Following the first demonstrations of high-mass analysis using time-of-flight matrix-assisted laser desorption/ionization (MALDI) techniques by Hillenkamp, Tanaka and their co-workers, there have been significant efforts in a number of laboratories to adapt the new methodology to Fourier-transform mass spectrometry (FTMS). The motivation for this research is obvious. Namely, it would be desirable to couple the unparalleled high mass resolution of FTMS with the extended mass range provided by MALDI, particularly for analysis of polymers and biomolecules. Unfortunately, prior to the present work, attempts to mate FTMS and MALDI have met with limited success. The highest mass matrix-assisted laser-desorption-FTMS result previously obtained appears to be the unpublished low resolution spectrum of bovine insulin recently reported by Russell and co-workers. We, Campana and co-workers, and Hettich and Buchanan have had some success with MALDI-FTMS of biomolecules with masses lower than 3000 Da, including melittin, a variety of lower mass peptides, and oligonucleotides with masses lower than 1800 Da. Furthermore, with the single exception of Campana's report of obtaining mass resolution of 5000 for the molecular ion of melittin, such spectra have not displayed high resolution. Here, we report successful development of MALDI-FTMS, demonstrated with spectra obtained from a variety of high-mass polymer and biomolecule samples, using 355 nm radiation from an excimer-pumped dye laser for desorption/ionization and sinapinic acid as matrix. Some of these spectra are of much higher mass resolution than is possible with current time-of flight mass spectrometers.
Matrix-assisted laser desorption/ionization (MALDI)
and Fourier-transform ion cyclotron
mass spectrometry (FT-ICR-MS) are combined for the characterization of
polyoxyalkyleneamines. 1H
and 13C NMR data are used to confirm and quantify
structural assignments. Characterization of the
molecular weight distribution, chemical composition distribution, and
end group distribution of amine-terminated (co-)polymers of ethylene oxide and propylene oxide is
rather complex because the convolution
of these three entities yields an ensemble of structurally related
molecules which is hard to characterize
by conventional analytical techniques. In this study MALDI
FT-ICR-MS is used to resolve intact, Na+
cationized, oligomer ions in the mass range from m/z 500 to
3500. This revealed the presence of various
compositional distributions in the polyoxyalkyleneamines. The
individual compound masses in the
molecular weight distributions were measured with a mass accuracy of
<20 millimass units, allowing
end group and repeat unit determination with an accuracy of better than
50 millimass units. NMR is
used to measure the average end group distribution to provide insight
in conformational differences. In
this respect, FT-ICR-MS data and NMR data are complementary. The
combined results yield detailed
information about chemical composition distributions of
polyoxyalkyleneamines that hitherto it was not
possible to obtain with either technique separately.
Results from investigations of the 10.5 eV photoionization of infrared laser-desorbed, jet-entrained peptides are presented. The instrumental set-up for vacuum ultraviolet generation and the coupling to a reflectron-time-of-fight mass spectrometer is described. Single-photon ionization makes possible the investigation of molecules without any chromophoric group. Examples of the application of this ionization method to di-and tripeptides containing glycine, alanine, leucine and proline are shown. A comparison between single-and multi-photon ionization of tryptophan and tryptophan-containing peptides up to four amino acids is made and discussed in terms of soft ionization and generation of fragment ions.
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