Overview
ISO 22590:2020 - Traditional Chinese medicine - Determination of sulfur dioxide in natural products by titration - defines a standardized titration-based method to quantify sulfur dioxide (SO2) residues in natural products used in traditional Chinese medicine (TCM). The standard covers required apparatus, reagents, sampling and preservation, the test procedure, and the calculation for reporting results (mg/kg). It applies to plant- and animal-derived Chinese materia medica and decoction pieces, but not to mineral materials.
Key topics and technical requirements
- Scope and purpose: Measurement of sulfur dioxide residue in TCM natural products for quality control and safety assessment.
- Apparatus: Typical lab glassware including a three‑neck round‑bottom flask, separatory funnel, condenser, test tube and an electronic balance (minimum 0.1 mg).
- Reagents: Analytical grade/distilled water; indicators and chemicals such as bromophenol blue, hydrochloric acid, hydrogen peroxide (3 %), and 0.10 mol/L sodium hydroxide (standard titrant).
- Sampling & sample prep: Requirements for sample labelling, drying, powdering and short‑term storage (cool, dry, avoid sunlight). Timely pre‑treatment and refrigerated storage when immediate analysis is not possible.
- Test procedure (summary): CO2 purge of apparatus, addition of H2O2 and indicator, acidification of the sample to release SO2, boiling/distillation under CO2 stream, collection and acid‑base titration with NaOH, and blank titration.
- Calculation: Reported as mg/kg. The standard provides the calculation formula:
Sulfur dioxide (mg/kg) = 32 030 × (V1 − V2) × (n / m)
where V1 = titrant volume (test), V2 = titrant volume (blank), n = molarity of NaOH, m = sample mass (g).
- Informative annexes: Annex A lists national/regional limits and risk‑based calculations (WHO/USEPA references); Annex B describes a validated gas‑chromatography alternative; Annex C compares acid‑base titration practices internationally.
Applications
- Routine quality control testing of Chinese materia medica and decoction pieces to detect sulfur dioxide residues.
- Regulatory compliance monitoring against national MRLs and WHO/FAO guidance.
- Safety and exposure assessment using ADI and target hazard quotient approaches cited in Annex A.
- Method validation and comparison with gas chromatography for laboratories seeking higher sensitivity or confirmatory analysis.
Who should use this standard
- TCM manufacturers and raw material suppliers
- Independent analytical and pharmaceutical testing laboratories
- Regulatory agencies and public health bodies overseeing herbal product safety
- Quality assurance/quality control (QA/QC) teams and researchers working on herbal pharmacopoeia standards
Related standards and references
- Annex B (ISO 22590) - gas chromatography method for SO2 (informative alternative)
- Annex C (ISO 22590) - international comparison of acid‑base titration practices
- ISO/TC 249 (Traditional Chinese medicine) developed the document; national guidance (WHO, USEPA) and pharmacopoeial references are cited for risk assessment and MRL context.
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