Overview
ISO 20369:2009 specifies an analytical method for determining citrate content in materials used to produce wrappings for cigarette filters, cigarettes and other tobacco products. The standard defines an enzymatic spectrophotometric procedure that quantifies anhydrous citric acid (generally present as trisodium or tripotassium citrate) in wrapping materials to support quality control and regulatory testing in the tobacco supply chain.
Key topics and technical requirements
- Scope: Determination of citrate content in wrapping materials (cigarette paper, filter wrappings, other tobacco product wraps).
- Principle: Enzymatic conversion of citrate by citrate lyase to oxaloacetate + acetate; subsequent reactions with L‑MDH and L‑LDH consume NADH. The decrease in NADH is measured spectrophotometrically at 340 nm and is proportional to citrate concentration.
- Sample preparation: Typical extraction is ~1.0 g of conditioned wrapping material into 100 ml water, sonicated or stirred for 30 min and filtered.
- Reagents & test kits: Commercial enzymatic kits are recommended (example: Roche-Biopharm kit cited). Two reagent mixtures are used: (1) L‑MDH, L‑LDH, NADH and stabilizers; (2) citrate lyase. Storage conditions (e.g., +4 °C for 2 weeks or −20 °C for 4 weeks) are specified.
- Instrumentation & apparatus: Double‑beam spectrophotometer at 340 nm, 10 mm cuvets, pipettes (including piston‑operated and 20 µl), analytical balance, ultrasonic bath or magnetic stirrer.
- Performance limits & calibration: Absorbance difference (ΔA) should be ≥ 0.10 and ≤ 0.85 (dilute if higher). Calibration with citric acid standards (e.g., 50, 25, 12.5 mg/L). Calculation example: ρ (g/L) = 0.461 × ΔA for standard volumes. Results reported as percentage mass of anhydrous citric acid.
- Precision: Collaborative study data (nine laboratories) are reported in the standard for repeatability and reproducibility across sample citrate levels.
- Safety & reporting: Standard includes a safety warning and requires test reports to document sample identity, conditioning, moisture content (ISO 287), method reference, dates, and results.
Practical applications and who uses it
- Tobacco manufacturers and converters - quality control of cigarette paper and filter wrapping to ensure consistent burn rate and puff count.
- Analytical and contract testing laboratories - routine testing for citrate additives in wrapping materials.
- Regulatory agencies and compliance teams - verification of additive levels in tobacco product components.
- Material suppliers and R&D groups - formulation control and process validation for wrapping substrates.
Related standards and references
- ISO 187 (conditioning and testing atmosphere)
- ISO 287 (moisture content by oven-drying)
- ISO 3696 (water for analytical use)
- CORESTA Recommended Method No. 34 (related citrate determination method)
Keywords: ISO 20369:2009, citrate content determination, cigarette paper, wrapping materials, enzymatic method, citrate lyase, NADH spectrophotometry, tobacco product testing.
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