Overview
ISO 3332:1975 specifies a titrimetric (volumetric) method after distillation for determining the ammoniacal nitrogen content of ammonium sulphate for industrial use. The method is based on displacing ammonia from a dissolved test sample with alkali, distilling the liberated ammonia into an excess of standard sulfuric acid, and back‑titrating the excess acid with standard sodium hydroxide using a mixed methyl red/methylene blue indicator.
Keywords: ISO 3332:1975, ammonium sulphate, ammoniacal nitrogen, titrimetric method, distillation, volumetric analysis, back‑titration.
Key topics and requirements
- Scope: Quantitative determination of ammoniacal nitrogen in industrial ammonium sulphate.
- Reagents (analytical grade):
- Sodium hydroxide (450 g/L) for distillation displacement.
- Standard volumetric sulfuric acid (0.5 N) for ammonia absorption.
- Standard volumetric sodium hydroxide (0.5 N) for back‑titration.
- Mixed indicator (methyl red + methylene blue in ethanol).
- Apparatus: Quantitative distillation assembly (distillation flask, splash head with dropping funnel, Liebig condenser, receiving conical flask ~500 ml); typical apparatus illustrated in the standard. Use anti‑bumping granules, silicone grease on joints and spring clamps.
- Sample & procedure essentials:
- Test portion: ~10.000 g (weigh to 0.001 g).
- Dissolve sample in water in a 1 000 ml distillation flask, add 20 ml of NaOH (450 g/L) via dropping funnel to displace ammonia.
- Distil; absorb ammonia in ~40 ml of 0.5 N H2SO4 (in receiving flask) diluted with water and indicator until receiving volume reaches ~250–300 ml.
- Back‑titrate the excess H2SO4 with 0.5 N NaOH to the indicator endpoint. Perform a simultaneous blank.
- Calculation: The mass of nitrogen corresponding to 1 ml of 0.5 N H2SO4 is 0.007004 g. Ammoniacal nitrogen (%) is calculated from the difference in titrant volumes (determination minus blank), the 0.007004 factor and the sample mass.
Applications and users
- Practical for quality control laboratories, fertilizer manufacturers, industrial chemical producers, incoming/outgoing goods inspection, and regulatory testing where accurate ammoniacal nitrogen measurement in ammonium sulphate is required.
- Useful for ensuring product conformity, specifying fertilizer N content, and troubleshooting production or storage issues that affect ammonia losses.
Related standards
ISO 3332 is part of a family of ISO methods for ammonium sulphate testing. Related standards include:
For implementation, follow the full ISO 3332:1975 text for exact procedural details, apparatus drawings and reporting requirements.
Open preview (PDF)Ammonium sulphate for industrial use — Determination of ammoniacal nitrogen content — Titrimetric method after distillation
