Overview
ISO 2211:1973 defines the standard procedure for measuring the colour of liquid chemical products in Hazen units, also known as the platinum-cobalt scale. This method is strictly applicable to clear, slightly coloured liquids that typically exhibit brownish-yellow hues. The procedure emphasizes visual comparison of the sample’s colour to standardized reference solutions, with results expressed in Hazen units. For routine control, instrumental methods such as comparators, calorimeters, or spectrophotometers may also be employed, provided these are verified against visual results. This international standard is developed and maintained by ISO Technical Committee ISO/TC 47, Chemistry.
Key Topics
- Visual Colour Measurement: ISO 2211 standardizes the process of visually comparing a liquid sample to pre-defined Hazen colour standards using simple laboratory apparatus like colorimetric tubes.
- Platinum-Cobalt Scale (Hazen Units): The Hazen unit expresses the colour intensity, calibrated using solutions containing known concentrations of platinum and cobalt compounds.
- Sample Applicability: The method is valid only for liquids that are clear and slightly coloured, matching the brownish-yellow colour of the platinum-cobalt reference scale.
- Instrumental Verification: Instruments such as comparators, colorimeters, or spectrophotometers can be used for colour measurement if they correlate exactly with traditional visual methods.
- Preparation and Storage of Standards: The standard outlines precise instructions for preparing and storing reference solutions to ensure reliability.
- Reporting Results: Results should clearly state the Hazen unit value. Any deviations or observations outside the standard method must be documented in the test report.
Applications
The ISO 2211:1973 standard is widely used in quality assurance, product specification, and compliance testing across the chemical and industrial sectors where the clarity and slight coloration of liquids are critical quality attributes. Key applications include:
- Chemical Manufacturing: Ensuring consistency of liquid chemicals such as solvents, reagents, and intermediates by monitoring colour levels.
- Water Treatment: Assessing colour in treated water or industrial effluents to meet regulatory and performance criteria.
- Pharmaceuticals & Cosmetics: Evaluating ingredient purity and batch-to-batch consistency where colour may indicate contamination or degradation.
- Laboratory Analysis: Providing a defined reference for visual and instrumental colour measurement in research and quality labs.
- Product Compliance: Satisfying customer and regulatory requirements for colour specifications in various industries using a globally recognized measurement system.
Related Standards
For broader context and complementary methodologies, the following related standards may be referenced:
- ISO 7887: Water quality - Examination and determination of colour
- ISO 6353: Reagents for chemical analysis - Methods for testing colorimetric performance
- ASTM D1209: Standard Test Method for Color of Clear Liquids (Platinum-Cobalt Scale)
- ISO/TC 47: International standards provided by the Chemistry technical committee, covering a wide range of methods for chemical product analysis.
Following the guidelines of ISO 2211:1973 ensures reliable, reproducible, and internationally recognized colour measurements for clear liquid chemical products, supporting both quality control and regulatory compliance processes.
Open preview (PDF)Liquid chemical products — Measurement of colour in Hazen units (platinum-cobalt scale)