ISO 5381:1983

Overview

ISO 5381:1983 specifies a modified Karl Fischer method for determining the water content of starch hydrolysis products. The standard adapts the general Karl Fischer titration (ISO 760) by directly using a methanol/formamide solvent to improve extraction and measurement of water from starch derivatives and by‑products. It covers reagents, apparatus, sample preparation, titration procedure, calculations and reporting.

Key topics and requirements

• Scope: Determination of water in starch hydrolysis products using a stabilized Karl Fischer reagent (iodine, sulphur dioxide, pyridine and 2‑methoxyethanol) with methanol/formamide solvent.
• Reagents:
  • Stabilized Karl Fischer reagent (commercial or prepared per ISO 760).
  • Methanol/formamide solvent: mix 700 ml anhydrous methanol with 300 ml anhydrous formamide.
  • Sodium tartrate (Na2C4H4O6 · 2H2O) as standard for reagent standardization; check tartrate moisture by vacuum drying at 150 °C to constant mass (approx. 15.66% water).
• Apparatus:
  • Karl Fischer titrator or equivalent electrometric end‑point detection.
  • One‑mark pipettes, 10 ml syringe (special design for viscous samples), weighing tube for solids, analytical balance.
  • Platinum electrodes, titration vessel, burette (25 ml typical) and stirrer.
• Procedure:
  • Sample dispersion in methanol/formamide solvent to extract water.
  • Standardize reagent daily using sodium tartrate; perform titration until stable end‑point.
  • Carry out two determinations and use the mean if repeatability criteria are met.
• Calculations and quality criteria:
  • Water content calculated from reagent volume, reagent water equivalent (T) and sample mass (formula given in the standard).
  • Repeatability limits specified (e.g., difference ≤ 0.05 % for water < 1 %; progressively larger tolerances for higher water contents).

Applications and users

• Practical for quality control and moisture analysis in:
  • Food industry laboratories analyzing starch hydrolysates, syrups, dextrins and related ingredients.
  • Starch manufacturers, ingredient suppliers and R&D labs monitoring moisture content for stability and processing.
  • Analytical chemistry labs performing Karl Fischer titration for carbohydrate derivatives.
• Benefits: improved water extraction from viscous or hygroscopic starch products, reliable moisture quantification to support product specification, shelf‑life and processing control.

Related standards

• ISO 760 - Determination of water - Karl Fischer method (general method). ISO 5381 builds on and improves aspects of ISO 760 by specifying the methanol/formamide solvent and procedures specific to starch hydrolysis products.