Overview
ISO 7408:1983 is an international standard established by the International Organization for Standardization (ISO) that specifies a titrimetric method for determining the ammoniacal nitrogen content in fertilizers. This method is particularly designed for fertilizers containing substances such as urea or urea-aldehyde condensates, which release ammonia when treated with sodium hydroxide. The procedure ensures accurate measurement of ammoniacal nitrogen even in the presence of other compounds that could interfere by releasing ammonia.
The method involves entraining ammonia released from a moderately alkaline test mixture at ambient temperature using a strong air current into a standard volumetric sulfuric acid solution. The excess sulfuric acid is then back-titrated with sodium hydroxide to quantify the ammoniacal nitrogen content. This approach is critical for ensuring fertilizer quality and compliance with regulatory requirements.
Key Topics
- Scope: Applicable for fertilizers with substances releasing ammonia upon treatment with sodium hydroxide.
- Principle: Ammonia entrainment into sulfuric acid and back-titration with sodium hydroxide.
- Reagents and Apparatus:
- Standard volumetric sulfuric acid and sodium hydroxide solutions
- Nonyl alcohol as a foaming suppressant
- Mixed indicator solution (ethanolic methyl red and methylene blue)
- Entrainment equipment including double-necked bottle, washing bottles, flow meter, and air source
- Procedure Steps:
- Preparation of the sample and reagents
- Air bubbling through alkaline test mixture to entrain ammonia
- Titration of residual acid with sodium hydroxide to determine ammonia amount
- Concurrent blank tests for accuracy
- Calculation: Formula given to express ammoniacal nitrogen content as a percentage of nitrogen by mass.
- Precision: Repeatability (r) of 0.16% and reproducibility (R) of 0.71% nitrogen content, ensuring reliable interlaboratory results.
- Test Reporting: Includes reference to ISO 7408, results expressed as % nitrogen, and notes on any unusual findings or deviations.
Applications
This ISO 7408 titrimetric method is widely used by:
- Fertilizer manufacturers for quality control to verify the ammoniacal nitrogen content in products containing ammonia-releasing substances.
- Regulatory bodies and testing laboratories to ensure fertilizer compliance with safety and labeling standards.
- Agricultural researchers and chemists analyzing nitrogen availability and fertilizer composition.
- Environmental monitoring where accurate nitrogen content measurement is necessary for nutrient management.
By employing this standardized analytical procedure, stakeholders can ensure consistency, accuracy, and legal compliance in the production and use of nitrogenous fertilizers, directly impacting agricultural productivity and environmental protection.
Related Standards
ISO 7408 complements other international and regional standards regarding fertilizer analysis and nitrogen determination, such as:
- ISO/TC 134 series: Fertilizers and soil conditioners standards addressing various fertilizer characterization methods.
- ISO 3696: Water quality guidelines relevant for reagent and sample preparation.
- ISO 383: Standards for laboratory glassware including ground glass joints used in entrainment apparatus.
Adherence to ISO 7408 also supports compliance with national fertilizer regulations and harmonizes analytical testing protocols globally, facilitating trade and quality assurance.
Keywords: ISO 7408, ammoniacal nitrogen determination, fertilizers, titrimetric method, ammonia release, sodium hydroxide, volumetric analysis, fertilizer quality control, nitrogen content analysis, fertilizer standards.
Open preview (PDF)Fertilizers — Determination of ammoniacal nitrogen content in the presence of other substances which release ammonia when treated with sodium hydroxide — Titrimetric method
