Characteristic responses of an atmospheric pressure DC micro-plasma detector for gas chromatography to organic functional groups

A gas chromatographic detector using direct current micro-plasma discharged a distance of less than 50 μm under helium at atmospheric pressure is described. The micro-plasma device was assembled on glass substrates; the volume of the plasma region was only 0.58 nL. Very low power consumption (15 mW) and only carrier helium flow were needed to maintain micro-plasma stability. Organic compounds with various functional groups were chromatographically separated and fed into the micro-plasma. Fluctuations in plasma current were detected as the sample passed through the micro-plasma. All non-halogen organics showed positive peaks, while simple alkyl halides showed negative peaks. Compounds with both aromatic and halogen groups exhibited hybrid peak shapes, consisting of both positive and negative peaks. The detection limits (3σ) ranged from 24.5 pg for m-xylene to 756 pg for 1,2-dichloroethane, depending on differences in ionization and electron-capture efficiency.