Two habitual methods for assessing tannin levels, the
Folin–Ciocalteau method and the ferrous tartrate method, which
were based on spectrometry, were utilized as references for
verifying the proposed system. Because of the different linear
ranges of spectrometry of the two reference methods, the low
(20–50gmL−1) and high (100–300gmL−1) concentration
ranges of tannic acid in the proposed method were verified using
the Folin–Ciocalteau method and the ferrous tartrate method,
respectively. Fig. 6 shows that good correlations were obtained
with both the Folin–Ciocalteau method (r2 = 0.9808) and the
ferrous tartrate method (r2 = 0.9899), respectively