MICROPLASMA MASS-SPECTROMETRIC DETECTION IN CAPILLARY GAS-CHROMATOGRAPHY

A simple and miniaturized 350-kHz helium discharge for plasma mass spe ctrometric detection in gas chromatography (GC) has been developed, Th e plasma was sustained at low pressure within the end of the capillary GC column (0.32-mm i.d.) inside the ion source housing of a quadrupol e mass spectrometer. This allowed direct introduction of ions from the plasma to the mass analyzer using only a repeller and electrostatic l enses to focus the ions. The plasma was sustained in only 25 mL min(-1 ) of helium, which was accepted by the mass spectrometer vacuum system , This low gas flow also sewed to enhance the energy density of the di scharge and to produce a narrow spray of ions toward the mass analyzer . Due to the miniaturized nature of the plasma, it was operated at a l ow power level (2.0 W), and traces of oxygen were added to avoid depos ition of carbon, With this new concept for GC plasma mass spectrometri c detection, chlorine was successfully monitored down to the 2.2 pg s( -1) level without interference from elements like C, S, P, O, F, and N .