Femtosecond Laser Mass
Mass spectrometry is a highly sensitive and selective technique
suited to the analysis of organic as well as many other complex molecules.
In general, mass spectrometers operate on the principle of converting
neutral species (atoms or molecules) into gaseous ions and subsequently
separating those ions according to their mass-to-charge (m/z) ratio.
The highly selective and sensitive analytic technique of femtosecond
laser mass spectrometry (FLMS), is well suited to analytical studies
of organic molecules such as polycyclic aromatic hydrocarbons (PAHs)
and their nitro derivatives. These molecules are fused aromatic rings
and are environmental pollutants, with the highly polar nitroo-derivatives
considered to be significantly more carcinogenic.
The evolution of FLMS as an analytical
technique requires the use of methods to introduce solid-phase species
to the gas-phase for ionisation. In addition to studies of elemental
and inorganic materials, the potential of FLMS for the analysis of biomolecules
and the detection of environmentally-hazardous materials is considerable.
Recent studies have focused on coupling the TOPS femtosecond laser (800
nm, 50 fs, Intensity ~ 1015 W/cm2) with a laser
desorption source (266 nm, 16 ns) for the analysis of solid-phase labile
molecules. A technique kown as Laser Desorption/Femtosecond Laser Mass
In analytical terms, an essential feature of mass spectrometry
is the unambiguous detection of ion signals (molecular ions). In the
case of nitro-PAHs, pulses of nanosecond duration are unable to analyse
the molecules due to their rapid dissociation prior to detection. On
the other hand, pulses of femtosecond duration have been shown to ionise
virtually all classes of molecules, almost eliminating the chance of
the molecule dissociating before it is detected. In additon, at high
intensities, multiply charged atomic ions (from coulomb explosions)
and molecular are observed. Examples of the above phenomena are shown