Polyglyceryl 3 Diisostearate


R = H, or CO–C17H35-iso

1,2,3-Propanetriol, homopolymer, diisooctadecanoate;    
Triglyceryl diisostearate     [63705-03-3].
Polyglyceryl 3 Diisostearate is a mixture of polyglyceryl diesters of mainly isostearic acid, obtained by esterification of polyglycerin and isostearic acid. The polyglycerin consists mainly of triglycerin.
•  B. It meets the requirements of the test for Content of Fatty Acids.
•  Content of Fatty Acids
0.5 N methanolic sodium hydroxide solution:  Dissolve 20 g of sodium hydroxide in 50 mL of water, and mix. Cool to room temperature, and add 950 mL of methanol.
Boron trifluoride–methanol solution:  Dissolve 14 g of boron trifluoride in methanol to make 100 mL, and mix well.1
Saturated sodium chloride solution:  Dissolve about 375 g of sodium chloride in water to make 1000 mL.
Standard solution:  Prepare the calibration ester mixture by mixing up each individual ester component (see Table 1). Dissolve 500 mg of the calibration ester mixture in n-heptane, and dilute with n-heptane to 50 mL.
Table 1
Component in the Calibration
Ester Mixture
USP Methyl Myristate RS (C14:0) 7
USP Methyl Palmitate RS (C16:0) 70
USP Methyl Stearate RS (C18:0) 23
a  Composition is proposed according to the relative composition of these three fatty acid groups in Polyglyceryl 3 Diisostearate.
Sample solution:  Introduce 100 mg of Polyglyceryl 3 Diisostearate into a 25-mL conical flask, fitted with a suitable water-cooled reflux condenser and a magnetic stir bar. Add 2 mL of 0.5 N methanolic sodium hydroxide solution, mix, and reflux for about 30 min. Add 2 mL of Boron trifluoride–methanol solution through the condenser, and reflux for about 30 min. Add 4 mL of n-heptane through the condenser, and reflux for 5 min. Cool, remove the condenser, add about 10 mL of Saturated sodium chloride solution, shake, add a quantity of Saturated sodium chloride solution to bring the upper layer up to the neck of the flask, and allow the layers to separate. Collect 2 mL of n-heptane layer (upper layer), wash with three quantities, each of 2 mL of water, and dry the n-heptane phase over anhydrous sodium sulfate.
Chromatographic system 
Mode:  GC
Detector:  Flame ionization
Column:  0.32-mm × 30-m fused-silica capillary column, 0.25-µm layer of phase G16
Detector:  250
Injection port:  240
Column:  See the temperature program table below.
Hold Time at Final
150 6 250 6
Carrier gas:  Nitrogen
Flow rate:  1.0–1.2 mL/min
Injection size:  1 µL
Injection type:  Split injection. Split ratio is about 1:80.
System suitability 
Sample:  Standard solution
[Note—See the relative retention time table below. ]
Name Relative
Methyl myristate 1.0
Methyl palmitate 1.4
Methyl stearate 1.8
Suitability requirements 
Resolution:  NLT 10 between the peaks due to methyl palmitate and methyl stearate
Relative standard deviation:  NMT 6.0% for the peak responses for palmitate and stearate
Samples:  Standard solution and Sample solution
Identify the fatty acid ester peaks in the chromatogram of the Sample solution by comparing the retention times of these peaks with those obtained in the chromatogram of the Standard solution, and measure the peak areas for all of the fatty acid ester peaks in the chromatogram obtained from the Sample solution.
Calculate the percentage of each fatty acid ester component in the test specimen:
Result = (rU/rT) × 100
rU== peak response for each individual fatty acid ester component
rT== sum of the peak responses, excluding the solvent peak, in the chromatogram obtained from the Sample solution
Acceptance criteria 
Sum of the contents of the fatty acids eluting between palmitic acid and stearic acid (excluding palmitic acid and stearic acid):  NLT 60.0%
Sum of the contents of myristic acid, palmitic acid, and stearic acid:  NMT 11.0%
Inorganic Impurities 
•  Residue on Ignition
Analysis:  Heat a silica crucible to redness for 30 min, allow to cool in a desiccator, and weigh. Evenly distribute about 1.0 g of Polyglyceryl 3 Diisostearate in the crucible and weigh. Dry at 100–105 for 1 h, and ignite in a muffle furnace at 600 ± 25, until the test substance is thoroughly charred. Perform the test for Residue on Ignition 281 on the residue obtained, starting with “Moisten the sample with a small amount (usually 1 mL) of sulfuric acid”.
Acceptance criteria:  NMT 0.5%
•  Heavy Metals, Method II 231: NMT 10 ppm
•  Acid Value
Analysis:  Accurately weigh (to within 0.1 mg) 5–10 g of Polyglyceryl 3 Diiostearate, add 10 mL of alcohol and 3 drops of phenolphthalein TS, and titrate with 0.1 N potassium hydroxide VS or 0.1 N sodium hydroxide VS until the solution remains faintly pink after shaking for 30 s. Follow the procedures for Fats and Fixed Oils, Acid Value 401 to perform the calculation.
Acceptance criteria:  NMT 3.0
•  Fats and Fixed Oils, Hydroxyl Value 401: 180–230, determined on a 0.25-g specimen
•  Iodine Value
Analysis:  Accurately weigh 3 g of Polyglyceryl 3 Diiostearate, transfer to a dry 250-mL flask with a ground-glass stopper, and add 25 mL of methylene chloride. Add 20 mL of the Wijs’ solution.2 Close the flask, and keep it in the dark for 1 h while shaking frequently. Perform the test in Fats and Fixed Oils 401 Iodine Value, starting with “Then add, in the order named, 30 mL of potassium iodide TS and 100 mL of water”.
Acceptance criteria:  NMT 3.0
•  Fats and Fixed Oils, Peroxide Value 401: NMT 6.0. Use 30 mL of a mixture of glacial acetic acid and methylene chloride (3:2) to replace the 30 mL of a mixture of glacial acetic acid and chloroform (3:2).
•  Water Determination, Method I 921: NMT 0.5%, determined on a 2.0-g specimen
•  Packaging and Storage: Preserve in tight, light-resistant containers, protected from heat and moisture.
•  USP Reference Standards 11
USP Methyl Myristate RS
USP Methyl Palmitate RS
USP Methyl Stearate RS
USP Polyglyceryl 3 Diisostearate RS

1  Boron trifluoride–methanol solution (14% in methanol) is also commercially available from Sigma, B-1252, or equivalent quality.
2  Wijs’ reagent RPE for analysis from Carlo Erba Reference 491902, Wijs’ solution from www.sigmaaldrich.com, or equivalent quality.
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