ISO 1388-7:1981

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.