Coumarin content of guaco syrup stored at different temperatures

Abstract

Theproduction of guaco syrup, obtained from guaco (Mikania glomerata Spreng., Asteraceae) fluid extract, and commercialized by the University Pharmacy of the Federal University of Juiz de Fora-MG, Brazil, led to a research project whose main aim was to study the stability of the finished product, with reference to the coumarin content of samples stored at different temperatures. UV spectrophotometry (275.4 nm) was used to assess the coumarin content of the study syrup. An 80% v/v methanol/distilled water mixture was used for sample dilution. The calibration curve was constructed by the dilution of 100 mg standard coumarin in 100 ml of the aforementioned solution, with seven distinct concentrations (ranging from 2 μg a 20 μg) being obtained. The results showed the 45°C storage temperature to be optimum for the development of trans-cis isomerization, with subsequent conversion of the latter into coumarin. Coumarin content in the studied pharmaceutical presentation ranged from 1.19 to 1.37 mg/mL, the highest value corresponding to the samples stored at 45°C for six months.