Low-molecular-weight model study of peroxide cross-linking of ethylene-propylene (-diene) rubber using gas chromatography and mass spectrometry I. Combination reactions of alkanes.

The combination reaction of linear and branched alkanes, initiated by dicumylperoxide, has been studied as a model for the combination cross-linking reaction of peroxide-cured terpolymerised ethylene, propylene and diene monomer. Both gas chromatography-mass spectrometry (GC-MS) and comprehensive two-dimensional GC-MS (GCxGC-MS) analyses have been employed to analyse the isomeric reaction products. The identification of these products based on their MS fragmentation patterns is quite complex, due to the high tendency of random rearrangements. Careful elucidation of the high-mass ions at optimised ionisation energy (55eV) has resulted in proposed structures for the different isomeric reaction products. The structure assignment by MS is in agreement with the GCxGC elution pattern and with the result of a theoretical model to predict the boiling points and, thus, the GC retention times. In addition, a model that provided a direct correlation between chemical structure and retention times was developed and this was found to provide a useful fit. Quantification of the identified reaction products by GC separation and flame ionization detection allows classification according to the hydrogen abstraction sites for the alkanes by dicumylperoxide. The selectivity for hydrogen abstraction generally follows the expected order, but a higher reactivity was observed for the methylene group next to a primary methyl group, while a reduced reactivity of the methylene group next to ethyl and to methyl groups was observed. The used approach proved to be a very powerful tool to enhance our understanding of the mechanism of peroxide cross-linking of (branched) alkanes.

['Proteomics': the mapping of all human proteins]. / 'Proteomics': het in kaart brengen van alle humane eiwitten.

The genomes of many organisms, including humans, are now largely known. In the wake of this there is a need to identify and measure all proteins that are encoded by the genome (proteomics). This need leads to turbulent developments in the area of analytical techniques, such as two-dimensional electrophoresis, mass spectrometry, and protein chips. The rapidity of advancements justifies the expectation that in the next 5-10 years it will indeed become possible to determine the proteome of an organism or its components such as plasma, serum, or tissues. In combination with information on initiation and progress of disease, proteomics will contribute to improving health and to better primary and secondary prevention.