Synthesis And Analytical Application Of Novel Fluorescent Hg²⁺ Probes Derived From Rhodamine Fluorophore

Mercury is a highly toxic metallic element in nature. It can lead to serious environmentalpollution. Once absorbed by the body, it will cause a disease of the central nervous system,kidneys and endocrine system. The other hand, due to human factors or natural factors,inorganic mercury is released into the natural environment, and then converted to organicmercury by aquatic microbial methylation. Organic mercury is more dangerous than inorganicmercury， because it can easily pass through the biofilm. Methylmercury is a typical organicmercury. And it can cause human cardiovascular disease, deafness, loss of civilization andeven death. Therefore, timely, sensitive and highly selective detection of Hg²⁺has importantsignificance for environment protection and human health.Fluorescence detection is widely used in Hg²⁺determination because of its simpleoperation, simple data collection, and good reproducibility. Rhodamine B and its derivativesare a class of well-known fluorescent dyes. Due to the high fluorescence quantum yield, highextinction coefficient and longer excitation and emission wavelength of rhodamine, it iswidely used in the determination of metal ions and the biologically active substance. But poorlight stability and the weak selectivity is its disadvantage. This paper introduced a sulfur atom,having a stronger affinity for Hg²⁺, to prepare the rhodamine B thiohydrazide. And then wedesigned and synthesised three rhodamine thiohydrazide derivatives fluorescent probes basedon the theory of hard and soft acids and the results of the previous work. Their structure hasbeen characterized, and their fluorescence spectrometry for detecting Hg²⁺has been examed.We found that they have a wider linear range, good selectivity, high sensitivity andreversibility.The main job contents are as follows:（1） A novel fluorescence probe was designed, synthesized which is3’,6’-bis（diethylamino）-2-（（4-fluorobenzylidene）amino）spiro[isoindoline-1,9’-xanthene]-3-thione （RBS1）. Its structure was characterized with IR, elemental analysis and1H NMR. Thefluorescence intensity of probe itself is very weak, but after the combination with Hg²⁺, itincreased obviously. Thus, a new method for the determination of Hg²⁺was established. Theoptimum detection conditions were as follows: pH of4.5，reaction time of25min. It exhibitsa dynamic response concentration range for Hg²⁺from to5.00×10^-9mol/L-1.00×10^-6mol/Lwith a detection limit of1.93×10^-9mol/L and the linear correlation coefficient was0.9997.The standard recovery for river sample and soil sample were102.22%and94.24%respectively. The results show that the probe has a higher selectivity and sensitivity. （2） A novel probe，3’,6’-bis（diethylamino）-2-（（2,4-dimethoxybenzylidene）amino）spiro[isoindoline-1,9’-xanthene]-3-thione （RBS2）， was designed and synthesized. Itsstructure was characterized with elemental analysis, IR spectra and1H NMR. Thefluorescence intensity of probe itself is very weak, but after the combination with Hg²⁺, itincreased obviously. Thus, a new method for the determination of Hg²⁺was established. Themeasurement conditions have been optimized: pH of4.0，reaction time of25min. Itsdynamic response concentration range and detection limit for Hg²⁺were5.00×10^-9mol/L to1.00×10^-6mol/L detected and1.83×10^-9mol/L, respectively. The standard recovery for riversample and soil sample were104.47%and102.53%respectively.（3） A novel fluorescence probe，3’,6’-bis（diethylamino）-2-（（2-hydroxy-4-methoxybenzylidene）amino）spiro[isoindoline-1,9’-xanthene]-3-thione （RBS3）, was designed andsynthesized. Its structure was characterized with IR, elemental analysis and1H NMR. Thefluorescence intensity of probe solution is very weak, but after the combination with Hg²⁺, itincreased obviously. A new method for the determination of Hg²⁺was established. Themeasurement conditions have been optimized. It exhibits a dynamic response concentrationrange for Hg²⁺from5.00×10^-9mol/L to1.10×10^-6mol/L with a detection limit of2.82×10^-9mol/L. The standard recovery for river sample and soil sample were99.75%and98.07%respectively.