Abstract:

At present, the five catechins in tea are commonly separated and determined according to the Chinese National
Standard GB/T 8313—2008, but the results of actual measurement show that the repeatability of this method is poor.
Moreover, different solvents are used in blank, standard and sample solutions, and standard substance is not be completely
dissolved in the solvent. In this study, an attempt was made to improve these drawbacks. Tea samples are extracted three
times at 70 ℃ with 10 mL of 70% preheated methanol solution, and then the extracts were combined and brought up to the
final volume with water. The analytes were determined using high performance liquid chromatograph (HPLC) with UV
detection at 278 nm. Mobile phase A was 1% acetic acid solution while mobile phase B was acetonitrile. The gradient elution
program used was as follows: 0–5 min, 95%–90% A; 5–15 min, 90% A; 15–20 min 90%–80% A; 20–25 min, 80%–90%
A; and 25–30 min, 90%–95% A. The results showed that the developed extraction technique that ensured that the solvents
of standard solution and samples were consistent allowed complete extraction of catechins, reducing errors arising from
the manual handling and having good repeatability. The relative standard deviations (RSDs) for 5 replicate determinations
were in the range of 0.75%–4.50%, and the degrees of separation were 0.58–4.35. Recoveries of spiked sample ranged from
81.4% to 113.0%, with RSDs between 1.21% and 7.71%.

Key words: tea, catechin, determination method, improvement