Analytical Instrument Documents

What is a Gas Chromatograph – Mass Spectrometer (GC-MS)? Learn more in this guidebook written by our experts.

In this work, we compare sensitivity levels when using the combination EI/FI and EI/PI ion sources when He and N2 are used as the GC carrier gas.

Mass spectrometers are commonly combined with separation devices such as gas chromatographs (GC) and liquid chromatographs (LC). The GC or LC separates the components in a mixture, and the components are introduced, one by one, into the mass spectrometer. MS/MS is an analogous technique where the first-stage separation device is another mass spectrometer.

Accurate mass measurements are frequently used to determine the elemental composition for molecular and fragment ions. These measurements are normally obtained by acquiring a high resolution mass spectrum so that the masses are measured for a single species and not measured for unresolved or partially resolved peaks.

What does a mass spectrometer do? What are mass spectrometers used for? What does the mass tell us? How does a mass spectrometer work?

Several different definitions of resolution are used in mass spectrometry. It is useful to understand the distinctions between the different definitions to understand the characteristics of different mass spectrometers.

All mass spectrometers combine ion formation, mass analysis, and ion detection. This discussion is concerned with how various mass analyzers are used to separate ions according to their massto- charge ratio. Each mass analyzer has its own special characteristics and applications and its own benefits and limitations. The choice of mass analyzer should be based upon the application, cost, and performance desired. There is no ideal mass analyzer that is good for all applications. For an excellent and more complete discussion of mass analyzers, see "The Ideal Mass Analyzer: Fact or Fiction?" (Curt Brunnee, Int. J. Mass Spectrom. Ion Proc. 76 (1987), 125-237.

A mass spectrometer works by using magnetic and electric fields to exert forces on charged particles (ions) in a vacuum. Therefore, a compound must be charged or ionized to be analyzed by a mass spectrometer. Furthermore, the ions must be introduced in the gas phase into the vacuum system of the mass spectrometer. This is easily done for gaseous or heat-volatile samples. However, many (thermally labile) analytes decompose upon heating. These kinds of samples require either desorption or desolvation methods if they are to be analyzed by mass spectrometry. Although ionization and desorption/desolvation are usually separate processes, the term "ionization method" is commonly used to refer to both ionization and desorption (or desolvation) methods. The choice of ionization method depends on the nature of the sample and the type of information required from the analysis. So-called 'soft ionization' methods such as field desorption and electrospray ionization tend to produce mass spectra with little or no fragment-ion content.

Double-focusing magnetic sector mass spectrometers provide high sensitivity, high resolution, and a reproducibility that is unmatched in any other kind of mass analyzer.