Overview
ISO 6293-1:1996 specifies a colour‑indicator titration method for determining the saponification number of petroleum products. The standard defines the laboratory procedure to quantify the amount of constituents in a petroleum sample that will saponify under the test conditions, expressed as milligrams of KOH consumed per gram of sample. The method applies to materials with saponification numbers in the range 2 mg/g to 200 mg/g KOH and uses alcoholic potassium hydroxide, back‑titration with standard hydrochloric acid, and phenolphthalein as the end‑point indicator.
Key topics and requirements
- Scope and limits: Applicable to many petroleum products and lubricants with SN 2–200 mg/g KOH; results for used oils or products containing sulfur, phosphorus, halogens or certain additives require careful interpretation due to interferences.
- Principle: Sample is dissolved in butan‑2‑one, refluxed with a known excess of alcoholic KOH, then the excess alkali is back‑titrated with standard alcoholic HCl using phenolphthalein.
- Reagents: Specified reagents include alcoholic KOH (typically 0.5 mol/L), alcoholic HCl (typically 0.5 mol/L), ethanol (or specified alcohol mixtures), butan‑2‑one (methyl ethyl ketone), petroleum spirit and phenolphthalein neutralized indicator. Reagent standards are referenced to ISO 6353‑2/3 and water to ISO 3696.
- Apparatus & procedure: Requires reflux apparatus (alkali‑resistant conical flask with condenser), hotplate, burettes and precision balance. Reflux time is specified (30 min after reflux begins for routine tests), with a concurrent blank determination and hot back‑titration to the phenolphthalein end‑point.
- Calculation & reporting: Saponification number is calculated from the difference between sample and blank titration volumes, concentration of HCl, and sample mass. Reporting rules and rounding guidance are provided.
- Precision: The standard gives interlaboratory precision data (repeatability and reproducibility) and warns that strong coloration can impair end‑point detection.
Applications and users
- Quality control and chemical analysis laboratories in the petroleum, lubricant and additives industries.
- Producers and formulators of crankcase oils, turbine oils, insulating oils and waxes for assessing fatty acid/glyceride content or tracking degradation.
- Regulatory bodies and testing laboratories requiring a standardized volumetric method for routine saponification testing.
- Useful for troubleshooting additive-related interferences and for comparability of results across labs.
Related standards
Keywords: ISO 6293-1, saponification number, petroleum products, colour‑indicator titration, phenolphthalein, KOH titration, butan‑2‑one, petroleum spirit, precision, laboratory method.