Fig. 2
Standard curves generated with purified poplar condensed tannin. Each point in the main panel represents the mean of at least two independent values (±SE). Best fit lines were drawn through all data when using acetone-free method (74% butanol/3.9% 12 N concentrated HCl/15.6% MeOH/3.9% H2O/2.6% Fe-reagent) and between absorbance values of 0.07–1.54 for acetone-based method (50.1% acetone/33.5% butanol/3.9% 12 N concentrated HCl/2.9% MeOH/7% H2O/2.6% Fe-reagent). The preferred absorbance range for CT quantification when using acetone-based method was from 0.158 to 1.247 (abs. value ± 3 × SE). In the inset, samples with the four most concentrated CT standards (open circles) were diluted by 50% (crosses) and absorbance readings repeated. The comparison to equivalent concentrations of undiluted extract (solid circles) indicates that a discrepancy in predicted and actual absorbance values, suggesting that post-assays dilution will lead to erroneous results