BACKGROUND CORRECTION DEVICE FOR ENHANCED ELEMENT-SELECTIVE GAS-CHROMATOGRAPHIC DETECTION BY ATOMIC-EMISSION SPECTROSCOPY

A two-channel optical device has been used to enhance the selectivity of sulfur detection based on emission from a radio-frequency helium plasma coupled to a gas chromatograph (GC). A wedge prism was used to split collimated emission from the plasma into two components with an angular separation of nine degrees. The two beams were then transmitted through a narrow-band interference filter at center wavelengths of 918.0 and 921.3 nm. Background radiation at 918.0 nm was scaled and subtracted from the combined signal and background radiation at 921.3 nm to give a net sulfur emission signal that was insensitive to the passage of sulfur-free species through the plasma. The performance of the device was characterized in use with a radio-frequency plasma attached to a comprehensive SFE/GC system as well as to a conventional capillary gas chromatograph. The detection limit and selectivity for the SFE/GC system were 17 pg s-1 and 23,000 respectively. The detection limit and selectivity for the conventional GC were 0.2 pg s-1 and 12,000, respectively.