APPLICATION OF A LASER INTRACAVITY ABSORPTION DETECTOR TO GAS CHROMATOGRAPHY OF TRACE ORGANIC POLLUTANTS IN WATER.

A helium-neon laser operating simultaneously at 3. 39 mu m (infrared) and 0. 63 mu m (visible) has been used as a selective detector for hydrocarbons in the effluent of a gas chromatograph. The infrared and visible laser transitions originate at the same energy level and are competitive. When a hydrocarbon enters the laser's resonant cavity, the 3. 39 mu m energy is absorbed due to the C-H stretching vibration and the visible emission is enhanced. The visible laser emission is monitored with a photodiode as a quantitative measure of the concentration of the absorbing molecule. The detector's selectivity for hydrocarbons is modified by various substituents. The detector responds to aliphatic and aromatic hydrocarbons with aliphatic side chains, except for those substituted with halogens. The HeNe laser intracavity absorption detector may be used without prior separation in some cases. This detector operates with nitrogen carrier gas without sacrifice of sensitivity. Refs.