Ve. Vandell et Pa. Limbach, Polyamine co-matrices for matrix-assisted laser desorption/ionization massspectrometry of oligonucleotides, RAP C MASS, 13(20), 1999, pp. 2014-2021
The analysis of oligonucleotides using matrix-assisted laser desorption/ion
ization mass spectrometry (MALDI-MS) has led to the investigation of the us
e of matrix additives (i.e., co-matrices) to help improve the poor spectral
quality commonly observed during the analysis of this class of compounds.
The use of certain matrix additives in MALDI-MS has been investigated previ
ously, and these additives have been shown to enhance the desorption/ioniza
tion efficiency of oligonucleotides during the MALDI experiment. Specifical
ly, amine bases, such as piperidine, imidazole, and triethylamine, have bee
n shown to improve mass spectral quality as assessed by improved molecular
ion resolution and increased molecular ion abundance. These improvements oc
cur due to competition between the oligonucleotide and the co-matrix for pr
otons generated during the MALDI event, Co-matrices with proton affinities
near or above the proton affinities of the nucleotide residues serve as pro
ton sinks during the desorption/ionization process, In this work, we have i
nvestigated the use of polyamines as co-matrices for MALDI mass spectrometr
ic analysis of oligonucleotides, Spermine tetrahydrochloride, spermine, spe
rmidine trihydrochloride, and spermidine were evaluated for their effective
ness at enhancing the mass spectral quality of oligonucleotides analyzed us
ing MALDI-MS, The solution-phase pK(b) values and the gas-phase proton affi
nities of these polyamines were determined, and it was found, that the poly
amines appear to be more basic than the monofunctional amines investigated
previously, The mass spectral data shows that spermidine and spermine ape e
xtremely effective co-matrices, yielding improved molecular ion resolution
and molecular ion abundances. The spermine co-matrices are more effective t
han the spermidine co-matrices, but adduction problems with the spermine co
-matrices limits their overall utility. In general, polyamine co-matrices a
re found to be more effective than monofunctional amine co-matrices at impr
oving the mass spectral data obtained during MALDI-MS of oligonucleotides,
Copyright (C) 1999 John Wiley & Sons, Ltd.