ISO 1388-9:1981

Overview

ISO 1388-9:1981 specifies a titrimetric method after saponification for determining the esters content in ethanol for industrial use. Applicable to ethanol products with ester concentrations ranging from 0.005% to 0.15% (mass/mass), this standard outlines a precise chemical test to accurately quantify esters, expressed as ethyl acetate. The method involves boiling the test sample with excess sodium hydroxide solution to saponify the esters, followed by titrating the residual sodium hydroxide with hydrochloric acid in the presence of phenolphthalein indicator.

This international standard was developed by ISO Technical Committee ISO/TC 47 (Chemistry) and replaces the earlier ISO Recommendation R 1388-1970 as a technical revision.

Key Topics

• Scope and applicability: Suitable for industrial ethanol with esters content between 0.005% and 0.15% (m/m).
• Principle:
  • Saponification of esters by boiling with excess sodium hydroxide.
  • Determination of unreacted sodium hydroxide by titration with hydrochloric acid.
  • Use of phenolphthalein as indicator for endpoint detection.
• Apparatus:
  • Borosilicate conical flask (500 ml) with ground glass joint.
  • Water-cooled reflux condenser with adapter.
  • Standard laboratory glassware and titration equipment.
• Reagents:
  • Titrated sodium hydroxide solution (0.1 mol/l).
  • Titrated hydrochloric acid solution (0.1 mol/l).
  • Phenolphthalein ethanol solution (5 g/L).
  • Distilled water free of carbon dioxide.
• Procedure:
  • Sample aliquot is neutralized and saponified by reflux with sodium hydroxide.
  • The residual sodium hydroxide is back-titrated with hydrochloric acid.
  • A blank test is performed for accuracy.
• Calculation: Esters content expressed as percentage in mass of ethyl acetate, calculated based on titration volumes, sample mass density, and reagent concentrations.

Applications

ISO 1388-9:1981 is essential for quality control laboratories and industries utilizing industrial ethanol as a raw material or solvent where ester content affects performance and compliance. Typical applications include:

• Chemical manufacturing: Ensuring ester levels in ethanol meet process specifications.
• Pharmaceutical industry: Controlling purity of ethanol used in formulations.
• Food and beverage sector: Monitoring industrial ethanol additives.
• Environmental testing: Assessing ester contamination or degradation in ethanol batches.
• Regulatory compliance: Meeting international standards for ethanol purity and safety.

By providing a reliable, standardized titrimetric method, this standard helps manufacturers and laboratories maintain consistent quality and adhere to international industrial and safety regulations.

Related Standards

ISO 1388-9:1981 is part of a comprehensive series focusing on industrial ethanol testing methods:

• ISO 1388/1 – General principles including detection of alkalinity/acidity using phenolphthalein.
• ISO 1388/2 to ISO 1388/12 – Methods covering analysis of carbonyl compounds, aldehydes, methanol, hydrocarbons, furfural, and other impurities.
• ISO 1388/8 – Another titrimetric method for methanol determination.
• ISO 1388/10 to ISO 1388/12 – Additional procedures such as hydrocarbon evaluation by distillation and permanganate time determination.

Together, these standards enable comprehensive chemical characterization of industrial ethanol, ensuring product integrity and facilitating international trade.

Keywords: ISO 1388-9, industrial ethanol, esters content determination, titrimetric method, saponification, ethyl acetate, sodium hydroxide titration, hydrochloric acid, phenolphthalein indicator, quality control, chemical testing, ethanol purity standards.