Design and characterization of a helium-discharge ionization detector for gas chromatography

A discharge ionization detector for gas chromatography was designed and optimized for the analysis of inert gas. A wire-mesh suppression electrode was placed between the discharge and collector electrodes so as to enhance the signal-to-noise ratio. The sensitivities obtained during an atmospheric helium discharge were about 1000-times higher than those obtained under a reduced-pressure discharge. There was no significant variation in the signal response when changing the applied potential to the suppression electrode. In contrast, when the size of the hole in the suppression electrode was increased, the signal response was increased. These facts suggest that the eluent gas is ionized by photons or metastable helium atoms, but not by such charged particles as helium ions or electrons. Under the optimum operating conditions, the noise and background levels were 5X10(-13) A and 8X10(-9) A, respectively. Detection limits of 0.2 - 2 pg/s were obtained depending on the determined gases.