A DERIVATIVE UV SPECTROPHOTOMETRIC METHOD FOR THE DETERMINATION OF METHYLXANTHINES AND TANNINS IN GUARANA BULK (PAULLINIA CUPANA)

A method using derivative UV spectrophotometry was developed and validated for the determination of methylxanthines and tannins in guarana bulk, using caffeine and catechin as markers. The spectra were obtained using first order derivatization, Δλ=20.000, and scale factor of 10. The quantification of actives was performed using wavelengths of 244 and 277 nm for catechin and caffeine, respectively. The parameters of specificity, linearity, precision, accuracy, robustness, limits of detection (LOD) and quantification (LOQ) were established to validate the method. The method was shown to be specific for quantification of methylxanthines and tannins, and linear over the concentration range 5–35 µg mL^-1, with a correlation coefficient of r=1(caffeine) and r=0.9993 (catechin). The results indicated good intra-day and inter-day precision with RSDs less than 2%. The method was accurate, exhibiting recoveries between 98 and 102%. The LODs were 0.184 µg mL^-1 (caffeine) and 0.368 µg mL^-1 (catechin), and the LOQs were 0.552 µg mL^-1 (caffeine) and 1.104 µg mL^-1 (catechin). Methylxanthines and tannins were quantified, and contents of 10 µg mL^-1 and 20 µg mL^-1, respectively, were observed