Ligand sensitized fluorescence of uranyl in its fluoride complex by picolinic acid : An application for trace fluoride ion determination

Analytical Chemistry and Spectroscopy Section, Chemistry Group, Indira Gandhi Centre for Atomic Research, Kalpakkam-603 102, Tamilnadu, India E-mail : siuli@igcar.gov.in Picolinic acid has been used to form complex with uranyl fluoride to enhance the fluorescence intensity by about two times. Linearity in fluorescence intensity of uranyl-fluoride-picolinatt complex was obtained in the range of fluoride concentration of 40-400 ppb. The quenching effect of ions like CI-, NO3 -, SO42-, CO32- and Fe2+ on the fluorescence intensity of uranyl-fluoride and uranyl-fluoride-picolinate complexes have been studied. Stern-Volmer quenching constants for these quenchers were found to be about five times less in uranyl-fluoride-picolinate complex as compared to uranyl-fluoride complex. Fe2+ ion is found to have severe quenching effects on the fluorescence intensity of both the complexes of uranyl. This method can be used for determination of trace amount of fluoride in water samples with the tolerance limits of NO3- (20 ppm), SO42- (60 ppm), CO32- (100 ppm) and CI- (2 ppm)