ISO 1388-4:1981

Overview

ISO 1388-4:1981 specifies a titrimetric method for estimating the content of carbonyl compounds present in moderate amounts in industrial ethanol. The method is applicable when carbonyl content, expressed as acetaldehyde, is ≥ 0.01% (m/m). It is designed for routine use in quality control and commercial testing and determines only those carbonyls that react under the specified conditions.

The analytical principle is the reaction of hydroxylammonium chloride with carbonyl compounds in a test portion, followed by titration of the hydrochloric acid formed with a standard sodium hydroxide (NaOH) volumetric solution. Bromophenol blue is used as the end-point indicator.

Key Topics

• Scope and applicability

  • Method intended for industrial ethanol samples with carbonyls ≥ 0.01% (m/m).
  • Detects only carbonyls reactive under the prescribed conditions; intended for routine commercial analysis.

• Analytical principle

  • Reaction of hydroxylammonium chloride with carbonyl compounds to form hydrochloric acid.
  • Titration of the acid with standard NaOH solution using bromophenol blue as indicator.

• Reagents and typical materials (as specified in the standard)

  • Hydroxylammonium chloride reagent prepared in ethanol/water and heated as described.
  • Standardized NaOH solution (c(NaOH) = 0.100 mol/L recommended in the document).
  • Bromophenol blue indicator in ethanolic solution.
  • Common laboratory glassware, e.g., 150 mL conical flasks with ground stoppers.

• Procedure highlights

  • A measured test portion is treated with indicator and adjusted to the colour of a blank.
  • Hydroxylammonium chloride reagent is added, samples are heated for a prescribed time, cooled and titrated with NaOH until the endpoint colour matches the blank.
  • Results are calculated and reported as percent by mass of acetaldehyde (CH3CHO), based on titration volume and reagent concentration.

Applications

• Quality control of industrial ethanol production and supply.
• Routine compliance testing for manufacturers, distributors and end-users where carbonyl impurity monitoring is required.
• Useful in commercial laboratories performing batch release, incoming inspection or periodic verification of ethanol purity.

Related Standards

ISO 1388 is a multipart series for industrial ethanol testing. Relevant related documents include:

• ISO 1388/1 – Generalities and related procedures.
• ISO 1388/3 – Photometric method for low carbonyl contents.
• ISO 1388/5 – Calorimetric visual methods for aldehyde determination.
• Other parts in the ISO 1388 series covering methanol, esters, hydrocarbons and other characteristic tests.

Practical value: ISO 1388-4:1981 provides a validated, repeatable titrimetric procedure that laboratories can use for reliable monitoring of moderate carbonyl contamination in ethanol, supporting product quality assurance and regulatory conformity.