Juliana Terra

Sobre o desenvolvimento da análise volumétrica e algumas aplicações atuais

Classical methods of analysis played a fundamental role in the development of Chemistry and the chemical industry. They have been tools for analytical procedures since the 18th century, remaining useful until today. The technological appeal of the instrumental methods seems to dazzle the incoming generations of chemists who do not recognize the importance of titrimetry. A short description of the development of titrimetry is presented in order to call attention to historical landmarks for teaching and learning activities in Portuguese. A compilation of some current standard analytical methods that employ titrations is presented to illustrate the availability of titrimetry nowadays.

Fast direct determination of titanium dioxide in toothpastes by X-Ray fluorescence and multivariate calibration

Recentemente, o dioxido de titânio foi classificado como potencialmente carcinogenico pela International Agency for Research on Cancer (IARC). Dioxido de titânio e um pigmento geralmente utilizado como opacificante em cremes dentais, porem sua concentracao nao e indicada nos rotulos dos produtos. Neste estudo, 22 amostras de cremes dentais foram calcinadas a 800 oC e o teor de TiO2 foi determinado por fluorescencia de raios X por energia dispersiva (EDXRF) atraves do metodo de parâmetros fundamentais (FP). As mesmas amostras foram irradiadas in natura por 100 s e, atraves da correlacao dos espectros e das concentracoes anteriormente determinadas, um modelo multivariado de calibracao foi construido. Oito variaveis latentes descreveram o modelo de regressao de minimos quadrados parciais (PLS) com erros medios de 9,5%, indicando que alem do pico referente ao titânio, as informacoes do espalhamento da radiacao tambem sao importantes para minimizar os erros ao usar uma calibracao univariada. A rapidez das analises, com minimo pre-tratamento das amostras, e a grande vantagem do metodo, que tem frequencia analitica de 24 determinacoes por hora.

Use of portable X-ray fluorescence to discriminate brands of nail polishes: a potential forensic tool

In forensic analysis, a small quantity of a particular material (hairs, fibers, soils, glasses, paints, among others) can be important to elucidate the sequence of events in a crime scene or to establish the relationship among subjects and facts. There are several examples of cosmetics used as forensic evidences, such as lipsticks and nail polishes. The composition of nail polishes varies according to brand, color and purpose of the product. In this work, the separation of Brazilian nail polishes according to their brand was evaluated using a portable energy dispersive X-ray fluorescence spectrometer (EDXRF) and principal component analysis (PCA). The nonsupervised classification of five brands indicates that the proposed methodology may be a quick, low cost and green alternative to discriminate brands and other characteristics related to a nail polish sample, as possible evidence in crime scenes.