A Novel Detector for Gas Chromatography Based on UV Laser-Produced Microplasmas

Abstract

The use of UV laser-produced microplasmas for the detection of analyte molecules in the effluent gases of a gas chromatograph is described. The microplasmas are formed when a carbon-containing analyte is present in the carrier gas flow but not in the carrier gas alone. The microplasmas are produced by using the 193-nm output of the ArF excimer laser, with only modest pulse energies (10 mJ) required. Three means for detecting the presence of the microplasmas have been effected and are compared: optogalvanic (plasma electron) detection, photoacoustic (blast wave) detection, and photometric (plasma emission) detection, particularly of electronically excited carbon atoms at 248 nm. The relative responses of these three techniques have been determined for microliter injection of acetylene into the helium flow. Present limits for acetylene with the use of the optogalvanic, photoacoustic, and photometric techniques are 500, 500, and 10 ng, respectively. Optimization of these techniques is expected to improve the detection limits by 2–4 orders of magnitude. The virtues of this detector include the fact that it requires no flame and that it is sensitive to carbon-containing species such as CO and CO2.