Overview
ISO 7108:1985 specifies a titrimetric (volumetric) method for the determination of ammonia content in ammonia solution for industrial use. The method is applicable to solutions containing up to 35% (m/m) ammonia and is intended for routine quality control and regulatory testing. The procedure requires introduction of a weighed test portion into a boric acid solution and titration with a standard sulfuric acid solution using methyl red as an indicator. WARNING: perform all operations in a well‑ventilated fume cupboard.
Key topics and technical requirements
- Scope and applicability
- Designed for industrial ammonia solutions up to 35% (m/m).
- Principle
- Ammonia is fixed in boric acid and then titrated with a standard sulfuric acid solution (c(1/2 H2SO4) = 1.000 mol/L) in the presence of methyl red.
- Reagents
- Boric acid solution (20 g/L)
- Standard volumetric sulfuric acid (1 mol/L)
- Methyl red indicator (1 g/L in ethanol)
- Use analytical‑grade reagents and distilled or equivalent water.
- Apparatus and sampling
- Thin spherical glass ampoule (example ~20 mm diameter with a capillary ~50 mm).
- Weigh ampoule to 0.0001 g precision before and after filling/sealing to obtain test portion mass.
- Procedure highlights
- Fill ampoule ~2/3 with sample, seal the capillary by flame, dry and reweigh to find mass of test portion.
- Break ampoule into a measured volume of boric acid solution (with methyl red) in a 750 mL conical flask, rinse washings into the flask and grind glass fragments.
- Titrate with sulfuric acid until the indicator changes from yellow to red.
- Calculation
- Ammonia content (percent by mass) is calculated from titration volume using the factor provided in the standard (0.01703 g NH3 per 1.00 mL of the specified sulfuric acid solution) and the mass of the test portion. Adjust if the titrant concentration differs from the specified value.
- Safety
- Conduct all steps in a fume hood; handle concentrated ammonia and acids with appropriate PPE.
Applications and users
- Typical users:
- Chemical manufacturers producing industrial ammonia solutions
- Quality control and analytical laboratories
- Industrial users (fertilizer producers, refrigeration maintenance, chemical processing)
- Regulatory and inspection bodies verifying product composition
- Practical uses:
- Routine batch testing to verify label claims and specification compliance
- Incoming goods inspection for raw ammonia solutions
- Process monitoring and troubleshooting in manufacturing lines
Related standards
- ISO 7108:1985 complements other ISO and national standards covering ammonia products and volumetric/analytical methods. Laboratories should consider relevant analytical quality and sampling standards when implementing this method.
Keywords: ISO 7108:1985, ammonia solution, ammonia content determination, titrimetric method, boric acid, sulfuric acid titration, methyl red indicator, volumetric analysis, industrial ammonia, analytical chemistry.
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