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Environmental Engineering Research 2012;17(S1): S75-S78. DOI: https://doi.org/10.4491/eer.2012.17.S1.S75
Methyl Red: A Fluorescent Sensor for Hg2+ over Na+, K+, Ca2+, Mg2+, Zn2+, and Cd2+
Diganta Kumar Das , Priyanka Goswami , Champa Barman , and Biva Das
Department of Chemistry, Gauhati University, Guwahati 781014, Assam, India
Corresponding Author: Diganta Kumar Das  ,Tel: +91-361-2570535, Fax: +91-361-2570535, Email: digantakdas@gmail.com
Received: September 17, 2012;  Accepted: October 10, 2012.
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Methyl red (MR), a very well known acid base indicator (pKa = 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 Hg2+ 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 Hg2+ ion becomes 1:1. Similar titration with a number of other metal ions, namely Na+, K+, Ca2+, Mg2+, Zn2+, and Cd2+, has very small effect on the fluorescent intensity of MR. Thus MR acts as a selective fluorescent sensor for Hg2+ 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 Hg2+ 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.
Keywords: Fluorescence | Hg2+ ion | Methyl Red | Quenching | Sensor
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