Desenvolvimento de um sensor ��ptico para determina����o de Norfloxacina

A presente disserta����o descreve o desenvolvimento e a caracteriza����o de sensores ��pticos com base em membranas de poli(cloreto de vinilo), PVC, para determina����o de Norfloxacina em amostras do sector da aquacultura. Estes sensores basearam-se na reac����o colorim��trica entre um metal imobilizado em PVC e a Norfloxacina. O metal foi escolhido com base em ensaios pr��vios de reac����o colorim��trica entre a Norfloxacina e v��rias esp��cies met��licas, nomeadamente, Fe(III), Al(III), Pb(II), Aluminon, Mo(II), Mn(II), Ni(II), Cu(II), Co(II), Sn(II) e V(V). A reac����o mais intensa foi obtida com o Fe(III). Neste sentido, numa primeira fase foram desenvolvidos sensores baseados em Fe(III). O efeito de alguns par��metros experimentais na resposta desses sensores foi avaliado de modo univariado. Incluem-se aqui o efeito do pH, avaliado entre 2,00 e 6,00, e o da concentra����o de Fe(III), variada entre cerca de 1,00x10-5 M e 2,00x10-4 M. Os melhores valores foram obtidos a pH 3, para o qual se verificou um comportamento linear entre cerca de 1,00x10-5 M e 1,70x10-4 M de Fe(III). Utilizando as condi����es seleccionadas anteriormente, procedeu-se �� caracteriza����o do complexo sob ponto de vista qu��mico. Os valores obtidos apontaram para a necessidade de um excesso de Fe(III) de, pelo menos, 10 vezes, no sentido de garantir a m��xima extens��o de complexa����o. O complexo referido apresentou, nestas condi����es, um comportamento linear ao longo do intervalo de concentra����es de cerca de 7,00x10-5 M a 7,00x10-4 M em NOR. O complexo formado foi est��vel ao longo de 90 minutos. As condi����es ��ptimas para an��lise desse complexo numa superf��cie s��lida foram obtidas ap��s avalia����o do efeito da quantidade de Fe(III) e do tipo e quantidade de solvente mediador (o-nitrofenil octil ��ter, di-n-octilftalato, dibutilftalato, bis(etilhexil)sebacato, bis(etilhexil)ftalato). O bis(etilhexil)sebacato foi o solvente mediador escolhido e a rela����o de quantidade entre o PVC e o solvente mediador foi igual a 1:2. O procedimento de prepara����o do sensor s��lido e subsequente optimiza����o foi aplicado a outras esp��cies met��licas, para al��m do Fe(III), tais como, Cu(II), Mn(II) e aluminon. A conjuga����o de todos estes metais permitiu desenvolver um array de sensores para despistagem de Norfloxacina em ��guas de aquacultura. Algumas membranas sensoras foram aplicadas com sucesso no controlo de Norfloxacina em amostras de ��guas ambientais dopadas. Os resultados obtidos com membranas de Fe(III) e Cu(II) foram exactos, tendo-se registado valores de concentra����o pr��ximos dos reais. O m��todo proposto permitiu, por isso, a despistagem r��pida e eficaz da presen��a de um antibi��tico em ��guas ambientais, permitindo ainda o seu doseamento a um baixo custo. Numa perspectiva de rotina, e tendo em vista a despistagem deste antibi��tico, este m��todo revelou-se mais r��pido e mais barato do que os demais m��todos descritos na literatura para este efeito.

MnFe2O4@CNT-N as novel electrochemical nanosensor for determination of caffeine, acetaminophen and ascorbic acid

For the first time, a glassy carbon electrode (GCE) modified with novel N-doped carbon nanotubes (CNT-N) functionalized with MnFe2O4 nanoparticles (MnFe2O4@CNT-N) has been prepared and applied for the electrochemical determination of caffeine (CF), acetaminophen (AC) and ascorbic acid (AA). The electrochemical behaviour of CF, AC and AA on the bare GCE, CNT-N/GCE and MnFe2O4@CNT-N/GCE were carefully investigated using cyclic voltammetry (CV) and square-wave voltammetry (SWV). Compared to bare GCE and CNT-N modified electrode, the MnFe2O4@CNT-N modified electrode can remarkably improve the electrocatalytic activity towards the oxidation of CF, AC and AA with an increase in the anodic peak currents of 52%, 50% and 55%, respectively. Also, the SWV anodic peaks of these molecules could be distinguished from each other at the MnFe2O4@CNT-N modified electrode with enhanced oxidation currents. The linear response ranges for the square wave voltammetric determination of CF, AC and AA were 1.0 �� 10���6 to 1.1 �� 10���3 mol dm���3, 1.0 �� 10���6 to 1.0 �� 10���3 mol dm���3 and 2.0 �� 10���6 to 1.0 �� 10���4 mol dm���3 with detection limit (S/N = 3) of 0.83 �� 10���6, 0.83 �� 10���6 and 1.8 �� 10���6 mol dm���3, respectively. The sensitivity values at the MnFe2O4@CNT-N/GCE for the individual determination of AC, AA and CF and in the presence of the other molecules showed that the quantification of AA and CF show no interferences from the other molecules; however, AA and CF interfered in the determination of AC, with the latter molecule showing the strongest interference. Nevertheless, the obtained results show that MnFe2O4@CNT-N composite material acted as an efficient electrochemical sensor towards the selected biomolecules.

Strange Dynamics in a Fractional Derivative of Complex-Order Network of Chaotic Oscillators

We study the peculiar dynamical features of a fractional derivative of complex-order network. The network is composed of two unidirectional rings of cells, coupled through a "buffer" cell. The network has a Z3 �� Z5 cyclic symmetry group. The complex derivative D����j��, with ��, �� ��� R+ is a generalization of the concept of integer order derivative, where �� = 1, �� = 0. Each cell is modeled by the Chen oscillator. Numerical simulations of the coupled cell system associated with the network expose patterns such as equilibria, periodic orbits, relaxation oscillations, quasiperiodic motion, and chaos, in one or in two rings of cells. In addition, fixing �� = 0.8, we perceive differences in the qualitative behavior of the system, as the parameter c ��� [13, 24] of the Chen oscillator and/or the real part of the fractional derivative, �� ��� {0.5, 0.6, 0.7, 0.8, 0.9, 1.0}, are varied. Some patterns produced by the coupled system are constrained by the network architecture, but other features are only understood in the light of the internal dynamics of each cell, in this case, the Chen oscillator. What is more important, architecture and/or internal dynamics?

Electrochemical sensor for simultaneous determination of herbicide MCPA and its metabolite 4-chloro-2-methylphenol. Application to photodegradation environmental monitoring

The development and application of a polyaniline/carbon nanotube (CNT) cyclodextrin matrix (PANI-��-CD/MWCNT)-based electrochemical sensor for the quantitative determination of the herbicide 4-chloro-2-methylphenoxyacetic acid (MCPA) and its main transformation product 4-chloro-2-methylphenol in natural waters are described. A simple cyclic voltammetry-based electrochemical methodology, in phosphate buffer solution at pH 6.0, was used to develop a method to determine both MCPA and 4-chloro-2-methylphenol, without any previous extraction or derivatization steps. A linear concentration range (10 to 50 ��mol L���1) and detection limits of 1.1 and 1.9 ��mol L���1, respectively, were achieved using optimized cyclic voltammetric parameters. The proposed method was successfully applied to the determination of MCPA and 4-chloro-2-methylphenol in natural water samples with satisfactory recoveries (94 to 107 %) and in good agreement with the results obtained by an established high-performance liquid chromatography technique, no significant differences being found between the methods. Interferences from ionic species and other herbicides used for broad-leaf weed control were shown to be small. The newly developed methodology was also successfully applied to MCPA photodegradation environmental studies.