ISO 2272:1989

Overview

ISO 2272:1989 specifies a spectrometric method for the determination of low contents of free glycerol in soaps. The technique uses molecular absorption spectrometry after chemical conversion of glycerol to a chromophore: soaps are decomposed by sulfuric acid, fatty acids are removed with petroleum ether, and free glycerol in the aqueous phase is oxidized by periodic acid to formaldehyde. Formaldehyde reacts with chromotropic acid to form an absorbing species measured at about 571 nm. The method is applicable to soaps with free glycerol content below 0.5% (w/w).

Key topics and technical requirements

• Scope: Intended for soaps with free glycerol < 0.5% (w/w).
• Principal steps:
  • Decomposition of soap by sulfuric acid.
  • Extraction of fatty acids with light petroleum (petroleum ether, distillation range 40–60 °C).
  • Oxidation of residual free glycerol in the aqueous phase using sodium metaperiodate (periodic acid).
  • Derivatization of formed formaldehyde with chromotropic acid in the presence of Sn(II) to produce a measurable chromophore.
  • Spectrometric measurement of absorbance at ~571 nm using a 1 cm cuvette.
• Reagents (examples from standard):
  • Petroleum ether (40–60 °C)
  • Sulfuric acid solutions (specified concentrations)
  • Sodium metaperiodate (~0.03 mol/L)
  • Chromotropic acid solution (prepared in strong sulfuric acid)
  • Tin(II) chloride solution
  • Glycerol standard solution (e.g., 25 mg/L)
• Apparatus:
  • Spectrometer (350–760 nm range) with continuous wavelength selector
  • Class A volumetric glassware (100 mL flasks, 5 mL burette)
  • 1 cm optical cuvettes, decanting funnels, water bath
• Quality-control elements:
  • Use of analytical-grade reagents and distilled water
  • Preparation of calibration solutions and a blank run
  • Calibration curve plotted from known glycerol microgram amounts
  • Measurement temperature control (15–25 °C) and verification of λmax

Applications and users

• Practical applications:
  • Quality control of soap production to monitor residual glycerol content
  • Product specification testing and batch release in manufacturing
  • Laboratory analysis during formulation development and process optimization
  • Regulatory or conformance testing when low glycerol content must be demonstrated
• Primary users:
  • Analytical chemists and QC laboratories in soap and surfactant industries
  • R&D teams developing soap formulations
  • Third‑party testing laboratories and standards organizations

Related standards

• ISO 8212 - Sampling and sampling techniques for soaps and detergents
• ISO 1042 - Volumetric flasks (laboratory glassware)
• ISO 385-1 - Burettes (laboratory glassware)
• ISO 6353-3 - Reagents for chemical analysis (specifications)

Keywords: ISO 2272, soaps, free glycerol, glycerol determination, molecular absorption spectrometry, chromotropic acid, periodic acid, petroleum ether, soap quality control.