American Journal of Analytical Chemistry, 2011, 2, 605-611 doi:10.4236/ajac.2011.25068 Published Online September 2011 (http://www.SciRP.org/journal/ajac) Copyright © 2011 SciRes. AJAC Determination of Mercuric Ion in Water Samples with a LED Exciting and CCD Based Portable Spectrofluorimeter Arsenio Muñoz de la Peña 1* , María Isabel Rodríguez-Cáceres 1 , Diego Bohoyo Gil 1 , María del Carmen Mahedero 1 , María del Carmen Hurtado-Sánchez 1 , Reyes Babiano 2 1 Department of Analytical Chemistry, University of Extremadura, Badajoz, Spain 2 Department of Organic and Inorganic Chemistry, University of Extremadura, Badajoz, Spain E-mail: * arsenio@unex.es Received March 29, 2011; revised June 3, 2011; accepted June 15, 2011 Abstract The fluorescent characteristics of a fluorimetric chemosensor for mercuric ion, Hg 2+ , employing a synthe- sized Rhodamine 6G derivative, have been analyzed. For that, a portable spectrofluorimeter composed of a 515 nm LED as excitation source, two fiber-optics and a CCD camera as detector, has been used, intended for “in situ” analysis. A highly selective Rhodamine based probe for Hg 2+ , that is water soluble and gives a positive response upon analyte binding, is reported. The reagent is bearing a monothiospirolactone group in a Rhodamine 6G architecture and the thiol atom served for the direct attack of thiophilic Hg 2+ . The fluores- cence enhancement is attributed to the spirolactone ring opening and the coordination of two sulphur atoms to Hg 2+ giving a 2:1 reagent: Hg 2+ stoichiometry complex. Keywords: Chemosensor, LED, Mercuric Ion, Water Analysis 1. Introduction Mercury is widely distributed in the air, water and soil, and is considered by the Environmental Protection Agency (EPA) to be a highly dangerous element because of its severe inmunotoxic, genotoxic and neurotoxic effects [1]. It is generated by volcanic emission and in several hu- man activities as gold mining, combustion of solid waste or burning of fossil fuels. The great time of residence of mercury in vapour state and his easy oxidation to inor- ganic species of Hg 2+ soluble in water have caused envi- ronmental Hg 2+ levels. Mercury easily passes through biological membranes such as skin, respiratory and gas- trointestinal tissues. When absorbed in human body, mercury causes damage to the central nervous and endo- crine systems as well as neurological irreversible dam- ages. The toxicity of mercury is known to be highly de- pendent on its chemical form: organomercury is gener- ally more toxic than inorganic mercury salts [2]. Recently, a variety of selective and sensitive fluores- cent Hg 2+ chemosensors have been developed based on fluorescein derivatives [3-6], NO 2 S 2 -donor macrocyle [7], naphthalimide [8,9], BODIPY [10-12] or Rhodamine derivatives [13-23]. BODIPY (boron dipyrromethene) fluorophores have been widely used for the determination of Hg(II). Those fluorophores have high absorption coefficient (ε > 50000 M –1 cm –1 ), high fluorescence quantum yield (Φ > 0.5), and high photostability [24]. Polyamide receptor photo- electron transfer (PET) based fluorescent sensor mole- cules could be used to detect Hg 2+ ions with either fluo- rescence off-on response or fluorescence colour change [8]. J. Wang et al. used a series of polyamide receptors incorporating two, three and four amide arms to the BODIPY fluorophore. They observed that a clear emis- sion turn-on response when as low as 2 ppb (content limit in drinking water set by EPA) of Hg(II) are present. Thus, the sensor is practical as Hg 2+ ion “annunciator” for drinking water [10]. On the other hand, J. Du et al. synthesized a highly selective PET fluorescent sensor for Hg 2+ containing a BODIPY fluorophore and a NS 2 O 2 pentachelating receptor. With this sensor the Hg 2+ could be detected in a wide pH range [11]. Also, thiacrown and crown ethers have been appended to BODIPY fluoro- phores [12]. Rhodamines are classic dyes/fluorophores whose photo- chemical properties have already been well studied. Be- cause of their low cost, long-wavelength (> 500 nm) ab- sorption/emission and high molar absorption coefficient and quantum yield, these fluorophores are usually util-