Dissociation of positively charged aliphatic epoxides. II. [C5H10O]+˙ epoxides and α,β unsaturated ethers

The unimolecular dissociations of C₅ epoxides ions mono- or disubstituted at C₁ give exclusive loss of CH₃ and exclusive formation of methoxy vinyl carbenium ion, both in the source and in the 2nd field-free region. In the case of the 1,2-disubstituted ion in the 2nd field-free region the loss of ethene is the only pathway, while a competition occurs for the trisubstituted ion leading to [C₃H₆O]⁺˙ and [C₄H₇O]⁺˙ ions, the structure of which are demonstrated. The first step of the different mechanisms is the cleavage of the heterocyclic C? C bond.     

Rearrangements 1,3 en Serie Heterocyclique. VI—Fragmentation,en Spectrometrie de Masse,des Aryl-2 Alkyl-4 Oxadiazol-1,3,4 Ones-5 et des Aryl-2 Alcoxy-5 Oxadiazoles-1,3,4

The mass spectra of 2-aryl-4-alkyl-1,3,4-oxadiazole-5-ones and their 2-aryl-5-alkoxy 1,3,4-oxadiazole isomers have been studied. Unimolecular electron impact-induced isomerization does not seem to occur during the fragmentation of these compounds. For each type of heterocycle, the hydrogen transfers, during the cleavage of the alkyl chain, are mainly caused by the nitrogen in position 4.     

Detection of 28 neurotransmitters and related compounds in biological fluids by liquid chromatography/tandem mass spectrometry

This work presents two liquid chromatography/tandem mass spectrometry (LC/MS/MS) acquisition modes: multiple reaction monitoring (MRM) and neutral loss scan (NL), for the analysis of 28 compounds in a mixture. This mixture includes 21 compounds related to the metabolism of three amino acids: tyrosine, tryptophan and glutamic acid, two pterins and five deuterated compounds used as internal standards. The identification of compounds is achieved using the retention times (RT) and the characteristic fragmentations of ionized compounds. The acquisition modes used for the detection of characteristic ions turned out to be complementary: the identification of expected compounds only is feasible by MRM while expected and unexpected compounds are detected by NL. In the first part of this work, the fragmentations characterizing each molecule of interest are described. These fragmentations are used in the second part for the detection by MRM and NL of selected compounds in mixture with and without biological fluids. Any preliminary extraction precedes the analysis of compounds in biological fluids.