ISO 3332:1975

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:

• ISO 2992 (iron content - photometric)
• ISO 2993 (free acidity - titrimetric)
• ISO 2994 (insoluble matter - gravimetric)
• ISO 3333 (copper content - photometric)
• ISO 3694 (chlorides - potentiometric)

For implementation, follow the full ISO 3332:1975 text for exact procedural details, apparatus drawings and reporting requirements.