Fluorescent sensing and determination of mercury (II) ions in water

The presence of heavy metals released from industrial activities into water streams is an ever-growing challenge to ensuring a safe and clean aquatic environment. Detection and determination of the levels of these heavy metals in wastewater is an important step before any measures can be taken. In this study we report on a fluorescent sensing probe based on a naphthyl azo dye modified dibenzo-18-crown-6-ether (DB18C6) for the detection and determination of mercury (II) ions in water. The probe showed high sensitivity and selectivity towards the mercury (II) ion among various alkali, alkaline earth, and transition metal ions. The mercury (II) ion quenched the fluorescence of the probe. Stern-Volmer quenching constants (K_sv) were found to be highest for Hg²⁺ ion at 1.18 × 10⁵ M^-1 compared to 3.85 × 10⁴ M^-1 for copper (II) ion. The stoichiometry of the sensor-metal ion interaction was found to be 1:1 for both metal ions using Job plots. The detection limit for Hg²⁺ was 1.25 × 10^-8 M. The dye modified crown ether was then used to detect mercury in a water sample from a coal-fired power plant and to determine the amount of mercury in the water sample.