Quantitative spot test analysis of soluble tannin in green tea using a portable diffuse reflectometer

The study proposes a low cost and very simple quantitative spot test technique for determination of soluble tannin in green tea samples using a portable diffuse reflectometer. The lab-made instrument was made of polytetrafluoroethylene (PTFE), using a light emitting diode (LED) for its light source, and a phototransistor as the detector. The proposed method measured diffuse reflectance from a complex formed by reaction between soluble tannin and ferrous tartrate in a buffered medium at pH 6.8. The spot test is a reliable and advantageous alternative technique because it uses fewer chemicals than the reference method. The study obtained good limits of detection (0.11 mg L−1), and precision (RSD = 0.9%), and at a 95% confidence level (paired t-test) no statistically significant difference between the results of either method was found.