Helium ionization

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... 

Figure 5.14 The helium ionization yield for the ion being left in the He+(2s) and He+(2p) excited states as a function of the time delay between the initial XUV pump pulse and the IR probe pulse. The oscillations are due to breathing between different doubly excited states (resonances).

This method is well suited for the calibration of a monochromator.) With known photon energy and helium ionization energy , = 24.5874 eV [Moo71], the... 

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. 

F. Andrawes and S. Greenhouse, Applications of the helium ionization detector in trace analysis, J. Chromatogr. Sci., 26 153-159 (1988). 

Helium ionization (HID) photoionization He carrier gas ionized Universal, but 25... 

The pulsed discharge electron capture detector is an extension of the previously discussed pulsed discharge helium ionization detector, a... 

The sensor consists of two sections the upper section where the discharge takes place has a small diameter and the lower section where the column eluent is sensed and the electron capturing occurs has a wider diameter. As with the pulsed discharge helium ionization detector, the potential across the discharge electrodes is pulsed at about 3 kHz with a discharge pulse width of about 45 psec for... 

It will be interesting to see how the various detecting systems based on the different helium ionization processes that were discussed in the previous chapter fare commercially over the next few years. 

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. 

Thiatriazinyl radicals have been generated in the gas phase and studied by helium ionization photoclectron spectroscopy. Ionization potential and hyperfine coupling constant data for these radical systems have been analyzed in relation to the results of MINDO calculations and their electronic structure. 

Andrawes F.F. and Gibson E.K. (1982) Direct analysis of some aroma compounds by gas chromatography with helium ionization detection. J. High Res. Chromatogr. Chromatogr. Commun. 5, 265-6. 

All ionization detectors have the same base body. They are all miniaturized. They are not universal with the exception of the helium ionization detector. 

FIGURE 4.4 Helium ionization mode (by courtesy of Vici). 

Abbreviations GC, Gas Chromatography IRMS, Isotope Ratio Mass Spectrometry ECD, Electron Capture Detector FID, Flame Ionization Detector TCD, Thermal Conductivity Detector MS, Mass Spectrometry PDHID, Pulsed-Discharge Helium Ionization Detector mol. sieve, Molecular Sieve HP, Hewlett-Packard PE, Perkin-Elmer. 

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. 

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