Development and validation of micellar electrokinetic chromatography (MEKC) method for the quantitative determination of butenolides in Piper malacophyllum - Oliveira, Alberto de; Silva, Claudinei Alves da; Silva, Adalberto Manoel da; Tavares, Marina Franco Maggi; Kato, Massuo Jorge (Brazilian Conference on Natural Products - BCNP, 2007)