ORIGINAL ARTICLE Selective Fluorometric Analysis of Hg(II) in Industrial Waste Water Samples Saurabh Kumar Gupta 1 & Kavita Tapadia 1 & Ashima Sharma 1 Received: 4 August 2020 /Accepted: 24 September 2020 # Springer Science+Business Media, LLC, part of Springer Nature 2020 Abstract The highly selective and sensitive fluorometric method has been developed for trace level determination of Hg(II) is based on photo-induced electron transfer between rhodamine-6G dye and metal complex. Quenching in fluorescence intensity by fluo- rescence resonance energy transfer (FRET) is due to interaction between metal ion complex and dye. The fluorescence emitted was measured at 510 and 550 nm, for excitation and emission wavelengths respectively. Possible interferences present in water samples, which could affect the analytical response are studied and determined. The calibration graph was dynamically linear from 0.002 to 0.05 mgL -1 of Hg(II) with limit of detection 7 × 10 -4 mgL -1 and limit of quantitation 1.9 × 10 -3 mgL -1 . The Stern- Volmer constant (K SV ) calculated for the quenching of R-6G with Hg (II) was 8.47 Lmg -1 s -1 at optimized reaction conditions. The proposed FRET based fluorometric method was applied successfully in different industrial wastewater samples with satisfactory outcome. Keywords Hg(II) . Rhodamine-6G . Fluorescence . FRET . Quenching . Industrial wastewater samples Introduction Heavy metal ions are vastly spread in the environment, which play a remarkable role in many biological actions. Among the highly toxic heavy metals, mercury is one of the most studied environmental toxicant having greater impact on ecosystem as well as human wellness. Mercury is believed as the most nox- ious heavy metal, which is diffused via coal plants, mercury lamps, gold production and many anthropogenic activities. Its exposure leads to major toxicity and long term defect to flora and fauna even in minute level concentration. Toxicity de- pends upon chemical states of mercury i.e. inorganic mercury is having greater affinity towards sulfhydril moieties of pro- tein. Inorganic mercury causes harmful adverse effects when its concentration reach upto 5000 mgL -1 [1–4]. Hg 2+ (mercuric ion) are the most poisonous form of mer- cury, because of its higher water solubility and stronger affin- ity towards sulfhydryl groups or thiol (-SH) containing amino acids. Its exposure can affect the central nervous system, renal, gastrointestinal, cardiovascular, endocrine and immune sys- tem of human being resulting in memory loss, vision prob- lems, paralysis, kidney malfunction, neurological disorder, chromosomal and birth defects etc. In marine environment inorganic mercury get turned into methylmercury which is quite more toxic than the inorganic mercury. Mercury contam- ination of the environment and its toxic effects has been known for centuries. This allowed the development of conve- nient and selective analytical strategy for the efficient deter- mination of Hg 2+ [5–8]. Particularly for environmental analysis and monitoring of Hg (II), numerous analytical strategies have been developed in different matrices, such as UV-visible spectrometry [9], in- ductively coupled plasma [10, 11], cold-vapour atomic ab- sorption spectroscopy [12–14], electrochemical stripping analysis [15, 16], neutron activation analysis [17] and HPLC hyphenated with inductively coupled mass spectrometer [18, 19]. The real sample analysis of Hg 2+ is mainly performed by instrumental techniques such as AAS, ICP, HPLC, EDXRF, electrochemical methods like voltammetry etc. However, these traditional approaches suffer from many disadvantages such as highly sophisticated instrumentation, rigorous exper- imental operation as well as complicated sample pre-treat- ment. On the other hand, the advancement of optical * Kavita Tapadia ktapadia.chy@nitrr.ac.in 1 Department of Chemistry, National Institute of Technology, Raipur, CG, India Journal of Fluorescence https://doi.org/10.1007/s10895-020-02627-7