Methyl Red: A Fluorescent Sensor for Hg2+ over Na+, K+, Ca2+, Mg2+, Zn2+, and Cd2+

Diganta Kumar Das, Priyanka Goswami, Champa Barman, Biva Das
2012 Environmental Engineering Research  
Methyl red (MR), a very well known acid base indicator (pK a = 5.2), shows fluorescence emission in the range 320 nm to 480 nm, with an emission maximum at 375 nm on excitation by photons at 310 nm. A fluorescent intensity titration of MR by Hg 2+ ion, a well known toxic heavy metal ion, shows quenching of the fluorescent intensity of MR. The quenching continues till the concentration ratio between MR and Hg 2+ ion becomes 1:1. Similar titration with a number of other metal ions, namely Na + ,
more » ... + , Ca 2+ , Mg 2+ , Zn 2+ , and Cd 2+ , has very small effect on the fluorescent intensity of MR. Thus MR acts as a selective fluorescent sensor for Hg 2+ ion by selective fluorescence quenching. The efficiency of fluorescence quenching value is found to be 8.0. The binding ratio and binding constant (β) between MR and Hg 2+ ion are calculated from the fluorescence and UV/visible spectral data, and are found to be 1:1 and log β =4.68. The Hg:MR complex was found to be stable in the pH range 5.5 to 8.2.
doi:10.4491/eer.2012.17.s1.s75 fatcat:oamwn54ymzbpjkrh5hfftbeusy