Ionization detector pulsed helium

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... 

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

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... 

The pulsed operation of the gas-filled detector illustrates the principles of basic radiation detection. Gases are used in radiation detectors since their ionized particles can travel more freely than those of a liquid or a solid. Typical gases used in detectors are argon and helium, although boron-triflouride is utilized when the detector is to be used to measure neutrons. Figure 5 shows a schematic diagram of a gas-filled chamber with a central electrode. 

Since the introduction of ECD, the Ni 3-ray radioactive electron source has remained unchanged, and considerable efforts have been made to develop nonradioactive alternatives. A new version of such a detector — the pulsed discharge electron capmre detector (PDECD) — employs a pulsed discharge in helium as the primary source of electron generation. A modified version of PDECD which makes use of methane as the dopant gas and of a sapphire and quartz insulation was used for detecting OCPs. The relatively low ionization potential of methane allows reduction... 

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