POTENTIOMETRIC GAS SENSOR FOR THE SELECTIVE DETERMINATION OF AZIDES

A potentiometric gas sensor offering a novel approach for rapid, simple, sensitive, and selective determination of inorganic azides is described. It consists of a flat-bottom glass electrode located behind a polypropylene porous membrane whereby a very thin film of 0.1 M NaN3-NaCl electrolyte solution is sandwiched between the electrode and the membrane. Hydrazoic acid released by acidification of azide test solutions diffuses through the membrane, rapidly equilibrates, and changes the pH of the electrolyte. The sensor exhibits a rapid linear response for a logarithmic concentration of 10(-1)-10(-4) M N3- with a cationic slope of 58.8 mV (concentration decade)-1. The performance characteristics of the sensor with regard to the origin of response, response time, influence of membrane type, selectivity, electrolyte osmolality, effect of pH, effect of temperature, and potential stability have been systematically examined. The sensor was also evaluated in the presence of various volatile weak acid releasing salts such as nitrite, sulfite, sulfide, carbonate, cyanide, thiocyanate, cyanate, acetate, and formate. As low as 0.8-mu-g mL-1 of N3- is determined in the presence of many interferents, after a prior treatment with H2O2, with an average recovery of 98% (standard deviation 0.4%). The sensor displays significant advantages over most of the previously suggested instrumental and conventional methods.