Ionization source, nickel

Schematic of a typical ion mobility spectrometer is shown in Fig. 1. An ion mobility spectrometer consists of an ionization source, an ion mobility drift tube, a detector, and supporting electronics. The samples are usually ionized by radioactive Nickel-63, electrospray ionization source, corona discharge, or photoionization source. The ions travel through the drift tube while colliding with the medium molecules, usually air or nitrogen, at atmospheric pressure. The resulting ion velocity is proportional to the applied electric field and mobility of the ion.

Traditionally, negative mode nickel-63 is the ionization source of choice for many commercial IMS trace... 

Currently there are four commercial companies offering handheld and portable gas phase time-of-flight ion mobility spectrometers, with drift tubes shorter than 5 cm Smiths Detection, Bruker-Daltonics, GE-Interlogix, and G.A.S. Gesellschaft fiir analytische Sensorsysteme mbH. Table 1 presents their respective instruments and their major applications. These instruments generally use an applied electric field of around 250 Vcm , and they operate at either ambient or elevated temperature, and at atmospheric pressure. The samples are ionized by radioactive nickel-63 source mostly, but also by corona discharge and photo-ionization source. 

The cross-section for electron impact ionization has already been mentioned in Sect. 2.2.2.2 in connection with electron sources, and a variety of experimental and theoretical cross-sections have been shown in Fig. 2.18 for the particular case of the K-shell of nickel. The expression for the cross-section derived by Casnati et al. [2.128] gives reasonably good agreement with experiment the earlier expression of Gry-zinski [2.131] is also useful. 

Nickel electroless plating on a less noble metal is common.17 For example, the source of nickel can be nickel sulfate. The reducer can be an organic substance, such as formaldehyde. A chelating agent (tartrate or equivalent) is generally required. The nickel salt is ionized in water ... 

The electron capture detector is another type of ionization detector. Specifically, it utilizes the beta emissions of a radioactive source, often nickel-63, to cause the ionization of the carrier gas molecules, thus generating electrons that constitute an electrical current. As an electrophilic component, such as a pesticide, from the separated mixture enters this detector, the electrons from the carrier gas ionization are captured, creating an alteration in the current flow in an external circuit. This alteration is the source of the electrical signal that is amplified and sent on to the recorder. A diagram of this detector is shown in Figure 12.13. The carrier gas for this detector is either pure nitrogen or a mixture of argon and methane. 

The radioisotope cobalt-60, with a half-life of 5.27 years (1925.3 days) through beta ((3) emission, decays to form the stable element nickel-60. It is used to test welds and metal casts for flaws, to irradiate food crops to prolong freshness, as a portable source of ionizing gamma (Y) radiation, for radiation research, and for a medical source of radiation to treat cancers and other diseases. 

Thermal-ionization mass spectrometers use a hot filament to ionize the sample. The element of interest is first purified using wet chemistry and then is loaded onto a source filament, often along with another substance that makes ionization easier and a more stable function of temperature. The filament is heated and as the sample evaporates, it is ionized. Both positive and negative ions can be created by thermal ionization, depending on the electronegativity of the element to be measured. Thermal-ionization mass spectrometers are used to measure a wide variety of elements, including magnesium, calcium, titanium, iron, nickel, rubidium, strontium, neodymium, samarium, rhenium, osmium, uranium, lead, and many others. 

Electron-capture detectors show great sensitivity to halogenated compounds. In electron-capture detectors, the carrier gas is ionized by beta particles from a radioactive source (usually tritium or nickel-63), to produce a plasma of positive ions, radicals, and thermal electrons. Thermal electrons are formed as the result of the collision of high-energy electrons and the carrier gas. 

Figure 1.10 REMPI-TOF permits selective simultaneous recording of separate spectra for different cluster species or for different isotopomers. The spectra of NiC and NiSi were recorded (by resonant two-photon ionization using an ArF excimer laser to ionize) using laser ablation of a nickel target in a stream of carrier gas containing 3% CH4. No intentional source of silicon was present (but the nickel sample had been roughened using SiC sandpaper) (from Brugh and Morse, 2002, and Lindholm, et al, 2003).

Radioactive sources are favored for use in IMS analyzers because they provide stable and reliable operation, with ionization chemistry that is well suited for most current applications of IMS. Furthermore, radioactive foils do not require an external power supply and have no moving parts or maintenance requirements. At present, the most widely used and best understood of all ion sources for IMS is still the long-favored radioactive i source, which is also widely used in electron capture detectors (ECDs) for gas chromatography (GC). The preferred radioactive source is 10 mCi (3.7 10 Bq) of Ni coated as a thin layer on a metal strip, generally nickel or gold. The maximum energy of the electrons emitted from the Ni source... 

Laser-aided interfaces find applications in fundamental studies in physical chemistry (see Section 4.2.1). However, they can also be used in the monitoring of environmental matrices as well as chemical and biochemical reactions (MA)LDI-MS is the most prominent example (Section 4.2.2). Moreover, laser beams can be introduced into canonical ion sources such as ESI to enable efficient transfer of microscale aliquots of solid or liquid matrices to the ionization zone. Along these lines, Cheng et al. [143] used electrospray-assisted laser desorption/ionization (ELDI) to monitor epoxidation of chalcone in ethanol, chelation of ethylenediaminetetraacetic acid with copper and nickel ions in aqueous solution, chelation of 1,10-phenanthroline with iron(II) in methanol, and... 

Dzidic, I. Stillwell, R.N. CarroU, D.I. Homing, E.C. Comparison of Positive Ions Formed in Nickel-63 and Corona Discharge Ion Sources Using Nitrogen, Argon, Isobutane, Ammonia and Nitric Oxide as Reagents in Atmospheric Pressure Ionization Mass Spectrometry. Anal. Chem. 1976,45, 1763-1768. 

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