Analytical Techniques Overview
In Time of Flight Laser Ionization Mass Spectrometry a focussed laser beam ablates neutral particles from the sample surface that are indiscriminately ionized by a second powerful laser source using the process of nonresonant multiphoton ionization (NRMPI). Surface analysis of inorganic species with high elemental and surface sensitivity.
TOF-Secondary Ion Mass Spectrometry generally operates in a static SIMS mode whereby the top monolayers of the sample surface are analyzed. A pulsed ion beam is used and secondary ions emitted from compounds and molecules are mass analyzed and imaged.
In Vacuum Ultra Violet TOF-LIMS a laser beam desorbs unfragmented molecules, which are ionized by VUV (Vacuum Ultraviolet) radiation with minimal fragmentation. These are mass analyzed in a time-of-flight mass spectrometer.
When the surface of a sample is excited with X-rays, high-resolution energy analysis of photoelectrons emitted from atoms near the surface can be used to characterize a variety of inorganic and organic materials. Chemical bonding information may be determined from the chemical shift of atomic transitions. X-ray Photoelectron Spectroscopy is also known as ESCA.
SEM, EPMA & AIA
In Scanning Electron Microscopy, Electron Probe Microanalysis and AIA a finely focused electron beam is rastered over the sample’s surface from which an image is formed from the particles produced (e.g. secondary/backscattered electron and photon emission). Combined with energy dispersive X-ray (EDX) spectroscopy elemental quantification is possible. Wavelength dispersive X-ray (WDX) spectroscopy offers improved sensitivity.
While other techniques focus on analyzing individual mineral particles, Automated Image Analysis (AIA) analyzes backscattered electron or EDX compositional dot maps from SEM for mineral abundances.
In micro-Particle Induced X-ray Emission spectroscopy a high energy proton beam is focused on a mineral particle to generate characteristic X-rays for elemental detection. Simultaneous multielemental detection and mapping of trace elements with superior sensitivity.
Secondary Ion Mass Spectrometry, operated in a dynamic mode, an energetic primary ion beam is used to sputter atoms from the sample surface. Secondary ions emitted are mass analyzed using a double focusing electrostatic magnetic sector instrument. Very high sensitivity and quantitative analysis are key features. Depth profiling and imaging capabilities.
In TOF-Resonant Ionization Mass Spectrometry after a laser ablation, only one specific atomic species is resonantly (i.e. selectively) excited and ionized by a second tunable laser source. For ultimate elemental sensitivity and quantitative analysis.