VICI D-4-I-TQ-R - Manual (Page 6)

2
Helium Ionization (PDHID) Mode
The PDHID is essentially non-destructive (0.01 - 0.1% ionization) and highly
sensitive. The response to organic compounds is linear over five orders of
magnitude with minimum detectable quantities (MDQs) in the low or sub
picogram range. The response to fixed gases is positive (the standing
current increases), with MDQs in the low ppb range.
The PDHID response is universal except for neon, which has an ionization
potential of 21.56 eV. Since this potential is close to the energy of the He*
metastable (19.8 eV) but greater than the photon energy from the He
2
continuum, neon exhibits a low ionization efficiency and low detector
response.
Photoionization (PDPID) Mode
Changing the discharge gas from pure helium to helium doped with argon,
krypton, or xenon changes the discharge emission profile, resulting in
resonance atomic and diatomic emissions of the rare gas added. Response
is limited to sample compounds with ionization potentials less than or equal
to the dopant gas emission energy. In this configuration, the detector is
essentially functioning as a specific photoionization detector for selective
determination of aliphatics, aromatics, and amines, as well as other species.
Since there is no lamp or window, sensitivity will not change with time.
Safety Notes and Information
CAUTION: During normal operation, the detector pro-
duces ultraviolet energy (UVA, UVB), some of which may
be emitted. Do not watch the arc without eye protection.
Symbols
HIGH VOLTAGE
Voltages presenting the risk of electric shock are present in
several places in the equipment. Avoid contact with hazard-
ous live parts. Do not probe into openings or attempt to
defeat safety mechanisms.
HOT SURFACE
The surface of the detector body may be hot while in opera-
tion (possibly in excess of 250°C). Caution should be
observed.
ATTENTION
Refer to the manual.
PROTECTIVE EARTH
This internal connection provides protection against electric
shock from mains voltages and should not be removed.
Introduction