Gas-diffusion flow injection assay for the selective determination of chlorine dioxide based on the fluorescence quenching of chromotropic acid

The present work reports the first spectrofluorimetric gas-diffusion flow injection (GD-FI) assay for the determination of chlorine dioxide in water samples (tap, mineral and soda water). The method is based on the fluorescence quenching of chromotropic acid (CA) (lambda(ex)= 347 nm, lambda(cm) = 371 nm) caused by the analyte. The chemical and instrumental variables of the system were studied in terms of maximum sensitivity. The gas diffusion cell was thermostated at 40 degrees C to enhance the vaporization of chlorine dioxide and thus the sensitivity of the method. The quenching effect of chlorine dioxide on CA was linear in the range 0.09-3.41 mg l(-1), while the precisions either close to the quantitation limit or near to the middle of the linear section of the calibration graph were satisfactory in both cases (Sr= 2.6% and 1.5% (n = 10) at 0.17 and 1.71 mg l(-1) level, respectively). The developed method proved to be adequately selective and sensitive with 3 sigma limit of detection equal to c(L)= 0.03 mg l(-1). The application of the assay to spiked tap, mineral and soda water samples yielded accurate results with recovery values in the range 94.1 -105.9%. (c) 2005 Elsevier B.V. All rights reserved.