Standard rutin (PVP, Parnaíba, Brazil), NF XI secondary
standard without any further purification (96.1%, NF XI,
lot 02134, expiration date 07/2005), was dissolved in
95.0% ethanol and 0.02M acetic acid (99 + 1; LabSynth, São
Paulo, Brazil) to concentrations from 5.0 to 15.0 g/mL. The
absorbance measurements were obtained at 361.0 nm using
Spectrophotometer Beckman DU–640 with a 1 cm quartz
cuvette. Means of 6 replicates of each concentration value
were used to construct the calibration curve. The linearity was
analyzed and confirmed by statistical analysis (4, 32).