Mass electrical discharge

Thermospray interface. Provides liquid chromatographic effluent continuously through a heated capillary vaporizer tube to the mass spectrometer. Solvent molecules evaporate away from the partially vaporized liquid, and analyte ions are transmitted to the mass spectrometer s ion optics. The ionization technique must be specified, e.g., preexisting ions, salt buffer, filament, or electrical discharge. 

The most widespread modem use of mass spectrometers is to identify chemical substances. When a molecule is placed in a mass spectrometer, the electrical discharge strips away one of its electrons. This so-called parent ion has virtually the same mass as the neutral molecule. If the mass of the parent ion is measured with high enough accuracy, the data can provide the molecular formula of the substance. 

Production of ozone by irradiation or electric discharge in oxygen is readily revealed by the characteristic odor. The yield, though, is not easy to establish. In a closed system, it is very small in a flow system, it increases with the flow rate and decreases with the dose rate. These have been explained by taking the formation reaction as a three-body combination with O atom, O + 202— 03 + 02 (no chain), where the back reaction is indeed a chain process (Magee and Burton, 1951). In the mass spectrometer, 02+ is the main ion but the total yield of excited states is about the same as that of ionization (about 3.1), giving the following initial species ... 

The simplest analytical method is direct measurement of arsenic in volatile methylated arsenicals by atomic absorption [ 11 ]. A slightly more complicated system, but one that permits differentiation of the various forms of arsenic, uses reduction of the arsenic compounds to their respective arsines by treatment with sodium borohydride. The arsines are collected in a cold trap (liquid nitrogen), then vaporised separately by slow warming, and the arsenic is measured by monitoring the intensity of an arsenic spectral line, as produced by a direct current electrical discharge [1,12,13]. Essentially the same method was proposed by Talmi and Bostick [10] except that they collected the arsines in cold toluene (-5 °C), separated them on a gas chromatography column, and used a mass spectrometer as the detector. Their method had a sensitivity of 0.25 xg/l for water samples. 

Note The acronyms used here are OSPED (optical spectroscopy in a pulsed electrical discharge), FAMS (flowing afterglow mass spectrometry), SIFT (selected ion flow tube), TRAPI (time-resolved atmospheric pressure ionization mass spectrometry), PHPMS (pulsed high-pressure ionization mass spectrometry), ICRMS (ion cyclotron resonance mass spectrometry), and ADO (averaged dipole orientation collision rate theory). 

Fig. 15.15 The PTR-MS apparatus. It consists of a series of three main chambers. In the first chamber, H2O is introduced and protonated in an electrical discharge to form H3O. These ions are then driven by a small field through an orifice into the drift tube (chemical ionisation chamber). Coaxial to this orifice, neutral volatile organic compounds (VOCs) are introduced into the drift tube and collide at thermal energies with H3O. VOCs with proton affinities exceeding 166.5 kcal/mol are ionised by proton transfer from H3O and are accelerated out of the drift tube into the quadrupole mass filter and onto the detector. (Adaptedfrom [190])...

Figure 22-19 (a) Atmospheric pressure chemical ionization interface between a liquid chromatography column and a mass spectrometer. A fine aerosol Is produced by the nebulizing gas flow and the heater. The electric discharge from the corona needle creates gaseous ions from the analyte. [Adapted from E. C. Huang, T. Wachs, J. J. Conboy, and J. D. Henion, Atmospheric Pressure Ionization Mass Spectrometry," Anal. Chem. 1990,62,713A ] (b) Atmospheric pressure chemical ionization probe. [Courtesy Shimadzu Scientific Instruments, Columbia, MD.J... 

In lab-scale electrical discharge ozone generators the mass flow rate of ozone produced (m(03)) mainly depends on the gas flow rate (Qa) and the power or the voltage applied... 

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