DESIGN AND CHARACTERIZATION OF A HELIUM-DISCHARGE IONIZATION DETECTORFOR GAS-CHROMATOGRAPHY

A discharge ionization detector for gas chromatography was designed an d optimized for the analysis of inert gas. A wire-mesh suppression ele ctrode was placed between the discharge and collector electrodes so as to enhance the signal-to-noise ratio. The sensitivities obtained duri ng an atmospheric helium discharge were about 1000-times higher than t hose obtained under a reduced-pressure discharge. There was no signifi cant variation in the signal response when changing the applied potent ial to the suppression electrode. In contrast, when the size of the ho le in the suppression electrode was increased, the signal response was increased. These facts suggest that the eluent gas is ionized by phot ons or metastable helium atoms, but not by such charged particles as h elium ions or electrons. Under the optimum operating conditions, the n oise and background levels were 5X10(-13) A and 8X10(-9) A, respective ly. Detection limits of 0.2 - 2 pg/s were obtained depending on the de termined gases.