Determination of Glycerol (Glycerin) Content of Soap

This procedure is for the determination of Glycerol content through Sodium meta-periodate. The method applies to soap and soap noodles or the determination of glycerol content titrimetric method.

2. APPARATUS

A suitable pH meter was calibrated on buffers 9.2 & 7.0. One-pan balance weighing to nearest 10 mg which will weigh up to 500g or more. Filter paper no 54

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*All equipment should be calibrated and functionality checks are done showing satisfactory performance of equipment

3. REAGENTS

Sodium meta periodate

solution. Standardized against

Sodium hydroxide 0.1N solution, standardized

Sodium hydroxide solution 25% approx.

Sulphuric Acid 20% approx.

Ethyl alcohol

Ethylene Glycol

Buffer solutions 9.2, 7.0, 4.0.

*All analytical pure grade

4. Procedure 

4.1 Weigh 5.0 gr to ± .0001 gr well-mixed sample into a 100 ml neat and dry beaker.

4.2 Add 80 ml distilled water, and a few carborundum pieces, and dissolve in a steam bath.

4.3 Add a few drops of methyl orange 3 ml of 20% H2SO4 and 3 ml alcohol. Immerse the beaker into a steam bath or heat on a hot plate. DO NOT LEAVE BEAKER UNATTENDED.

4.4 When the fatty acid layer is clear, filter through a wet filter paper # 54. Wash the beaker and filter paper with hot distilled water.

4.6 Add two drops of methyl orange indicator, a few carborundum pieces, and acidify with 20% H2SO4.

Boil for 5 minutes (VOLUME MUST NOT REDUCE BELOW 50-75 ml). Cover with a watch glass and cool down to R.T.

4.7 Standardize pH meter with pH 9.2 buffer. Run a blank with an equal volume of distilled water as that of a sample. Neutralize the sample and blank to pH 8.0 ± with NaOH (initially use 25% NaOH and near end use 0.1 IN NaOH).

4.8 Add 50 ml sodium meta periodate solution with 50 ml bulbed pipette, cover with a watch glass and immediately place in the dark for 30 ± 1minutes.

4.9 After 30 minutes remove from dark and add 10 ml of 50% ethylene glycol solution by a cylinder. Swirl gently, and cover with a watch glass to keep in the dark for 20 minutes ± 1 minute.

4.10 Wash the watch glass into a beaker and titrate contents against 0.1N NaOH to endpoint pH 8.0 ±1 for the sample beaker and to 6.5 ± 1 pH for the blank.

5. Calculation Of Glycerine Content. 

% Glycerol = (Volume used for sample - Volume used for Blank) x N x 9,209/W