Biomedical Engineering Reference
In-Depth Information
HEXAPOLE ION GUIDE
ION MOBILITY
SEPARATION
HIGH FIELD
PUSHER
T-WAVE
ION GUIDE
NON DETECTION
SYSTEM
ION
MIRROR
QUADRUPOLE
TRAP
TRANSFER
MALDI
TARGET
HELIUM CELL
AIR-COOLED TURBOMOLECULAR PUMPS
LASER
DUAL STAGE REFLECTRON
Fig. 1
The scheme of Waters MALDI SYNAPT G2 HDMS system with TOF W-mode (Reproduced
with permission from Waters Corporation)
2.4
MALDI-TOF Mass Spectrometry
A MALDI-TOF mass spectrometer is a modern TOF mass spectrometer interfaced
through a pulse laser desorption ionization technique possessing a theoretically
unlimited mass scan range, high ion-transmission efficiency, multiplex detection
capability, and simplicity in instrument design and maintenance. It can record
simultaneously all the ions produced from each single laser pulse. The basic con-
cept of TOF Mass Analyzer is that the ions are separated based on the time it takes
for the ion to drift down the flight tube to the detector with different speeds which
are inversely proportional to their mass over charge values. The lighter ions have
higher velocities than heavier ions and reach the detector first. A tandem mass spec-
trometry, such as MALDI-TOF-MS/MS, could reduce the background noise and
increase the sensitivity of the drug and its metabolites.
The MALDI-TOF has advantages on the high ion transmission, highest practical
mass range of all MS analyzers, very low detection limits. It also has some disad-
vantages, such as the fast digitizers used in TOF can have limited dynamic range,
and has limited mass measurement accuracy and limited high resolution. This was
overcome by using orthogonal acceleration technique (oa-TOF) and combining a
quadrupole mass analyzer with a TOF-MS (Q-TOF). The oa-TOF and Q-TOF sys-
tems revolutionize the application of TOF-MS system for the structural analysis
with tandem mass spectrometry. It provides high mass accuracy and resolving
power. The ion mobility separation was introduced to Q-TOF instrument that can
separate the ion with the same mass, but have different spatial shape [
72
] . Figure
1
shows an example of MALDI-TOF instrument.
