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Transpector XPR 3+ Operating Manual
Chapter 4
Applications Guide
4.1 How to Interpret the Result
This section explains how to interpret the measurements Transpector XPR 3+
produces. It is divided into three main parts:
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 4-9, shows how to estimate how much of each substance
is present.
Section 4.1.3, Additional Information for Interpreting Mass Spectra, on page
4-15, provides additional information that may help you interpret mass spectra.
For a discussion of how Transpector XPR 3+ produces its measurements, refer to
Chapter 3, How The Instrument Works.
4.1.1 Qualitative Interpretation of Mass Spectra
The basic graphical output of a residual gas analyzer is the mass spectrum. A mass
spectrum is a pattern of peaks on 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.)
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