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Transpector MPH Operating Manual
Ionization Probability
The ionization probability for a chemical substance is the ratio of the total
ion current (at all masses) produced from a given partial pressure of that
substance, to the total ion current produced from nitrogen at the same
partial pressure.
Isotope
The atom is composed of nucleus protons and neutrons surrounded by an
electron cloud. The chemical properties of an element are determined by
the number and arrangement of electrons (with -1 charge) in an atom. The
number of electrons in a neutral atom in turn depends on the number of
protons (with +1 charge) within the nucleus of that atom. Atomic nuclei
also contain neutrons which, being uncharged, do not affect the chemistry
of an element. Protons and neutrons have approximately the same mass,
which is approximately 1,800 times the mass of an electron. All atoms of a
given element have the same number of protons but not necessarily the
same number of neutrons. Atoms of the same element which have a
different number of neutrons are called isotopes. See also Natural
Abundance.
Linearity
Linearity is the mathematical relationship between an ion current and the
total or partial pressure giving rise to that current. A mass spectrometer is
said to have good linearity when the ion current is proportional to the
pressure over a specified pressure range within a specified tolerance.
Typically (but not always), the ion current will be linear with pressure at the
low end of an instrument’s pressure range. At some pressure near the
high pressure end of an instrument’s range, the ion current will be less
than proportional to the pressure.
Mass to Charge Ratio
The mass to charge ratio is ratio of the mass of an ion to its charge,
usually expressed in atomic mass units per unit electron charge.
Mass Filter
The mass filter is that part of the mass spectrometer which separates a
beam of ions by their mass to charge ratios.
Mass Spectrometer
A mass spectrometer is an instrument which ionizes a gas sample,
separates the resulting beam of ions by mass to charge ratio, and detects
the filtered ions as an electrical signal.
Mass Spectrum
A mass spectrum is a record of ion current as a function of mass to charge
ratio obtained with a mass spectrometer. The spectrum can be presented
as a graph with mass to charge ratio on the X-axis and ion current on the
Y-axis, or as a tabular listing of ion currents and the associated mass to
charge ratios.
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