RESPONSE FUNCTION AND ANALYTICAL PARAMETERS OF NITRITE-SELECTIVE OPTODE MEMBRANES IN ABSORBENCY AND FLUORESCENCE MODE

Four different nitrite-selective optode membranes were studied. Each m embrane consisted of a nitrite-selective ligand and four different H+- selective chromoionophores dissolved in a plasticized poly(vinyl chlor ide) bulk medium. The membranes' analytical parameters differ with res pect to optical spectra, dynamic range and detection limit. The unique features of each membrane are discussed and the versatility of the op tical sensors based on the membranes is evaluated. The response functi ons of the optical sensors, derived from the changes in the absorbance and/or fluorescence of the membranes with varying nitrite concentrati on, are described by a theoretical model based on coextraction equilib ria. The dynamic range of the sensors extended from 0.5 to 5000 mg l(- 1) nitrite with a detection limit of 0.24 mg l(-1). The response time, tau(95), of the membranes placed in a continuous flow measuring cell was 1.2 min when changing from 0.5 mg l(-1) nitrite to 0.05 mg l(-1), and 3.6 min in the opposite direction. The selectivity coefficients de termined by the separate solution method were: 10(-3.3) for nitrate, 1 0(-3.7) for chloride, 10(-3.0) for bromide, 10(-3.8) for sulphate, and 10(-5.0) for phosphate. Various applications of these optode membrane s are discussed. (C) 1997 Elsevier Science B.V.