Development of an optical fibre reflectance sensor for lead detection based on immobilised arsenazo III

A fibre-optic sensor based on the use of 2,7-bis(2-arsenophenylazo) 1,8-dihydroxynaphthalene-3,6-disulphonic acid, commonly called Arsenazo III (ASA III) immobilized onto XAD-16, has been developed for the rapid reflectance spectrometric determination of lead (II). The measurements were carried out at a wavelength of 664.6 nm since it yielded the largest divergence different in reflectance spectra before and after reaction with the analyte element. The sensor was found to have an optimum response at pH 5.0 with respective measurement repeatability and probe-to-probe reproducibility of 0.23% and 2.3%. The dynamic working response of Pb(II) was found within the concentration range of 0.2–20.7 ppm, with a LOD of 0.01 ppm. The tolerance limits of coexisting ions were also investigated. The sensor can easily be regenerated by immersion in 0.1 mol/L HNO3. The proposed sensor was applied to the determination of Pb(II) in commercial gasoline after wet ashing of sample with satisfactory results.