CAPILLARY GAS-CHROMATOGRAPHY COUPLED WITH MICROPLASMA MASS-SPECTROMETRY - IMPROVED ION-SOURCE DESIGN COMPATIBLE WITH BENCH-TOP MASS-SPECTROMETRIC INSTRUMENTATION

Capillary gas chromatography was performed with mass spectrometric det ection using a novel microplasma ion source for operation in an elemen t-selective mode, The ion source was a 350 kHz radio frequency helium plasma, which was sustained inside the 4 cm end of a 0.32 mm i.d. fuse d silica capillary column, and located inside the high vacuum chamber of the quadrupole mass spectrometer. Due to the low volume of the ion source, a stable low pressure discharge was produced utilizing only th e 2.25 mt min(-1) of GC carrier gas (helium) for plasma support, Small amounts of oxygen (0.1-0.2% v/v) were added to the plasma gas in orde r to prevent carbon deposits and to enhance signal-to-noise ratios. Ch lorine and bromine were selectively detected at the 5-20 pg s(-1) leve l (S/N = 2), and both produced a response that was linear within 3 ord ers of magnitude.