Atomic Absorption Spectroscopy

Indium tin oxide (ITO) films havebeenprepared by the sol-gel method using both organic and inorganic precursors. Acomputer-controlled dip-coating unit isdesigned and fabricated inour laboratory fora precise control of the parameters during the dip-coaling: process. Thesefilms have been characterized byX·raydiffraction. optical and electrical study and also byatomic absorption spectroscopy. Theoptimized coatings exhibita sheet resistance of around 100 010 and anaverage visible solartransmission of around 85%.

Prussian blue (PB) particles with the size of ca. 5 nm were synthesized and immobilized in a multilayer structure, as a strategy for the potential development of an amperometric transducer for oxidase-enzyme-based biosensors. Multilayer films composed of PB and poly(allylamine hydrochloride) (PAH) were prepared via layer-by-layer (LbL) sequential deposition. The process was carefully monitored by UV-vis spectroscopy and cyclic voltammetry. The increase of the redox current peaks during the layer-by-layer deposition demonstrated that charge propagation within the film occurs. Linear increase of UV-vis absorbance with the number of deposited bilayers indicates that well-organized systems have been elaborated. ITO electrodes coated with PB/PAH films were used successfully for detecting H 2 O 2 , sensitivity being dependent on the number of PB/PAH layers.

A procedure for the simultaneous determination of lead and cadmium in TiO 2 by differential pulse anodic stripping voltammetry (ASV) has been developed. The key feature of the method is the use of triethanolamine (TEA) to remove titanium interference: TiO 2 undergoes acidic digestion with HF/H 2 SO 4 at atmospheric pressure, TEA is added to the HCl solution of the residue and the solution is analysed using a standard ASV instrumentation, equipped with a hanging mercury drop electrode. The calibration curves for both lead and cadmium are linear up to 50 mg l (1 of solution, and the detection limits are 1 mg l (1 , corresponding to 1 mg g (1 of TiO 2 . Method reliability was tested by comparing the results with those given by electrothermal atomic absorption spectroscopy. The method has been successfully applied for determination of both contaminants in powdered titanium dioxide (raw materials) and in titanium dioxide-containing cosmetics (sunscreen products). # (G. D'Alfonso).

Bohr model has an atom consisting of a nucleus containing protons and neutrons surrounded by a cloud of electrons in fact inhabit specific regions in space. This is known as an orbital. The further an orbital gets from the nucleus, the more they gain potential energy associated to a determined orbital. Quantum Mechanics explains that orbitals have quantized energy levels and for moving an electron to another level, it has to receive or emit the exact amount of energy corresponding to the difference between the two electronic levels (ΔE = E 1 -E 0 ). The amount of energy required to move and electron from energy level E 0 to energy level E 1 can be provided by heat due to a collision with other particles or absorb the energy of a photon. In this case, the energy of a Photon (E = hν = hc/λ) should be equal to the difference between the orbitals (ΔE), this is, only a Photon of a particular wavelength is absorbed and can promote that transition. This phenomenon is known as atomic absorption. A more stable electron configuration of an atom is the one with less energy, also known as ground state configuration. The difference of energy between the last full orbital and the next empty orbital of the atom in a ground state is of the same order of magnitude of photons with wavelengths between 200 and 800 nm, this means, photons in ultraviolet regions and visible light of electromagnetic spectrum. Sodium atom in ground state, e.g., has an electronic configuration of 1s 2 2s 2 2p 6 3s 1 . The 3s electron can receive a photon with energy of 589.0 nm (E=2.2 eV) and passes to 3p orbital, which is an unstable state known as excited state. Being unstable, the excited atom loses its energy quickly (approximately in 10 -8 s) and returns to ground state. One way to lose excitation energy is by emitting a photon of 589.0 nm, a phenomenon known as atomic emission. A photon of 330.3 nm can also be absorbed by sodium. This is the difference of energy between 3s and a 4p orbital (3.6eV), but one photon of 400 nm cannot be absorbed because there are not two orbitals in a sodium atom with the same difference of energy. The return of electron from 4p orbital to ground state can also occur in two steps: first to 4s and then to 3s by emitting two photons with energies correspondent to the two transitions in a phenomenon known as atomic fluorescence. The sodium atom can also receive enough energy to remove an electron, turning into sodium ion (Na + ), known as ionization. In this case, a change occurs in orbitals of different energy levels, so that the ion has a new set of transition being able to absorb or emit photons of wavelengths differently from metallic sodium. Each chemical element has a unique electronic structure that differentiates from others. This implies in a possible and unique set of transitions, a set of characteristic absorption/emission lines that can be used for identification. Although the set of transitions is unique for each element, there may be a coincidence of spectrum in some lines of two or more elements, which means that different atoms can absorb or emit photons of same wavelength. Even though the theoretical basis was established in the beginning of the twentieth century, only in the early 1950s an Australian physicist, Sir Alan Walsh, proposed the phenomenon