A new fluorimetric method with rhodamine-based fluorescent agent was developed for the rapid speciation of Cr(III)/Cr(VI) in tea, soil and water samples. The system, which utilizes a fluorescent reagent, was used for the first time after synthesis/characterization of 3',6'-bis(diethylamino)-2-{[(1E)-(2,4-dimethoxyphenyl)methylene] amino}spiro[isoindole-1,9'-xanthen]-3(2H)-one (BDAS). The reagent responds instantaneously at room temperature in a 1:1 stoichiometric manner to the amount of Cr(III). The selectivity of this system for Cr(III) over other metal ions is remarkably high, and its sensitivity is below 0.01mgL-1 in aqueous solutions which enables a simplification without any pretreatment of the real sample. The method has a wide linear range of 0.1-10mgL-1 and a detection limit of 0.15μgL-1 for Cr(III) while the relative standard deviation was 0.1% for 0.1mgL-1 Cr(III) concentration. The results of detection and recovery experiments for Cr(III) in tea, soil and water were satisfactory, indicating that the method has better feasibility and application potential in the routine determination and speciation of Cr(III)/Cr(VI). The results of analysis of the certified reference material (INCT-TL-1 tea sample and CWW-TM-D waste water) are in good agreement with the certified value.
Keywords: Chromium speciation; Direct determination; Fluorescence reagent; Tea samples.
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