Helium discharge ionization detector

The metastable atoms that must be produced in the argon and helium detectors need not necessarily be generated from electrons induced by radioactive decay. Electrons can be generated by electric discharge or photometrically, which can then be accelerated in an inert gas atmosphere under an appropriate electrical potential to produce metastable atoms. This procedure is the basis of a highly sensitive helium detector that is depicted on the left-hand side of Fig. 1. The detector does not depend solely on metastable helium atoms for ionization and, for this reason, is called the helium discharge ionization detector (HDID). 

The helium discharge ionization detector has a high sensitivity toward the permanent gases and has been used very successfirUy for the analysis of trace components in idtrapure gases. It woidd appear that the detector response is Unear over at least two, and possibly three, orders of magnitude, with a response index probably lying between... 

Another unique application is shown in Fig. 7-7. Here a 100 ppb amount of methane could be determined by using a special type of detector, the helium Discharge Ionization Detector (DID). This type of detector, which is known to be very sensitive, made it possible to reach detection limits of ppb levels of permanent gases. 

Fig.l The discharge ionization detector (courtesy of GOW-M AC Instruments) and the pulsed helium discharge detector (courtesy of Valeo Instruments). 

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... 

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. 

Dojahn JG, Wentworth WE, Deming SN, and Stearns SD (2001) Determination of percent composition of a mixture analyzed by gas chromatography. Comparison of a helium pulsed-discharge photoionization detector with a flame ionization detector. Journal of Chromatography A 917 187-204. 

One drawback of the ECD is the necessity to use a radioactive source which may require a license or at least regular radiological testing. A new innovation is an ECD operated with a pulsed discharge (FDD) so that it does not require a radioactive source [25]. This detector is commercially available and can also be operated as a helium ionization detector under different conditions. 

The base current ranges from 1 x 10 to 5 X 10 A, the noise level is about 1.2 x 10 A, and the ionization efficiency is about 0.07%. It is claimed to be about 10 times more sensitive than the flame ionization detector and to have a linear dynamic range of 10. The pulsed helium discharge detector appears to be an attractive alternative to the flame ionization detector and would eliminate the need for three different gas supplies. It does, however, require equipment to provide specially purified helium, which diminishes the advantage of using a single gas. 

Wentworth, W.E. Vasnin, S.V. Stearns, S.D. Meyer, C.J. Pulsed discharge helium ionization detector. Chromatographia 1992, 34, 219. 

Pulse Discharge Helium Ionization Detector (PDHID)... 

PDHID Pulse discharge helium ionization detector... 

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