Neste trabalho são descritos e comparados dois métodos espectrofotométricos para análise de catecol (o-hidroxifenol) em Paullinea cupana var. sorbilis, popularmente conhecido como guaraná. As amostras de sementes trituradas foram extraídas com etanol 97% v/v e as soluções tratadas com p-aminofenol em meio etanólico alcalino ou m-aminofenol e metaperiodato de sódio em solução tampão (pH 3.0). A absorbância foi medida a 586 nm e 520 nm respectivamente. Quatro produtos comerciais diferentes foram analisados e os resultados foram comparados com aqueles obtidos com m-aminofenol. Apesar da boa qualidade das curvas de calibração, nos dois métodos houve interferência da matriz, o que foi contornado usando-se o método da adição de padrão. A comparação entre os resultados obtidos pelos dois métodos, usando o teste estatístico t de Student, mostrou que não há diferenças significantes para um nível de confiança de 95%.In this article are described and compared two spectrophotometric methods for the analysis of catechol (o-hydroxyphenol) in Paullinea cupana var. sorbilis, popularly known as guaraná. The pounded seed samples were extracted with ethanol 97% v/v and the solutions were treated with p-aminophenol in alkaline ethanolic medium or m-aminophenol and sodium metaperiodate in buffered aqueous solution (pH 3.0). The absorbance was measured at 586 nm and 520 nm respectively. Four different commercial products were analyzed and the results were compared with those obtained with the m-aminophenol method. Despite the good quality of the calibration curves, in the two methods the interference of the matrix was observed. This problem was settled using the standard addition method. Comparison between the results obtained by the two methods, using the statistical Student's t-test, showed that there is no significant difference at the 95% confidence level.

A flow injection piezoelectric procedure is proposed for the determination of brix (total solids dissolved) in the alcoholic fermentation process. A piezoelectric Perspex cell was constructed to fit one of the gold electrodes of a 10 MHz crystal and this sensor was adapted to a flow injection system. The analytxal curve is linear over the brix range from 0.5 to 20.0% with a detection limit of 0.3 %.Seventy results can be obtained per hour and the relative standard deviation was less 2411 2412 MAGNA, DE OLIVEIRA, AND FATIBELLO-FILHO than 1.45% for a solution containing 6% of brix (n=15). Applications of this method for the determination of brix in sugar cane juice and in an alcoholic fermentation bench show satisfactory results in comparison with refractometric and densimetric methods, respectively.