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.
Open preview (PDF)Ethanol for industrial use — Methods of test — Part 2: Detection of alkalinity or determination of acidity to phenolphthalein
