Helium Ionisation Detector (HID):

A few of the characteristics of this detector are given below.

i)          Universal

ii)        Photo-ionization

iii)       Sensitive to fractional categories per million

The helium ionisation detector is a universal detector except of course, it will not sense helium. The mixture of the tritium beta radiation and high field gradient (4000 volts per cm) increase the helium to a metastable state along with an ionisation potential of 19.8 eV. All solutes having a lower ionisation potential will be ionized providing rise to a positive signal. The HID was established for the ultratrace analysis of permanent gases.