Kai Martin

Why does matrix-assisted laser desorption/ionization time-of-flight mass spectrometry give incorrect results for broad polymer distributions?

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) is known to give reliable results for narrow molecular weight distributions, though in the case of polydisperse polymers the values obtained are not in agreement with those from conventional methods. In this paper we simulate broad polymer distributions with increasing polydispersity by mixing equimolar amounts of either poly(styrene) (PS) or poly(methylmethacrylate) (PMMA) standards in a mass range between 5000 and 100 000 Da with increasing difference in molecular weight. This allows us to investigate the problems of MALDI-TOF measurements of polydisperse polymers. We found that several reasons are responsible for the false results. High molecular weight polymers require higher laser power for the desorption/ionization process than do low molecular weight polymers. This causes smaller peak areas for the high mass component and can also be responsible for fragmentation of the low molecular weight part of a mixture, if the molecular weights of the polymers are widely distributed. The observed dependence upon laser power is different for PS and PMMA polymers and changes with the matrix used. Furthermore, doubly charged molecular peaks and molecular cluster peaks appear in the spectra and influence the experimentally measured distribution.

Poly[2]catenanes and Cyclic Oligo[2]catenanes Containing Alternating Topological and Covalent Bonds: Synthesis and Characterization

Large bifunctionalized catenate and catenand, composed of macrocycles containing 45 atoms, have been synthesized and copolymerized with a terephthalic acid derivative to afford a cyclic oligo[2]catenand and a linear poly[2]catenate. Poly[2]catenand was obtained by demetalation of poly[2]-catenate. The molecular weight distribution of these polymers, which are composed of alternating topological and covalent bonds, has been characterized by gel permeation chromatography (GPC) with universal calibration, viscometry, and MALDI-TOF mass spectrometry. We were able to synthesize a poly[2]catenate and a poly[2]catenand with a degree of polymerization (DP) equal to 8-9. In addition, an upper value of the Kuhn segment length of poly[2]catenand has been determined and is discussed in the light of its structure.

Quantitative analysis of broad molecular weight distributions obtained by matrix-assisted laser desorption ionisation-time-of-flight mass spectrometry

In order to quantify the error of matrix-assisted laser desorption ionisation (MALDI) time-of-flight (TOF) mass spectrometry in the determination of broad molecular weight distributions, different mixtures by weight of two poly(methyl methacrylate) standards were prepared. These mixtures, with well-defined bimodal molecular weight distributions were analysed by MALDI-TOF mass spectrometry using different matrices (2,4,6-trihydroxyacetophenone and 2,5-dihydroxybenzoic acid) and different cations (Li+, Na+, K+, Rb+ and Cs+) for doping the analyte. From the MALDI-TOF mass spectrometric data, the weight fractions of the two polymers of all mixtures were determined and compared to the values measured by size-exclusion chromatography. The results show that it is possible to obtain the correct Mn and Mw values with 2,5-dihydroxybenzoic acid as matrix and K+ as cationisation metal.

High-yield reactive extraction of giant fullerenes from soot

By the common Soxhlet extraction with 1,2,4-trichlorobenzene a mere 8 mass % of virgin fullerene soot can be dissolved. The extracted soot was subjected to a reactive extraction with 5-hexadecanamido-1,3-dihydro-2-benzothiophene 2,2-dioxide(4), an ortho-quinodimethane precursor. Through an irreversible Diels–Alder cycloaddition an additional 12 mass % was solubilized. Mass spectrometry, vapour pressure osmometry and elemental analysis indicate that the soluble material consists of multiple adducts of fullerenes C 60 –C 418 .

Structural analysis of phototransformed C60 by vibrational and mass spectroscopy

Abstract We report on the structural analysis of the two different phototransformed C 60 materials. The analysis was carried out by comparison of calculated Raman spectra to experimental data and by mass spectroscopy of the different species. It is demonstrated that the mass spectra of C 60 depend strongly on the desorption energy and that most of the polymeric subunits of the transformed material are destroyed upon desorption.