Gas Chromatography Detectors - Ionization Detectors > The Pulsed Helium Discharge Detector > Page 68


The pulsed helium discharge detector contains two discrete sections. The upper section consists of a tube 1.6 mm I.D. (where the discharge takes place) and the lower section, a tube 3 mm I.D. (where reaction with metastable helium atoms and photons takes place). Helium make–up gas enters the top of the sensor and passes into the discharge section. A potential (about 20 V) applied across the discharge electrodes is pulsed at about 3 kHz with a discharge pulse-width of about 45 ms for optimum performance. The discharge produces electrons and high energy photons (that can also produce electrons), and probably some metastable helium atoms.



Column; J & W DB–1701, 10 m x 0.05 mm, film thickness 0.05 mm; Flow rate 20 ml/min. Sample split 1:150;1, benzene; 2, toluene; 3, ethylbenzene; 4, m and p xylene; 5, o-xylene


Figure 37 The Separation of Some Aromatic Hydrocarbons Monitored by the Pulsed Helium Discharge Detector