DETECTION OF ARGON BY PENNING IONIZATION AND COMPETITIVE ABSORPTION USING A SENSITIZED PHOTOIONIZATION DETECTOR

A novel application of a commercial photoionization detector for the q uantification of argon is described and applied to the headspace analy sis of water. Using an argon lamp as the excitation source, argon is m easured indirectly by its effect on an ionizable gas present in the de tection cell. Nitric oxide is added to the effluent of a gas chromatog raphy column, resulting in an elevated background ion current in a pho toionization detector. By varying the amount of nitric oxide added to the detection cell, two modes of operation were demonstrated: a compet itive absorbance mode in which a high background of nitric oxide photo ionization was reduced in response to the presence of argon and a Penn ing ionization mode in which a relatively lower background of nitric o xide photoionization was enhanced in response to the presence of argon . Optimized Penning ionization detection with a nitric oxide concentra tion at similar to 940 ppmv was used to analyze air and the headspace of water samples. The limit of detection was determined to be 14 pmol of Ar s(-1).