INDIRECT SPECTROFLUOROMETRIC DETERMINATION OF ARSENIC AT NANOTRACE LEVELS IN ALLOYS, UNDERGROUND WATER, INDUSTRIAL WATERS AND SEWAGE-SLUDGE

An inexpensive and virtually specific nonextractive spectrofluorimetri c method for the determination of As(III) (1 ng/ml-1 mu g/ml) in 0.18- 1.08 N H2SO4 has been developed. A known excess of Cr(VI) is allowed t o quantitatively oxidize As(III) in the essential presence of a mixtur e of iodide and chloride as catalyst, followed by the addition of exce ss 2-(alpha-pyridyl)thioquinaldinamide and measurement of the fluoresc ence intensity (lambda(em(max)) = 488 nm lambda(ex(max)) = 360 nm) cau sed by Cr(VI) remaining after As(III) oxidation. The measurement is re peated without As(III) addition and the decrease in fluorescence inten sity gives the As(III) concentration with the help of a calibration gr aph. The method is very precise and accurate (S. D. = +/- 0.474, R. S. D. = 0.95%, for the analysis of 50 ng/ml As(III), 11 replicates). The detection limit is 0.3 ng/ml As(III). Large excesses of over fifty ca tions, anions and some complexing agents do not interfere. The method has been successfully applied for arsenic determination in various com plex matrices: environmental waters, sewage sludges and several certif ied reference materials (alloys). This method has also been extended t o determine As(V), after its reduction to As(III), in water samples, w aste discharge water and sewage sludges.