Time-of-flight secondary ion mass spectrometry of matrix-diluted oligo- and polypeptides bombarded with slow and fast projectiles: Positive and negative matrix and analyte ion yields, background signals, and sample aging
K. Wittmaack et al., Time-of-flight secondary ion mass spectrometry of matrix-diluted oligo- and polypeptides bombarded with slow and fast projectiles: Positive and negative matrix and analyte ion yields, background signals, and sample aging, J AM SOC M, 11(6), 2000, pp. 553-563
Citations number
39
Categorie Soggetti
Spectroscopy /Instrumentation/Analytical Sciences
Journal title
JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY
Human angiotensin II, chain B of bovine insulin, and porcine insulin were d
etermined by time-of-flight secondary ion mass spectrometry under impact of
similar to 25 keV Xe+ and SF5+ ion beams and similar to 100 MeV Cf-252 fis
sion fragments. Matrix-embedded samples, dissolved in a large surplus of al
pha-cyano-4-hydroxycinnamic acid, were prepared by nebulizer spray depositi
on, neat samples by the droplet technique. It is shown that the status of t
he sample can be assessed by evaluating the matrix-specific features of the
mass spectra. The beneficial effect of matrix isolation was small for angi
otensin but large for the insulin samples, which did not show parent peaks
from neat material. Negative ion yields under SF5+ impact were up to a fact
or of 50 higher than with Xe+. For positive secondary ions, the enhancement
was much smaller. The mass spectra produced by slow ion beams or fast fiss
ion fragments were qualitatively similar. Quantitative differences include
the following: with fast projectiles the yields were about 10-30 times high
er than with slow ions, but similar for negative ion emission under SF5+ bo
mbardment; the analyte-to-matrix yield ratios were higher with slow ions an
d up to 250 times higher than the molar analyte concentration; for analyte
ions the peak-to-background ratios were higher using slow projectiles; the
fraction of carbon-rich collisionally formed molecular ions was much higher
with fast projectiles. Sample aging in vacuum for up to five weeks strongl
y reduced the yield of protonated analyte molecules ejected by slow ion imp
act, but not of deprotonated species. Hence protonation seems to correlate
with sample "wetness" or the presence of volatile proton-donating additives
. (J Am Soc Mass Spectrom 2000, 11, 553-563) (C) 2000 American Society for
Mass Spectrometry.