Overview
ISO 14502-2:2005 specifies a validated high-performance liquid chromatography (HPLC) method for determining the total catechin content in tea by summing individual catechins. The method is designed primarily for green tea (leaf and instant) and - with stated precision limitations - can be applied to black tea. The standard also allows determination of gallic acid, caffeine, theogallin and theaflavins using the same HPLC procedure.
Key topics and technical requirements
- Analytical principle: Extraction of catechins followed by separation on a phenyl-bonded HPLC column with gradient elution and UV detection at 278 nm.
- Sample preparation:
- Leaf tea: extraction with 70% methanol at 70 °C.
- Instant tea: dissolution in hot water with 10% acetonitrile (stabilizing solution containing EDTA and ascorbic acid).
- Reagents and mobile phases: methanol, acetonitrile, glacial acetic acid, EDTA, ascorbic acid and Grade 1 water. Mobile phases include low- and high-acetonitrile compositions with EDTA and acetic acid (filtered through 0.45 µm).
- Standards and calibration:
- Use of individual catechin external standards (with known purity and moisture) for direct quantitation.
- Alternative: caffeine as external standard combined with consensus Relative Response Factors (RRFs) for individual catechins (from interlaboratory studies).
- Apparatus & conditions: analytical balances, water bath (70 ±1 °C), centrifuge, vortex mixer, 0.45 µm membrane filters, HPLC system with proper column.
- Quality/performance: method precision data (repeatability and reproducibility) and interlaboratory test results are provided (see Annex A). Safety precautions for handling organic solvents are specified.
Applications and who uses this standard
- Tea manufacturers: quality control of catechin content for product specifications and process monitoring.
- Food testing laboratories: routine analysis of green and instant tea, and limited application to black tea.
- Regulatory agencies and import/export authorities: verification of label claims and compliance with food standards.
- Research and nutrition science: quantifying catechins for studies on health benefits, formulation and bioactive content.
- Certification bodies and commodity traders: authentication, grading and value assessment based on polyphenol profile.
Related standards
- ISO 14502-1 - Total polyphenols in tea: colorimetric method (Folin–Ciocalteu).
- ISO 1572 - Preparation of ground tea sample of known dry matter.
- ISO 3696 - Water for analytical laboratory use.
- ISO 7513 - Moisture determination in instant tea.
Keywords: ISO 14502-2:2005, catechins, HPLC method, green tea analysis, tea quality control, gallic acid, caffeine, high-performance liquid chromatography.
Open preview (PDF)Determination of substances characteristic of green and black tea — Part 2: Content of catechins in green tea — Method using high-performance liquid chromatography
