Overview
ISO 6374:1981 specifies an atomic absorption spectrometric procedure for the determination of phosphorus in natural and artificial cryolite and aluminium fluoride (AlF3) intended for industrial use. The method quantifies phosphorus indirectly by measuring the molybdenum absorbance (molybdenum hollow‑cathode lamp) after chemical conversion to an ammonium molybdophosphate complex and liquid‑liquid extraction.
Key topics and technical requirements
- Sample preparation: fusion of a dried test portion with sodium carbonate and boric acid in a platinum crucible, followed by dissolution in perchloric acid.
- Chemical conversion: formation of the ammonium molybdophosphate complex using ammonium molybdate reagent.
- Extraction: liquid‑liquid extraction of the molybdophosphate complex into isobutyl acetate and separation using 100 ml separating funnels.
- Instrumentation: atomic absorption spectrometer with acetylene/dinitrogen monoxide flame and a molybdenum hollow‑cathode lamp tuned to the 379.8 nm line.
- Calibration and range: calibration graph prepared from standard solutions (linear in the range about 0.1–2.0 µg P per mL); the method is applicable to products with phosphorus contents (expressed as P2O5) of approximately 5 to 60 mg/kg.
- Quality controls: simultaneous blank test, strict control of aspiration rates, and use of analytical‑grade reagents (double‑distilled water). Apparatus includes platinum crucible, separating funnels, shaker and AAS burner system.
- Result expression: phosphorus measured as P is converted to P2O5 using the factor 2.29; calculation formulas and reporting requirements are specified.
Practical applications and users
- Quality control and acceptance testing for cryolite and aluminium fluoride suppliers, smelters and raw‑material processors in the aluminium industry.
- Analytical chemistry and metallurgical laboratories performing phosphorus determination for product specification and contamination monitoring.
- Regulatory and standards organizations that require a traceable, validated method for reporting phosphorus content in industrial-grade fluorides.
- Useful where selective extraction and low-level determination of phosphorus are needed prior to AAS measurement.
Related standards
- ISO 1619 - Preparation and storage of cryolite samples
- ISO 2925 - Preparation and storage of aluminium fluoride samples
- ISO 5930 - Phosphorus determination (reduced molybdophosphate photometric method)
- Other ISO methods for related analytes (fluorine, iron, sodium, aluminium)
Keywords: ISO 6374, cryolite phosphorus determination, aluminium fluoride analysis, atomic absorption spectrometry, ammonium molybdophosphate extraction, molybdenum 379.8 nm.
Open preview (PDF)Cryolite, natural and artificial, and aluminium fluoride for industrial use — Determination of phosphorus content — Atomic absorption spectrometric method after extraction
