Ion source electron impact

To identify the isomeric form of the product of the collisionally stabilized analog of reaction 44 experimentally, Scott et al.92 studied reactions of C3H30+ (C2Hj/CO) produced in that reaction and compared it with that produced directly from propynal in an electron impact ion source or by proton transfer from HCO+ to propynal in the flow tube (these latter two production methods yielded ions with... 

Meier, K. Seibl, J. Measurement of Ion Residence Times in a Commercial Electron Impact Ion Source. Int. J. Mass Spectrom. Ion Phys. 1974,14, 99-106. 

Brunnee, C. A Combined Field Ionisation-Electron Impact Ion Source for High Molecular Wdght Samples of Low Volatility. Z Naturforsch., B 1967,22,121-123. 

Many nonvolatile and thermally labile allelochemicals can be well separated by liquid chromatography (LC). Identification of the separated components on-line by mass spectrometry (MS) is of great value. Fused-silica LC columns of 0.22 mm ID packed with small-particle material are used in the described LC/MS system. The shape of the column end allows direct connection to a electron impact ion source of a magnetic sector mass spectrometer. Separations by LC are reported and LC/MS mass spectra are shown for monoterpenes, diterpene acids, phenolic acids and cardiac glycosides. The LC/MS system provides identification capability and high-efficiency chromatography with a universal detector. 

Ions are produced in a standard electron impact ion source (VG 70-70). The only modification necessary to obtain true electron impact spectra was to widen the LC inlet hole and uncover the other three inlet ports. 

The Bendix Corporation s (USA) time-of-flight mass spectrometer (ToF-MS) with a pulsed electron impact ion source was one of the first commercial non-magnetic sector mass spectrometers on the analytical market as described by Wiley in 1956.37... 

A low resolution mass spectrometer used for routine analysis by EPA Methods 8260 and 8270 consists of three main parts an ion source, a mass analyzer (both kept under vacuum conditions), and a detector. Although a variety of GC/MS instruments with different designs are available, the most common in the environmental laboratory are those with electron impact ion sources and quadrupole mass analyzers as they are best suited for the coupling with gas chromatography columns. These stable and reliable detectors with a relatively broad linear dynamic range became the workhorses of the environmental laboratory. 

Acidic pesticides - Teflon-coated electron impact ion source LC-MS 0.1 ppb [30]... 

An electron accelerated through a potential of v volts has an associated de Broglie wavelength of "v/loO/F (A) but, because of the poor energy resolution in most electron-impact ion sources, there is a spread in electron-beam energy. A spread of 0-5 volts in the visible region of the electromagnetic spectrum corresponds to a spread of 1200 A, not a... 

For example, little is known about the isotopic composition of formaldehyde in the atmosphere. Formaldehyde is a chemical intermediate in hydrocarbon oxidation. The carbon (8 C) and hydrogen (8D) isotopic composition of atmospheric formaldehyde is analyzed using continuous flow gas chromatography isotope ratio mass spectrometry." Isotope ratios were measured using GC-IRMS (Finnigan MAT 253 stable isotope ratio mass spectrometer, single-sector field with electron impact ion source and multiple ion collection) with a precision of 1.1 and 50%(lo ) for 8 C and 8D, respectively. The accuracy of the online continuous flow isotope technique was verified by calibrating three aliquots of the gas phase standard via the offline dual inlet IRMS technique. The concentration of formaldehyde in ambient air was determined on IRMS major ion peak areas (i.e., mass 44 for 8 C and mass 2 for 8D)." ... 

Figure 1.1. Schematic drawing of electron impact ion source...

Mass spectrometry is widely used for the qualitative analysis of unknowns samples, and in particular, for the identification and characterization of biological macromolecules. Recent decades have seen the introduction and optimization of the so-called soft ionization methods that provide intact, vapor-phase biomolecular ions for separation and detection. This chapter considers MS fundamentals, ionization methods, and applications to biological macromolecules. Conventional mass spectrometers used for low volatile molecular weight samples that are introduced in the vapor phase are called single-focusing mass spectrometers, and use an electron-impact ion source.1 Figure 15.1 shows a diagram of this type of instrument. 

At this point, it is necessary to stress that the brief introduction given above used positive ions as examples. However, it must be remembered that the same holds true for negative ions. Hence, an ionisation reaction such as that presented in equation (4) takes place simultaneously to that of equation (1) in an electron impact ion source. On a technical standpoint, negative ions can be observed as easily as positive ones a simple change in voltage potential within the source allows for directing these ions out of the source instead of their positive counterparts. 

Figure 2,31 Schematic diagram of an electron impact ion source (Figure used by kind permission of Jim Roe, Department of Chemistry, University of Washington, Seattle, USA).

---