Inficon HAPSITE Smart, Руководство по эксплуатации

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HAPSITE Smart Operating Manual
The inlet flow from the membrane isolation valve is brought directly to the ionizer .
Within the ionizer, the component introduced from the inlet flow is subjected to a
bombardment of electrons which are boiled off the hot
filament . Collisions with the
energetic electrons remove one electron from some of the gas molecules, leaving
them with a net positive charge. This process is termed
ionization . Other gas
molecules are fractured into smaller molecules, some of which are also ionized.
The remaining stream of gas continues out the far side of the ion volume and is
pumped away by the vacuum pump system.
The ionized molecules, or ions, are driven from the ionizer toward the mass
selector by the different voltages on the ion volume and the focusing plates which
follow. As the ions move through the holes in these plates, the ions are formed into
a nearly parallel beam of mixed ions of nearly the same energy.
The mass selector (or mass filter) is a quadrupole analyzer. The quadrupole
analyzer is comprised of four parallel rods, mounted with precise alignment and
spacing. Opposite rods are electrically connected together. The two pairs of rods
are connected to a radio frequency (RF) voltage 180
o
out of phase with each other.
In addition, the two pairs of rods have a direct current (DC) voltage applied to them;
positive on one pair, negative on the other.
The ion beam is directed down the center of the array of rods. At any specific
combination of RF and DC fields, some ions are light enough to oscillate
harmonically with the RF field, picking up energy and increasing speed until the
ions impact one of the rods and are neutralized. Much heavier ions, moving more
slowly, cannot respond to the RF field. The heavier ions are dragged from the
center by the DC field, landing on one of the rods. Once on the rod, the heavier ion
is neutralized. At a specific combination of RF and DC fields, ions of a specific
mass will be able to transit the rod structure and emerge at the exit end to be
detected.
When the ions emerge from the mass selector, the ions are directed to the detector.
The active element of the detector is an electron multiplier. The electron multiplier
responds to the arrival of each individual ion with a cascade of electrons, each of
which generates more electrons. The result is a small burst of electrical current in
response to each ion emerging from the mass selector. The signal from the
electron multiplier is connected to the electronic amplifier and data-handling
system outside the vacuum.
In order to determine the constituents of the gas mixture, the ratio of RF to DC field
strengths is varied (swept) to permit progressively heavier ions to transit the mass
selector. The sweep, or scan, over the full range of masses (from 1 to 300 AMU)
only takes about 100 milliseconds; the sweep is usually repeated many times to
statistically improve the quality of the data. This produces the mass spectrum, a
plot of the partial pressure (or population or intensity or amplitude) of each mass.
The mass spectrum is compared with a library of mass spectra characteristic of
many individual compounds, and the HAPSITE reports the compounds which
match the observed spectrum.