A method was developed for the analysis of ester-linked phenolic acids in forage samples using extraction by an ultrasound-assisted treatment and quantification by HPLC with a UV-VIS detector. A reversed-phase C18 column was used for developing the method and the optimal condition was established with isocratic elution using acetonitrile/methanol/H 3 PO 4 pH 2.08 (13:12.5:74.5) as the mobile phase. To reduce the time of sample processing, the extraction of ester-linked phenolic acids was studied using ultrasound bath and the results were then compared with those from an extraction usual using alkaline hydrolysis (20˚C for 24 h). The method was valued through external and internal calibration. Internal calibration using o-coumaric acid as internal standard and m-coumaric acid as surrogate internal standard showed better results. The detection limits were of 0.09 and 0.04 mg·L -1 for p-coumaric and ferulic acids, respectively. The proposed method showed a good linear dynamic range (3.00 -30.00 mg·L -1 ) for the analytes. The usefulness of the method-ology was demonstrated by addition-recovery experiments using forage samples and values were in the 83 to 99% range. The extraction of ester-linked phenolic acids by 120 minutes of ultrasound bath was faster and more reproducible than alkaline hydrolysis (20˚C for 24 h).

À professora Dra. Marina Franco Maggi Tavares, obrigada pelos ensinamentos, paciência e orientação e diversas oportunidades de amadurecimento profissional. Ao professor Dr. João Pedro Simon Farah pela contribuição na parte estatística deste projeto. Agradeço também pelas aulas teóricas e inúmeros conselhos. Ao professor Dr. Claudimir Lúcio do Lago pelas contribuições neste trabalho durante o afastamento por licença sabática da professora Dra. Marina Tavares. Ao professor Dr. Marcelo Tavares pela parceria neste projeto, pelo esclarecimento nos assuntos biológicos e pela concessão das amostras. Aos professores da UFJF Dra. Maria Auxiliadora Costa Matos e Dr. Renato Camargo Matos, pelos incentivos em realizar o mestrado em São Paulo. Aos professores doutores Jivaldo do Rosário Matos e Lúcio Agnes pelos ensinamentos em Química Analítica.