Overview
ISO 7109:1985 specifies a simple, reproducible gravimetric method to determine the residue after evaporation of industrial ammonia solutions. The test evaporates a measured portion of sample in a tared platinum dish, dries the remaining residue at 105 ± 2 °C, and reports the residue mass as mg/kg. The method is applicable to ammonia solutions containing not more than 35% (m/m) ammonia and is intended for routine quality control and specification testing.
Key topics and requirements
- Scope: Determines non-volatile residue after evaporation for industrial ammonia solutions up to 35% (m/m).
- Safety: Operations must be carried out in a well‑ventilated fume cupboard due to ammonia vapors.
- Apparatus: Ordinary laboratory equipment including a tared platinum dish (~75 mm diameter), a 500 ml one‑mark volumetric flask for the test portion, and an electric oven maintainable at 105 ± 2 °C.
- Procedure:
- Prepare a test portion by filling a 500 ml volumetric flask with the laboratory sample.
- Weigh the dried, tared platinum dish to 0.0001 g accuracy.
- Pour a measured volume into the dish and evaporate to dryness on a boiling water bath in a fume cupboard, adding more sample until all liquid is removed.
- Dry the dish in the oven at 105 ± 2 °C (minimum 30 min), cool in a desiccator, and weigh the residue.
- Calculation: Residue (mg/kg) is calculated as:
- Residue = ((m1 − m0) × 10^6) / (V × Q)
- where m0 = mass of empty dish (g), m1 = mass of dish + residue (g), V = volume of test portion (mL), Q = density of sample (g/mL).
- Reference: The standard cites ISO documents for determination of density (ISO 750 / ISO 758 are referenced in the text).
Applications and users
ISO 7109 is used by:
- Chemical manufacturers producing industrial ammonia solutions for quality-control release testing.
- Analytical laboratories performing routine gravimetric analysis of ammonia products.
- Regulatory and inspection laboratories verifying product conformity to specifications.
- Process and QC engineers who need a standardized method to quantify non‑volatile residues that can affect downstream processes, equipment scaling, or product purity.
Practical applications include batch acceptance testing, trend monitoring of impurities, and specification verification for suppliers and purchasers of industrial ammonia.
Related standards
- ISO 750 / ISO 758 (density determination) - referenced for sample density Q used in calculations.
- Other ISO chemical product methods prepared by ISO/TC 47 (Chemistry) for complementary analyses of industrial liquids.
Keywords: ISO 7109, ammonia solution, residue after evaporation, gravimetric method, 105 °C, industrial ammonia, platinum dish, analytical method, quality control.
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