Azide ion is a toxic and potentially deadly species as it reduces oxygen consumption by body cells causing harmful effect on lung, heart, and brain. On the other hand, azide is used in explosive detonators, electrical discharge tubes, anticorrosion solutions, production of foam rubber, hospitals and laboratories preservatives, agricultural pest control, and automobile airbags. Conventional methods for determining inorganic azides are based on redox titrimetry [1 -4], argentometry [5,6], gasometry [7,8] and spectrophotometry [9]. Most of these methods are applicable over a high and narrow range of concentrations and suffer from severe interference by many common ions.Amperometric sensors have been suggested for azide measurements. The decrease in the differentiation of oxygen level as a function of azide due to inhibition of catalase , laccase and tyrosinase enzymes in bioactive layer of biosensors have been described [10,11]. These sensors have a limited narrow measurement range (0.25 to 3.0 Â 10 À4 mol L
À1) and suffer from interferences by other inhibitors (e.g., acetate, fluoride). Although potentiometric sensors are attractive technique for the determination of many anions, due to simplicity, rapidity, selectivity, accuracy and automation feasibility, little is known about the use of these devices for determination of azides. The commercially available solid state chloride and fluoride ion selective electrodes have been utilized for determining azides. Direct potentiometric titration of azide ion with silver nitrate has been monitored with silver chloride membrane electrode [12].The fluoride electrode was also used to follow up the kinetic release of fluoride ion as a function of azide concentration (10 À2 À 10 À4 mol L À1 ) upon reaction with 1-fluoro-2,4-dinitrobenzene [13]. Significant interferences by halides, pseudo halides, amines, thiols and other species have been reported with both methods.A potentiometric gas sensor consisting of a glass electrode located immediately behind a gas permeable membrane wherever a very thin film of internal azide electrolyte is sandwiched between this electrode and the gas permeable membrane has been suggested. Upon acidification of the azide test solution, hydrazoic acid is liberated, which diffuses and sensed by the glass electrode [14]. An ammonia sensitive electrode with a PTFE semi permeable membrane has been similarly used [15]. Poly(vinyl chloride) matrix membrane sensors for manual and flow injection determination of metal azides have been developed using metalbathophenanthroline-azide and metal-tetraazaporphyrin ionophores [16,17].Porphyrins are iso-electronic to phthalocyanines and both classes are able to form stable metal complexes suitable for use as ionophores in anion selective sensors. The conjugated 438
