ISO 1388-2:1981

Overview

ISO 1388-2:1981 specifies a simple, reproducible method for the detection of alkalinity or the determination of acidity (to phenolphthalein) in ethanol for industrial use. The procedure is applicable to products with acidities ≥ 0.0008% (m/m) and expresses acidity as a percentage by mass of acetic acid (CH3COOH). This part of the ISO 1388 series replaces the earlier ISO Recommendation R 1388-1970 and is intended for routine quality control and conformance testing.

Key topics and requirements

• Scope: applies to ethanol for industrial use with acidity ≥ 0.0008% (m/m).
• Principle: dilution of a test portion with carbon dioxide‑free water, assessment with phenolphthalein indicator, and titration with standard volumetric sodium hydroxide (NaOH) where required.
• Reagents:
  • Carbon dioxide‑free water (recently prepared)
  • Standard NaOH solution: c(NaOH) = 0.100 mol·L⁻¹ (note: correct if concentration differs)
  • Phenolphthalein: 5 g/L ethanolic solution
• Apparatus: routine laboratory glassware including a 500 mL conical flask with soda‑lime guard tube and a 10 mL burette graduated to 0.02 mL.
• Test portion and procedure:
  • Take 100.0 ± 0.1 mL laboratory sample.
  • Dilute in 100 mL CO2‑free water, add phenolphthalein, note alkalinity to phenolphthalein.
  • If acidic, titrate with standard NaOH until a pink endpoint persists ~15 s, with careful mixing after each addition.
• Result expression: acidity (as % mass acetic acid) calculated from the NaOH volume used (V′ in mL) and sample density Q (g/mL) using the formula provided in the standard:
  • Acidity (%) = (0.006 × V′) / Q
  • (0.006 g is the acetic acid equivalent per 1 mL of 0.100 mol·L⁻¹ NaOH)

Applications and users

• Practical uses: quality control, acceptance testing, batch release, and contractual verification of industrial ethanol where acidity/alkalinity affects downstream processes.
• Typical users:
  • Analytical and QC laboratories in chemical and ethanol production industries
  • Suppliers and purchasers performing incoming/outgoing inspection
  • Regulatory and standards bodies verifying compliance
  • R&D groups validating feedstock quality for chemical syntheses

Related standards

ISO 1388 is a multipart series on tests for industrial ethanol. Relevant parts include:

• ISO 1388-1 - General (sample handling, density)
• ISO 1388-3 to ISO 1388-12 - methods for carbonyls, methanol, esters, hydrocarbons, furfural, permanganate time, miscibility and more

Keywords: ISO 1388-2, ethanol for industrial use, acidity determination, alkalinity detection, phenolphthalein, NaOH titration, acetic acid percentage, industrial ethanol testing.