Mass spectrometry analyzers accelerator

The ToF mass analyzer is the fastest, has a broad m/z range, is one of most sensitive mass spectrometry analyzers available, and is well-suited to imaging applications. In ToF mass analysis, gas-phase ions produced by a pulsed ion source are accelerated in a high vacuum by an electric field. After being accelerated, the ions enter a field-free region between the ion source and detector at a vdocily related to their m/z ratio, with lower-m/z ions reaching the detector earlier than higher-m/z ions. 

After acceleration through an electric field, ions pass (drift) along a straight length of analyzer under vacuum and reach a detector after a time that depends on the square root of their m/z values. The mass spectrum is a record of the abundances of ions and the times (converted to m/z) they have taken to traverse the analyzer. TOP mass spectrometry is valuable for its fast response time, especially for substances of high mass that have been ionized or selected in pulses. 

Electron impact (El) ionization is one of the most classic ionization techniques used in mass spectrometry. A glowing filament produces electrons, which are then accelerated to an energy of 70 eV. The sample is vaporized into the vacuum where gas phase molecules are bombarded with electrons. One or more electrons are removed from the molecules to form odd electron ions (M+ ) or multiply charged ions. Solids, liquids and gases can be analyzed by El, if they endure vaporization without decomposition. Therefore the range of compounds which can be analyzed by El is somewhat limited to thermally stable and volatile compounds. The coupling with gas chromatography has been well established for... 

The TOF mass analyzer has a low duty cycle, and the combination with an ion accumulation device such as an ion trap is therefore very advantageous. It offers also MS capabilities with accurate mass measurement. In all acquisition modes, the ions are accelerated into the time of flight for mass analysis. Various other hybrid mass spectrometers with TOF have been described, including quadrupole ion trap [70] and linear ion trap [58]. High energy tandem mass spectrometry can be performed on TOF-TOF mass spectrometers [71, 72]. 

FIGURE 2.5. Schematic for FAB mass spectrometry. The intense activity at the surface of the sample produces neutrals, sample ions, ions from the matrix, etc. Only the ions are accelerated toward the analyzer. 

The most famous cosmogenic radionuclide is 14C (t1/2 = 5730 a), which is produced by the interaction of cosmic ray neutrons via an (n,p) reaction with nitrogen [14N(n, p)14C], whereas the radioactive decay of 14C takes place by (3 decay to form the stable 14N isotope. 14C is the most important cosmogenic radionuclide for dating (see Section 9.7.5) in archaeology and can be analyzed using isotope sensitive accelerator mass spectrometry. Extremely small isotope ratios 14C/12C = 12 in nature can be measured by means of AMS.28... 

A plasma source was coupled to a TOF-MS as early as the 1960s, when workers at Bendix [12] used such an arrangement to analyze the chemical species in a plasma jet. The instrument utilized a pulsed supersonic inlet probe similar to that found in current inductively coupled plasma mass spectrometry (ICP-MS) quadru-pole instruments and employed a TOF-MS that was oriented at a 90° angle to the input ion beam. More importantly, however, it used a pulsed extraction field to extract ions from the plasma source and accelerate them into the flight tube. It is this concept of injecting discrete ion bunches into the TOF-MS analyzer that has been almost ubiquitously employed by workers using continuous ion sources [17,18]. 

The oral aluminium bioavailability of a representative food containing food additive acidic sodium aluminium phosphate (SALP), a leavening agent in baked goods, has been studied by accelerator mass spectrometry. In the experiments, rats were fed a special diet (biscuit containing 1 % or 2% acidic SALP, synthesized to contain A1). A1, which was used as a biological tracer, can be ultrasensitively analyzed by AMS. The rats received concurrent Al infusion for comparison with oral ingestion. ... 

Very few investigations of the radiolysis of nitroalkanes have been reported, and no systematic study of their radiation chemistry has been made. Low molecular weight nitroparaffins were irradiated with y-rays from a cobalt-60 source using dose rates between 0.5 and 2.5 x 10" rad.h and the products analyzed by gas chromatography and mass spectrometry . The yield of gaseous products from irradiated nitromethane was drastically reduced if after a short irradiation, such as is obtained with a linear accelerator, the samples were immediately quenched in liquid nitrogen. Inder these conditions [Pg.668]

---