CONTINUOUS MONITORING OF GAS-PHASE SPECIES AT TRACE LEVELS WITH ELECTROCHEMICAL DETECTORS .2. DETECTION OF CHLORINE AND HYDROGEN-CHLORIDE

A detection system suitable for the continuous and simultaneous measurement of gas-phase chlorine and hydrogen chloride in the low parts per billion (10(9)) by volume (ppbv) range is described. Both gases are trapped through the walls of a microporous polypropylene tube into an appropriate flowing recipient buffer. The buffer then flows through two electrochemical detectors placed in series downstream from the sampling tube. Chloride ions from gas-phase hydrogen chloride are detected potentiometrically with an Ag/AgCl working electrode. Chlorine is detected biamperometrically (at 0.1 V) via its oxidation of added iodide ions to form triiodide. In a continuous-flow measurement mode, detection of chlorine and hydrogen chloride at levels as low as 0.75 and 2.1 ppbv, respectively, is possible. Use of a 2-min stopped-flow/flow-injection arrangement results in a three-fold improvement in detection limits. The selectivity of each detector with respect to carbon dioxide, sulfur dioxide, nitrogen dioxide and hydrogen sulfide is also examined.