Abstract: Dithizone immobilized on XAD-4 resin was studied as the sensing element of an optical sensor for Pb using a flow-cell. Measurements were made using two different procedures. In 'kinetic analysis', the standard Pb solution was allowed to flow at a constant rate and the analytical signal was recorded as a function of time, whereas in the 'concentration procedure' only the initial and final values of reflectance were recorded, the light path being blocked during the addition of Pb solution and the regeneration of the reagent phase to avoid any photodegradation. Measurements were expressed as the relative reflectance, defined as the reflectance of the Pb complex minus that of the immobilized dithiozone alone. Lead in solution was determined from 0.3 to 10 µM with a detection limit of 10 nM. The sensor response was reproducible and could be regenerated using 10 mM HCl followed by citate - hydroxylamine solution The method may be applied in flow injection analysis and online analysis, and is suitable for most environmental analyzes, including drinking water.

Abstract: The Alizarin Fluorine Blue method for the determination of fluoride has been adapted for use with optical fibers. The reagent was immobilized on a polymer matrix, Amberlite XAD-2, and the reflectance of this reagent phase was measured as a function of fluoride concentration by use of a flow-cell assembly and a bifurcated fiber-optic system. A linear response was obtained for 0.16-0.95 mM fluoride at a pH of 4.1, with a response time of approximately 12 min.

Abstract: This review consists of papers mainly reported in the last decade and presents the general body of principles governing optical fiber biosensors that specifically utilise immobilized enzymes. It gives a general overview of optical fiber biosensors, their sensing principles and general instrumentation set-up used for optical fiber sensing. The possible approaches by which the immobilized enzymes are used as the recognition elements in optical fiber sensors are discussed. Surveys of the general techniques employed in the immobilization of enzymes are also presented.