Inficon Transpector MPH - Applications Guide; How to Interpret the Result; Qualitative Interpretation of Mass Spectra

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Transpector MPH Operating Manual
Chapter 4
Applications Guide
4.1 How to Interpret the Result
This chapter discusses how to interpret Transpector MPH measurements:
 Section 4.1.1, Qualitative Interpretation of Mass Spectra, on page 4-1, explains
how to determine which substances are present in the gas sample being
analyzed.
 Section 4.1.2, Quantitative Interpretation of Mass Spectra (Calculating Partial
Pressures), on page 4-8, shows how to estimate how much of each substance
is present.
 Section 4.1.3, Additional Information for Interpreting Mass Spectra, on page
4-14, provides additional information that may help you interpret mass spectra.
FabGuard software includes routines which serve as aids in the interpretation of
spectra and the calculation of partial pressures and relative concentrations.
For a discussion of how Transpector MPH produces measurements, refer to
Chapter 3, How The Instrument Works.
4.1.1 Qualitative Interpretation of Mass Spectra
The basic graphical output of a Transpector MPH is the mass spectrum. A mass
spectrum is a plot of ion intensity as a function of ion mass-to-charge ratio. Each
chemical substance has a characteristic mass spectrum. Different instruments will
give slightly different spectra for the same substance. The particular characteristics
of the ionizer, mass filter, and detector, not to mention the manner in which the
sample is introduced into the mass spectrometer, all influence the spectrum that is
produced.
Rarely will a mass spectrum be obtained for a pure substance. Most of the time
(especially for residual gas analyzers), the spectrum obtained will be a composite
of the individual substances which together comprise the actual sample present.
See Figure 4-1.