Varian 450-GC, User Manual

Page: 146 / 205

Detectors – Pulsed Discharge Helium Ionization Detector (PDHID)
Page: 296 User Manual 450-GC Varian, Inc.
Figure 48: Schematic of the PDHID Detector
HELIUM IONIZATION (PDHID)
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 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.