Matrix Assisted Laser Desorption
Ionisation-Time of Flight Mass Spectrometer (MALDI-TOF)
Bruker OmniFlex. This instrument is primarily used for peptide mass fingerprinting and, after appropriate training, is user operated.
In addition to peptides,
this instrument may also be used to analyse oligonucleotides,
and other compounds of biological origin as well as synthetic
polymers. The amount of sample needed is very low (pmoles
and less). The sample is typically co-crystallised with
a matrix (often a small aromatic acid eg α-cyano-4-hydroxycinnamic
acid for peptides) onto a stainless steel target or onto
an Anchor Chip which has a hydrophobic surface designed
to concentrate the sample into a small area. The dried sample
is then illuminated with a pulse of laser light. The laser
energy is absorbed by the matrix and transferred to the
analyte which is then desorbed from the target into the
gas phase and ionised. Singly charged ions are usually produced.
The MS analyser in this instrument is a time of flight analyser
(Tof) fitted with a reflectron to enhance mass resolution.
The analyser can be operated in the linear mode (high mass,
low resolution) up to a molecular weight of m/z 300,000
(in rare cases) or in reflectron mode (lower mass, higher
resolution) up to a molecular weight of 10,000.
While
MALDI is reputed to be relatively insensitive to contaminants
(e.g. buffers, detergents, and salts), it must be said that
the cleaner the sampler, the better the sensitivity and
the better the coverage of analytes because ionisation suppression
is reduced. Some structural information (e.g. amino
acid sequence of peptides) can be obtained by post-source
decay (PSD).
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