 COO) is investigated with the aid of metastable ion analysis, deuterium labelling and determination of monoisotopic ion masses. Evidence is presented for the occurrence of intramolecular fluorine migrations, gas phase ion-molecule and ion-radical reactions and ortho effects.

Chromatography and Characterization of Phenylglycidyl Ether Nucleoside Adducts

Abstract The HPLC separation and structure elucidation (UV, NMR, MS) of the nucleoside adducts formed between 2′—deoxyadenosine, thymidine, 2′—deoxycytidine and 2′—deoxyguanosine with phenylglycidyl ether is described.