Made available in DSpace on 2015-05-14T13:21:45Z (GMT). No. of bitstreams: 1 parte1.pdf: 2505729 bytes, checksum: e872a92484e063cf1f264ba7b16d9e2e (MD5) Previous issue date: 2010-03-19 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / This work proposes the use of digital images captured by a Webcam for determination of total acidity in red wines by means of an acid-base titration without using an external indicator. Digital images present the colour of the emergent radiation, which is complementary to the radiation absorbed by molecules of anthocyanines presents in wines. Each image, generated according to RGB system, yields a matrix of the values of the R, G and B components whose averages define a the colour value obtained as: 2R ⋅2G ⋅2B. This value was adopted as analytical response to build titrations curves based on digital images (DIB). For a more precise localization of the end point, titrations curves were generated on the basis of the second derivative values of the analytical response. Anthocyanines present different colours according to medium pH and, from the variation of the colour values of the images obtained during the titration of the red wines, the end point could be detected with precision. The official method recommends the use of potenciometric titration for determination of total acidity in red wines. This method requires a dilution of the sample before the titration that must be carried out until a fixed value of pH (8.2 8.4). In order to illustrate the feasibility of the proposed method titrations involving the determination of total acidity in ten red wines samples were carried out. Results were compared to the ones obtained by potenciometric titration used as reference method. No statistic difference has been observed between the results by applying the paired t-test at 95% confidence level. The proposed method yielded results with a better precision than the official method. These advantageous characteristics are attributed to the trivariate nature of the measures associated to digital images. / Neste trabalho, propõe-se o uso de imagens digitais, capturadas com uma Webcam, para determinação da acidez total de vinhos tintos por meio de titulação ácido-base sem a utilização de indicador externo. As imagens digitais apresentam a cor da radiação emergente que é complementar à da radiação absorvida por moléculas de antocianinas presentes nos vinhos. Cada imagem, gerada de acordo com o sistema vermelho-verde-azul (RGB), fornece uma matriz de valores dos componentes R, G e B cujas médias definem o valor de cor obtido como: 2R ⋅2G ⋅2B. Esse valor foi adotado como resposta analítica para a construção das curvas de titulação baseadas em imagens digitais (DIB). Para a localização mais precisa do ponto final, foram geradas as curvas de titulação com base nos valores da segunda derivada da resposta analítica. As antocianinas apresentam diferentes cores de acordo com o pH do meio e, a partir das variações do valor de cor das imagens obtidas durante a titulação dos vinhos tintos, o ponto final pôde ser detectado com precisão. O método oficial recomenda o uso da titulação potenciométrica para a determinação da acidez total de vinhos tintos. Este método requer diluição da amostra antes da titulação que deve ser efetuada até um valor fixo de pH (8,2-8,4). A fim de ilustrar a viabilidade do método proposto, foram realizadas titulações envolvendo a determinação da acidez total em dez amostras de vinhos tintos. Os resultados foram comparados com os obtidos pela titulação potenciométrica usada como método de referência. Constatou-se que não há diferença sistemática estatisticamente significativa entre os resultados, aplicando-se o teste t emparelhado ao nível de 95% de confiança. O método proposto produziu resultados com uma precisão melhor que a do método oficial. Essas características vantajosas da titulação DIB são atribuídas à natureza trivariada das medidas associadas às imagens digitais.

This diploma thesis deals with acid-base and electrolytic behavior of hyaluronan solutions at different ionic strength. Acid-base behavior of hyaluronan was investigated by acid-base titrations which were carried out with two different methods, acid and alkaline acid-base titration. Dissociation constants at different ionic strength at zero degree of dissociation and at 50% degree of dissociation were evaluated from the results of acid-base titrations. Dissociation constants obtained from acid acid-base titrations have values between 3,0 and 3,6. Dissociation constants obtained from alkaline acid-base titrations are not very informative because their values are much higher than the expected values. The study of degradation of hyaluronan during acid-base titration was performed to complete study of acid-base behavior. Electrolytic behavior of hyaluronan solution was performed by conductometric titrations in three different environments.