ON-COLUMN BROMINE-SELECTIVE AND CHLORINE-SELECTIVE DETECTION FOR CAPILLARY GAS-CHROMATOGRAPHY USING A RADIO-FREQUENCY PLASMA

A 350-kHz rf plasma sustained inside the end of a 0.25- or 0.32-mm-i.d. fused-silica GC column was evaluated for element-selective detection of brominated and chlorinated compounds separated by gas chromatography. Due to the small volume of the plasma cell, dilution of the GC effluent with make-up gas was unnecessary and a stable 25-W plasma was maintained in only 1.5-5 mL/min GC carrier gas. With the plasma sustained in pure helium, carbon formed from eluting material was deposited in the plasma region causing serious peak tailing and loss of sample. This was avoided by doping the GC carrier gas with traces of oxygen. With the 350-kHz rf plasma sustained on-column, detection limits for bromine and chlorine were improved by a factor of 50 to 0.9 and 1.1 pg/s, respectively. For both bromine and chlorine, element-to-carbon selectivities approaching 10(3):1 and detector linearity over at least 3 orders of magnitude were obtained. The on-column detection system has been applied to a screening for halogenated compounds in snow from Antarctica and in drinking water produced offshore.