Overview
ISO 3391:1976 specifies a flame atomic absorption (FAA) method for determining the calcium content of natural and artificial cryolite. The procedure covers sample dissolution, matrix treatment to remove hydrofluoric acid, preparation of calibration (matching) solutions, and spectrophotometric measurement of calcium using a calcium hollow cathode lamp at the 422.7 nm line. This first-edition ISO method (1976) is intended for routine laboratory analysis and quality control of cryolite used in aluminium processing.
Key topics and technical requirements
- Scope: Determination of calcium in cryolite by flame atomic absorption spectrophotometry.
- Sample preparation: Dissolve a weighed test portion in concentrated sulphuric acid, heat until hydrofluoric acid has evaporated, then treat the residue with concentrated hydrochloric acid and dilute for measurement.
- Matrix modifiers/complexants: Use of lanthanum nitrate (or lanthanum chloride) or triethanolamine as matching reagents to minimize interference.
- Calibration graph: Prepare a series of standard matching solutions from certified calcium standard solutions and plot absorbance vs. mg Ca per 100 ml to obtain the calibration curve.
- Instrumentation: Atomic absorption spectrophotometer with acetylene / dinitrogen monoxide flame (or air-acetylene when perchloric acid is used), calcium hollow cathode lamp, and control of aspiration rate and flame oxidizing conditions.
- Measurement protocol: Include reagent blank, preliminary and bracketing measurements, and maintenance of constant aspiration. Calculate concentration (mg Ca/100 ml) and report results-optionally converted to CaO using the standard conversion factor provided.
- Reporting: Include method reference, results and expression, any anomalies, and any non-standard operations.
Applications and users
- Quality control and acceptance testing for cryolite suppliers and aluminium smelters.
- Analytical and metallurgical laboratories performing calcium content determination in raw materials.
- Research labs and regulatory bodies requiring standardized cryolite analysis for process control and material certification.
- Useful for anyone needing reliable atomic absorption procedures for trace/major element analysis in fluoride-containing matrices.
Related standards
- ISO 1619 - Preparation and storage of test samples for cryolite
- ISO 2366 / ISO 2830 - Determination of sodium and aluminium (flame/atomic absorption methods)
- ISO 1693 / ISO 1694 - Determination of fluorine and iron in cryolite
- Check these related ISO methods for comprehensive cryolite characterization and laboratory workflows.
Keywords: ISO 3391:1976, cryolite analysis, calcium determination, flame atomic absorption, calcium hollow cathode lamp, 422.7 nm, sample preparation, calibration graph, atomic absorption spectrophotometer.