Overview
ISO 1388-7:1981 specifies a photometric method for determining the methanol content in ethanol for industrial use. This international standard applies to ethanol samples with methanol concentrations between 0.01% and 0.20% (V/V). The method is based on the oxidation of methanol to formaldehyde, followed by a colorimetric reaction with chromotropic acid, producing a violet coloration measurable via photometry at approximately 570 nm wavelength.
Developed by ISO Technical Committee 47 (Chemistry), ISO 1388-7 forms part of a comprehensive series focused on test methods for ethanol used in industry. This standard replaces the earlier ISO Recommendation R 1388-1970, providing a revised and validated approach for assessing methanol content with high precision.
Key Topics
- Analytical principle: Methanol oxidized by potassium permanganate in phosphoric acid forms formaldehyde. Formaldehyde reacts with chromotropic acid producing a violet color.
- Measurement technique: Photometric absorbance measurement at 570 nm to quantify methanol concentration through color intensity.
- Range: Suitable for methanol concentrations between 0.01% and 0.20% by volume (V/V) in ethanol.
- Reagents: Use of potassium permanganate solution, chromotropic acid, disodium metabisulphite, and purified water ensures accuracy.
- Calibration: Standard methanol solutions are prepared and used to develop a calibration graph correlating absorbance to methanol concentration.
- Sample preparation: Test solutions are prepared by diluting a fixed volume of ethanol sample for consistent analysis.
- Quality control: Blank tests and purification procedures for reagents enhance result reliability.
Applications
- Industrial Ethanol Quality Control: Ensures methanol content in ethanol used for industrial purposes remains within specified limits for safety and regulatory compliance.
- Chemical Manufacturing: Accurate methanol determination safeguards production of ethanol-based solvents, pharmaceuticals, and chemical intermediates.
- Environmental and Safety Monitoring: Detection of methanol impurities helps minimize toxic exposure risks in manufacturing processes.
- Research and Development: Provides a validated analytical technique for laboratory analysis of ethanol purity and contamination levels.
- Trade and Compliance: Supports adherence to international specifications for ethanol quality, facilitating trade and product certification.
Related Standards
ISO 1388 is a multipart series addressing ethanol testing:
- ISO 1388-1: General methods, alkalinity, and acidity tests.
- ISO 1388-3 to ISO 1388-5: Determination of carbonyl compounds and aldehydes using photometric and titrimetric methods.
- ISO 1388-6: Test for miscibility with water.
- ISO 1388-8: Determination of higher methanol contents via visual methods.
- ISO 1388-9 to ISO 1388-12: Tests for esters, hydrocarbons, furfural, and permanganate time for overall ethanol quality assessment.
These complementary standards provide a comprehensive framework for analyzing the composition and properties of industrial ethanol, promoting uniform testing protocols globally.
Keywords: ISO 1388-7, methanol content, ethanol industrial use, photometric method, methanol determination, potassium permanganate oxidation, chromotropic acid, ethanol quality control, industrial ethanol testing, international standard ISO, spectrophotometric analysis, methanol impurities, ethanol purity test.
Open preview (PDF)Ethanol for industrial use — Methods of test — Part 7: Determination of methanol content (methanol contents between 0,01 and 0,20 % (V/V)) — Photometric method
