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D5553-95 – Standard Test Method Technical Guide
📐 Scope, Significance, and Apparatus
This test method, designated D5553 −95 (Reapproved 2019) and developed under the jurisdiction of ASTM Committee D31 on Leather, provides a procedure for determining the unsaponifiable, nonvolatile (above 80°C) matter in sulfated oils. It is primarily intended for quality assurance purposes in the fats and oils industry. The values stated in SI units are regarded as the standard. This standard does not purport to address all safety concerns; it is the responsibility of the user to establish appropriate safety, health, and environmental practices prior to use.
The apparatus required includes a saponification flask equipped with an air condenser, 250-mL separatory funnels, and an electric hot plate. Key reagents include Ethyl Ether, Alcoholic Potassium Hydroxide solution (28 g/L), and Aqueous Potassium Hydroxide solution (28 g/L).
⚠️ Important Safety Precaution: Ethyl ether is highly volatile and extremely flammable. Saponification and extraction procedures must be conducted in a well-ventilated area or fume hood, away from all sources of ignition.
⚙️ Test Procedure and Reagent Preparation
Reagent Preparation: Prepare the alcoholic KOH solution by dissolving approximately 28 g of KOH in ethyl alcohol and diluting to 1 L (28 g/L). Prepare the aqueous KOH solution (28 g/L) in a similar manner using water.
Procedure: The test involves decomposing the sample with mineral acid to obtain desulfated fatty matter (as described in Test Methods D5350, D5351, and D5353). Accurately weigh 2 to 2.5 g of this desulfated fatty matter into the saponification flask. Add 25 mL of the alcoholic KOH solution and simmer the contents for 1 hour with occasional swirling, using an air condenser to prevent alcohol loss.
Extraction: Transfer the warm saponified mixture (approximately 30°C) to a 250-mL separatory funnel, washing the flask with a total of 50 mL of water. Rinse the saponification flask with 50 mL of ethyl ether and add it to the funnel. Shake vigorously for about 1 minute, and allow the layers to settle and clear. Draw off the lower layer into a second 250-mL separatory funnel and repeat the extraction twice more with 50 mL portions of ether.
💡 Technical Tip: Extracting the solution while it is still warm (~30°C) significantly improves the separation of the ether and aqueous (soap) layers. Shaking vigorously for a full minute is critical for ensuring complete extraction of the unsaponifiable matter.
📊 Key Measured Properties and Specifications
The test method relies on precise control of reagent concentrations and procedural parameters to ensure accurate results. The following tables summarize the critical specifications.