ISO 5440:1978

Overview

ISO 5440:1978 specifies a molybdovanadate spectrophotometric method for the determination of phosphate content in sodium hexafluorosilicate for industrial use. The method is applicable to phosphate levels expressed as phosphorus pentoxide (P2O5) in the range 0.005% to 0.05% (m/m). Test material is prepared from the residue remaining after the loss-in-mass determination described in ISO 5444.

Key steps in the method:

• Dissolve the test residue in dilute hydrochloric and nitric acid.
• Form the yellow molybdovanadate complex.
• Measure absorbance by spectrophotometry at about 420 nm.
• Calculate phosphate content (reported as % P2O5) from the measured absorbance using a calibration graph.

The standard includes safety notes: sodium hexafluorosilicate is poisonous if taken internally and dust inhalation should be avoided (use respirator and goggles).

Key topics and requirements

• Scope and applicability: Phosphate range 0.005–0.05% P2O5; test sample prepared from ISO 5444 residue.
• Reagents: Analytical-grade reagents including dilute HCl, dilute HNO3, and an ammonium molybdovanadate color reagent prepared from ammonium molybdate tetrahydrate and ammonium metavanadate in nitric acid.
• Calibration: Use a phosphate standard solution (prepared from potassium dihydrogen phosphate) to make a series of standard colorimetric solutions and plot a calibration graph of absorbance vs mg P2O5.
• Procedure: Weigh a dried test portion, digest with acid, dilute to volume, take aliquot, add molybdovanadate reagent, allow color development (≥10 min), and measure at ~420 nm in 1 cm cells.
• Quality control: Run a simultaneous blank, subtract blank absorbance, and use the calibration graph to determine phosphate mass; express results as % P2O5 per the formula and reporting requirements in the standard.
• Apparatus: Ordinary laboratory glassware and a spectrophotometer with 1 cm path length cells.

Applications and users

This ISO method is intended for:

• Chemical manufacturers and quality control laboratories handling sodium hexafluorosilicate (industrial grade).
• Analytical chemists performing routine phosphate determination and regulatory compliance testing.
• Suppliers and purchasers who require documented, reproducible methods for reporting phosphate (P2O5) content in the specified low concentration range.

Keywords: ISO 5440:1978, sodium hexafluorosilicate, phosphate content, molybdovanadate spectrophotometric method, P2O5, spectrophotometric measurement, analytical method.

Related standards

• ISO 5444 - Determination of loss in mass at 105 °C (sample preparation).
• ISO 4281 - Free acidity and sodium hexafluorosilicate content.
• ISO 5443 - Determination of iron content (1,10-phenanthroline method).
• ISO 5915 - Particle size distribution (sieving method).