Ionizable species, analyzing

LIMS Laser Ionization Mass Spectroscopy Surlace, bulk U.V. laser (ns pulses) Ionized species analyzed with mass spectrometer 50-150 nm 5 (in-1 mm Elemental (micro)analysis detection limits 1-100 ppm 8... 

The instrument in my laboratory uses laser desorption ionization with a Nd YAG laser and a TOF-MS. The particles are drawn into the instrument on a continuous basis and undergo a supersonic expansion when they pass through the inlet nozzle. During the expansion, the particles pick up different speeds that are a function of their size. They then pass through two scattering lasers. The time it takes the particle to travel between the two lasers can be correlated with particle size, allowing the particle size to be determined precisely. Knowing the particle speed and position, it is possible to time its arrival at the center of the spectrometer with a Nd YAG laser pulse (266 nm). The pulse is able to desorb ionized species from the particle, which can then be analyzed by the spectrometer. 

Time of flight ion probes (TOF SIMS) have unique capabilities not found in other mass spectrometers. A pulsed ion beam, typically either cesium or gallium, ejects atoms and molecules from the sample. Ionized species are accelerated down the flight tube and the arrival time in the detector is recorded, giving the mass of the species (see discussion of time-of-flight mass analyzers above). TOF SIMS instruments used in cosmochemistry have spatial resolutions of <1 pm. They are used to determine elemental abundances in IDPs and Stardust samples. The spatial distribution of elements within a small sample can also be determined. TOF SIMS instruments can obtain good data with very little consumption of sample. 

The mass spectrometer has long been an indispensable tool in chemistry. Molecules to be analyzed, referred to as analytes, are first ionized in a vacuum. When the newly charged molecules are introduced into an electric and/or magnetic field, their paths through the field are a function of their mass-to-charge ratio, mlz. This measured property of the ionized species can be used to deduce the mass (M) of the analyte with very high precision. 

Typically, a source gas such as boron trifluoride [7637-07-2], BF3, is exposed to an ion source that causes the gas to ionize. An analyzer discriminates between all the ionic particles using a magnetic field that can select particles having the correct mass-to-charge ratio to pass through the analyzer to an acceleration tube. The ions are accelerated in the tube and collimated into a beam that is scanned over the substrate wafer. The three primary parameters of any implantation process are the type of dopant species, the accelerating energy used for implantation, and the dose of the source gas. The dose is the total number of ions that enter the wafer. Dose, ( ), can be calculated... 

Mass spectrometers are used not only to detect the masses of proteins and peptides, but also to identify the proteins, to compare patterns of proteins and peptides, and to scan tissue sections for specific masses. MS is able to do this by giving the mass-to-charge ratio of an ionized species as well as its relative abundance. For biological sample analysis, mass spectrometers are connected to an ionizing source, which is usually matrix-assisted laser desorption ionization (MALDI) [14], surface-enhanced laser desorption/ioni-zation (SELDI, a modified form of MALDI) [15], or electrospray ionization [16]. These interfaces enable the transfer of the peptides or proteins from the solid or liquid phase, respectively, to the gas (vacuum) phase inside the mass spectrometer. Both MALDI and electrospray ionization can be connected to different types of mass analyzers, such as quadrupole, quadruple-ion-traps, time of flight (TOF), or hybrid instruments such as quadrupole-TOF or Fourier transform-ion cyclotron resonance. Each of these instruments can... 

Scenario 4. Buffered eluents must be used when analyzing ionizable species, lonizable species are prone to solvation by the mobile-phase components and the solvation equilbira may lead to poor peak shapes. In Figures 8-12A and 8-12B, two acidic compounds, benzoic acid (pKa 4.2) and sorbic acid (pKa 4.8), are analyzed at pH 3.5 (a pH lower than the analyte pKa) and at pH 7.0 (a pH greater than the analyte pKa). Acceptable peak shapes are obtained at both... 

Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) is a surface analysis technique used to analyze mass and image constituents that are present on the surface of materials. The equipment (Figure 12.47) uses a pulsed primary ion beam to desorb and ionize species from the sample surface. The resulting secondary ions are accelerated into a mass spectrometer and analyzed by measuring the ToF from the sample surface to the deteetor. The location and distribution of the species on the surface can be identified and an image shown at the detector. The composition is determined from the mass spectrum. Many different primary sources can be used for ionization ... 

Fig. 6.2 Schematic of an Aerodyne aerosol mass spectrometer (AMS). Vaporized aerosol species are ionized and analyzed via mass spectrometry. This figure shows the ion attachment version of ionization methods. Other existing versions of the AMS that utilize several unique ionization methods and developments that are not shown in this schematic are discussed in the text. Extended drawing of flash vaporizer system shows that the particle beam first impacts on a vaporizer, and volatile aerosol components that vaporize are subsequently subjected to cationization. The unique feature of this detection scheme is the fact that a vaporizer is directly coupled into an ion attachment technique to enable a two-step particle vaporization and ionization process. The separation of the vaporization and ionization processes allows for quantitative detection of aerosol mass with the AMS. (Reprinted with permission from Ref [8]. 2007, John Wiley and Sons)...

---