The Helium Ionization Detector HID

Universal detector (everything except neon) nondestructive mass-flow detector a little less sensitive than FID for FID-active compounds, and with less dynamic range than the FID. 

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The helium ionization detector (HID) is probably the least used of the ionization detectors. It is a universal and ultra sensitive detector with a reputation for unreliability and... 

The helium ionization detector (HID) is a sensitive universal detector. In the detector, Ti3H2 or Sc3H3 is used as an ionization source of helium. Helium is ionized to the metastable state and possesses an ionization potential of 19.8 eV. As metastable helium has a higher ionization potential than most species except for neon, it will be able to transfer its excitation energy to all other atoms. As other species enter the ionization field the metastable helium will transfer its excitation energy to other species of lower ionization potential, and an increase in ionization will be measured over the standing current. 

At the temperatures and pressures generally used in gas chromatography the common carrier gases employed behave as perfect insulators. In the absence of conduction by the gas molecules themselves, the increased conductivity due to the presence of very few charged species is easily measured, providing the low sample detection limits characteristic of ionization based detectors [259]. Examples of ionization detectors in current use include the flame ionization detector (FID), thermionic ionization detector (TID), photoionization detector (PID), the electron-capture detector (ECD), and the helium ionization detector (HID). Each detector employs a different method of ion production, but in all cases the quantitative basis of detector operation corresponds to the fluctuations of an ion current in the presence of organic vapors. 

The helium ionization detector (HID) is often used for the detection of inert gases. 

Detectors commonly used in GC and specified in the USPP include FID, alkali FID (NPD, TD), BCD, and TCD. A description of these detectors, including their operational principles and relative performance, was presented in a previous volume of this encyclopedia. Various other useful detectors for GC include photoionization (PID), flame photometric (FPD), electrolytic conductivity (BLCD), redox (RCD) and sulfur chemiluminescence (SCD), and helium ionization (HID).[4 1 Table 1 summarizes some of the features of detectors used in GC. 

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