01/2017:0496
GLYCEROL
Glycerolum
C3H8O3
Mr 92.1
[56-81-5]
DEFINITION
Propane-1,2,3-triol.
Content: 98.0 per cent m/m to 101.0 per cent m/m (anhydrous substance).
CHARACTERS
Aspect: syrupy liquid, unctuous to the touch, colourless or almost colourless, clear, very hygroscopic.
Solubility: miscible with water and with ethanol (96 per cent), slightly soluble in acetone, practically insoluble in fatty oils and in essential oils.
IDENTIFICATION
First identification: A, B.
Second identification: A, C, D.
A. Refractive index (see Tests).
B. Infrared absorption spectrophotometry ([url=]2.2.24[/url]).
Preparation: to 5 mL add 1 mL of [url=]water R[/url] and mix carefully.
Comparison: Ph. Eur. reference spectrum of glycerol (85 per cent).
C. Mix 1 mL with 0.5 mL of [url=]nitric acid R[/url]. Superimpose 0.5 mL of [url=]potassium dichromate solution R[/url]. A blue ring develops at the interface of the liquids. Within 10 min, the blue colour does not diffuse into the lower layer.
D. Heat 1 mL with 2 g of [url=]potassium hydrogen sulfate R[/url] in an evaporating dish. Vapours (acrolein) are evolved which blacken filter paper impregnated with [url=]alkaline potassium tetraiodomercurate solution R[/url].
TESTS
Solution S. Dilute 100.0 g to 200.0 mL with [url=]carbon dioxide-free water R[/url].
Appearance of solution. Solution S is clear ([url=]2.2.1[/url]). Dilute 10 mL of solution S to 25 mL with [url=]water R[/url]. The solution is colourless ([url=]2.2.2, Method II[/url]).
Acidity or alkalinity. To 50 mL of solution S add 0.5 mL of [url=]phenolphthalein solution R[/url]. The solution is colourless. Not more than 0.2 mL of [url=]0.1 M sodium hydroxide[/url] is required to change the colour of the indicator to pink.
Refractive index ([url=]2.2.6[/url]): 1.470 to 1.475.
Aldehydes: maximum 10 ppm.
Place 7.5 mL of solution S in a ground-glass-stoppered flask and add 7.5 mL of [url=]water R[/url] and 1.0 mL of [url=]decolorised pararosaniline solution R[/url]. Close the flask and allow to stand for 1 h at a temperature of 25 ± 1 °C. The absorbance ([url=]2.2.25[/url]) of the solution measured at 552 nm is not greater than that of a standard prepared at the same time and in the same manner using 7.5 mL of [url=]formaldehyde standard solution (5 ppm CH[/url][url=]2O) R[/url] and 7.5 mL of [url=]water R[/url]. The test is not valid unless the standard is pink.
Esters. Add 10.0 mL of [url=]0.1 M sodium hydroxide[/url] to the final solution obtained in the test for acidity or alkalinity. Boil under a reflux condenser for 5 min. Cool. Add 0.5 mL of [url=]phenolphthalein solution R[/url] and titrate with [url=]0.1 M hydrochloric acid[/url]. Not less than 8.0 mL of [url=]0.1 M hydrochloric acid[/url] is required to change the colour of the indicator.
Impurity A and related substances. Gas chromatography ([url=]2.2.28[/url]).
Test solution. Dilute 10.0 mL of solution S to 100.0 mL with [url=]water R[/url].
Reference solution (a). Dilute 10.0 g of [url=]glycerol R1[/url] to 20.0 mL with [url=]water R[/url]. Dilute 10.0 mL of the solution to 100.0 mL with [url=]water R[/url].
Reference solution (b). Dissolve 1.000 g of [url=]diethylene glycol R[/url] in [url=]water R[/url] and dilute to 100.0 mL with the same solvent.
Reference solution (c). Dilute 1.0 mL of reference solution (b) to 10.0 mL with reference solution (a). Dilute 1.0 mL of this solution to 20.0 mL with reference solution (a).
Reference solution (d). Mix 1.0 mL of the test solution and 5.0 mL of reference solution (b) and dilute to 100.0 mL with [url=]water R[/url]. Dilute 1.0 mL of this solution to 10.0 mL with [url=]water R[/url].
Reference solution (e). Dilute 5.0 mL of reference solution (b) to 100.0 mL with [url=]water R[/url].
Column:
– size: l = 30 m, Ø = 0.53 mm;
– stationary phase: 6 per cent polycyanopropylphenyl siloxane and 94 per cent of polydimethylsiloxane.
Carrier gas: [url=]helium for chromatography R[/url].
Split ratio: 1:10.
Linear velocity: 38 cm/s.
Temperature:
