Electron Ionization Sources: The Basics - - Spectroscopy
 Home   Mass Spectrometry   ICP-MS   Infrared   FT-IR   UV-Vis   Raman   NMR   X-Ray   Fluorescence  
Issue Archive
Special Issues
The Application Notebook
Current Issue
Submission Guidelines
Digital Edition
Subscribe to the Digital Edition
The Wavelength
Subcribe to The Wavelength
Subscribe to the MS E-news
Market Profiles
Information for Authors
Advertiser services
Contact Us
Atomic Perspectives
Chemometrics in Spectroscopy
Focus on Quality
Laser and Optics Interface
Mass Spectrometry Forum
The Baseline
Molecular Spectroscopy Workbench

Electron Ionization Sources: The Basics

Volume 21, Issue 7, pp. 14-18

The sensitivity of a mass spectrometer (the source combined with the remainder of the instrument, but sometimes also the source itself) is defined strictly in units of C/μg, where C represents the charge in coulombs carried by ions that can be created from 1 μg of sample introduced to the source. The sensitivity of any MS measurement is predicated first upon instrument sensitivity (including factors such as source performance, mass analyzer transmission, and ion detection efficiency), but also expands to include sample preparation, signal-to-noise discrimination, and matrix effects in real samples. The central position of source performance in this scheme should be clear. For EI sources, source design and operational details directly affect source performance. It is useful then to broadly consider the 50-year history of the EI source in terms of sensitivity, and its optimization, but also to include all the other factors that go into the design and construction of an ion source.

We begin with the essential elements of the EI source. Essential components of an EI source assembled into the basic layout can be found in schematics in introductory texts or manufacturer's literature on the web. Often it seems that short shrift is given to the EI source, and details of design and optimization are overlooked in the fact that the EI source is so common. Lack of current research literature on the design of the EI source reflects the long history of successful development of this source for organic analysis, the tendency for design studies to be completed now in conjunction with instrument manufacture (and therefore to be proprietary), and the attention given to new ionization methods. However, more specialized applications of the EI source often require revisiting these fundamental design parameters; examples of these applications include portable instruments and instruments for analysis in extreme environments. Importantly, an appreciation of the factors considered in the design of the EI source, the balances reached in accord with the transfer of sample molecules into the source, and the transfer of ions out of it informs our designs and evaluations of other ionization sources. In this column, we begin a brief overview of some of these factors and balances; then in the next column, we revisit some of the "older" scientific literature and hopefully enlighten the understanding of source design for mass spectrometers.

Rate This Article
Your original vote has been tallied and is included in the ratings results.
View our top pages
Average rating for this page is: 4.41
Headlines from LCGC North America and Chromatography Online
Detecting Ignitable Liquids with GC–MS
Chromatography for Keeping Astronauts Safe
GC–MS Analysis of Blowflies to Detect Methamphetamine
Digital Microfluidics Coupled to Miniature MS
Antimicrobial Exposure of Expectant Mothers
Source: Spectroscopy,
Click here