Development and validation of a micellar electrokinetic chromatography method for quantitative determination of butenolides in Piper malacophyllum (C. Presl) C. DC. - Oliveira, Alberto de; Silva, Claudinei Alves da; Silva, Adalberto Manoel da; Tavares, Marina Franco Maggi; Kato, Massuo Jorge (Phytochemical Analysis, 2010)