engleski

Electrochemical, zeta-potential and particle size characterization of groundwater samples

Water is the most important chemical compound on earth essential for all living organisms. Natural and industrial waters contain different ions and particles ranging in sizes from nanometers to micrometers. The ionic and particle composition as well as their amount determines their potential application and treatment methods. Drinking water is clear, has no smell or colour and for the good taste should contain diluted oxygen, carbon dioxide and soluble salts (NaCl, NaHCO3) [1]. Groundwater contains arsenic in a form of arsenite and arsenate, which if consumed have toxic effects on humans, animals and the entire ecosystem. Millions of people from different countries (Chile, Mexico, China, Argentina, USA, Hungary, Indian State of West Bengal, Bangladesh, and Vietnam) heavily depend on groundwater which contains elevated level of arsenic for drinking purposes. Long term consumption of such water (such as 5-10 years) may cause arsenicosis, which is arsenic related health problem [2]. The main goal of our study was to detect more toxic trivalent arsenite (AsIII) in groundwater samples from Osijek region and to determine zeta potential values and particle size of the same samples. Electrochemical measurements were conducted in a three electrode voltammetric cell in a phosphate buffer at pH = 7, where modified glassy carbon electrode was used as a working electrode, Ag/AgCl a s a reference electrode and a platinum wire as a counter electrode [3]. The system was purged with high purity argon, Ar5 (Ar = 99.999 %) before each measurement. Dynamic and electrophoretic light scattering measurements were performed in order to determine zeta potential and size distribution of particles present in the sample. Arsenite was first detected in the model systems with differential pulse voltammetry where linear response was obtained in a concentration range from 2.0 mol dm-3 to 22.0 mol dm-3. Than the groundwater samples were studied and the obtained arsenite concentration varied between 2.5 mol dm-3 to 3.5 mol dm-3. Zeta potential measurements showed that particles in all groundwater samples have negative zeta potential (it varied from -2 mV to -13 mV) even though small amounts (x  3 %) of particles with positive zeta potential values were also detected in two samples. Particle size measurements revealed monomodal, bimodal and trimodal particle size distributions while the most common particle size in all samples was in a nm range (it varied from 393 nm to 808 nm).

voltammetry, modified electrode, arsenite detection, zeta potential, groundwater

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