Overview
ISO 1742:1980 specifies a vacuum oven method for the determination of dry matter in glucose syrups. The procedure applies regardless of syrup production method and is explicitly applicable to dried glucose syrup, solid glucose (starch sugar) and glucose syrups containing fructose (including isoglucose). The method uses a test portion mixed with kieselguhr (diatomaceous earth) and dried under reduced pressure at controlled temperature to produce reproducible dry-matter measurements useful for quality control and specification compliance.
Key Topics
- Principle: Dry a diluted test portion mixed with kieselguhr in a vacuum oven at 70 °C and pressure ≤ 34 mbar until constant mass is achieved.
- Sample preparation:
- Mix the laboratory sample well and weigh an 8–10 g test portion into a 100 ml beaker.
- Dilute with warm water and transfer quantitatively to a weighed drying dish containing ~30 g dried kieselguhr.
- Kieselguhr should be washed (acid then water), air-dried and oven-dried at 105 °C before use.
- Apparatus essentials:
- Analytical balance (0.001 g resolution)
- 100 ml beaker and inert metal or covered glass dish (≈75 mm deep, 90 mm diameter)
- Glass stirring rod
- Electrically heated vacuum oven capable of 70 ± 1 °C, uniform heat distribution and maintaining reduced pressure
- Vacuum pump able to reduce oven pressure to 34 mbar or less
- Drying train with silica gel and acid scrubber; desiccator with desiccant
- Drying schedule and constant mass criterion:
- Initial drying: 5 h at 70 ± 1 °C under ≤ 34 mbar with a slow air stream through the drying train
- After initial drying, crush the kieselguhr, return to oven for a further 10 h at same conditions
- Constant mass: loss after the second 5 h drying period should be ≤ 0.02% of the test portion mass
- If constant mass not reached after a total of 20 h, repeating the test is recommended (likely due to inadequate mixing)
- Replicates and reporting:
- Perform two determinations on the same laboratory sample
- Report method, operating conditions not specified in the standard, and any circumstances affecting results
Applications
- Routine quality control and specification verification of glucose syrups used in food, beverage and ingredient manufacturing
- Analysis of dried syrups, starch sugars and syrups with added fructose (including formulations defined as isoglucose)
- Establishing moisture content for storage, formulation and shelf-life assessment
- Lab-to-lab comparability where standardized vacuum-oven moisture methods are required
Related Standards
- ISO 1742:1980 is the technical revision replacing ISO Recommendation R 1742-1970 and was developed by ISO/TC 93 (Starch and derivatives).
- When implementing this method, consider other ISO and regional standards for carbohydrate analysis, moisture determination and equipment calibration to ensure traceability and compliance.
This standard provides a practical, validated procedure for accurate dry matter determination in glucose syrups. Adherence to prescribed temperatures, pressures, mixing with kieselguhr and the constant mass criterion is essential for reproducible results used in product quality control and specification management.
