ISO 5379:2013

Overview

ISO 5379:2013 - "Starches and derived products - Determination of sulfur dioxide content - Acidimetric method and nephelometric method" specifies two validated analytical procedures for measuring sulfur dioxide (SO2) in starches and starch-derived products. The standard (second edition, 2013) defines the scope, required reagents and apparatus, stepwise procedures, calculation of results, quality checks and reporting rules for routine laboratory determinations.

Key topics and technical requirements

• Two methods specified
  • Acidimetric (entrainment + titration): SO2 is displaced from the sample by acid and nitrogen entrainment, absorbed in hydrogen peroxide, converted to sulfuric acid and titrated with standardized NaOH (or determined by iodine titration as a check).
  • Nephelometric: Used when titrant volumes are very small (practical limit thresholds specified); detects sulfate/barium sulfate turbidity using barium chloride/PVP reagent and measurement at 650 nm.
• Essential reagents and purity
  • Reagents must be analytical quality and sulfate-free (water, hydrogen peroxide solutions, hydrochloric acid, indicators, standardized NaOH and iodine solutions, Na2S2O5/EDTA standard).
  • Nephelometric reagents include polyvinylpyrrolidone (PVP), barium chloride and a mixed reagent with ethanol and sulfuric acid.
• Apparatus
  • Entrainment apparatus (Lieb/Zaccheri type) with round-bottom flask, condenser and two bubblers; ground-glass joints recommended.
  • Standard volumetric glassware, burettes, analytical balance, magnetic stirrer with heating, water bath (20 ±1 °C) and a spectrometer at 650 nm for nephelometry.
• Sampling and test portion
  • Test portion mass depends on expected SO2 (table provided). For high contents adjust to contain ≤10 mg SO2.
• Quality control
  • Check tests for entrainment apparatus and titration accuracy; minimize oxidation of standards (EDTA use).
  • Repeatability: difference between two determinations by same analyst ≤ 5% of mean. Reproducibility between labs ≤ 10% (ISO 5725-2 referenced).
• Decision rule
  • If titrant volume V < 5 mL (with 10 mmol/L NaOH) or < 0.5 mL (with 0.1 mol/L NaOH), the nephelometric method must be used. (For 100 g sample, 5 mL corresponds to ~16 mg SO2/kg.)

Applications and users

• Quality control and compliance testing in the starch production and food ingredient industries.
• Contract testing and food analysis laboratories monitoring sulfite/sulfur dioxide residues in starches, flours, dextrins and derived products.
• Regulatory bodies and R&D groups developing analytical protocols for food safety and labeling where SO2 limits apply.
• Useful for troubleshooting manufacturing processes where sulfiting agents are used.

Related standards

• ISO 1042 (volumetric flasks), ISO 648 (pipettes), ISO 385 (burettes), ISO 5725-2 (repeatability/reproducibility) - all cited within ISO 5379:2013 for equipment and precision guidance.

Keywords: ISO 5379:2013, sulfur dioxide determination, starches, acidimetric method, nephelometric method, SO2 analysis, entrainment apparatus, nephelometry, titration, food quality control.