Hard Paraffin

(Ph. Eur. monograph 1034)

Ph Eur

A purified mixture of solid saturated hydrocarbons generally obtained from petroleum. It may contain a suitable antioxidant.

Colourless or white or almost white mass; the melted substance is free from fluorescence in daylight.

Practically insoluble in water, freely soluble in methylene chloride, practically insoluble in ethanol (96 per cent).

First identification  A, C.

Second identification  B, C.

A. Infrared absorption spectrophotometry (2.2.24).

Comparison  hard paraffin CRS.

Preparation  Place about 2 mg on a sodium chloride plate, heat in an oven at 100 °C for 10 min, spread the melted substance with another sodium chloride plate and remove one of the plates.

B. Acidity or alkalinity (see Tests).

C. Melting point (2.2.16): 50 °C to 61 °C.

To 15 g add 30 mL of boiling water R and shake vigorously for 1 min. Allow to cool and to separate. To 10 mL of the aqueous layer add 0.1 mL of phenolphthalein solution R. The solution is colourless. Not more than 1.0 mL of 0.01 M sodium hydroxide is required to change the colour of the indicator to red. To a further 10 mL of the aqueous layer add 0.1 mL of methyl red solution R. The solution is yellow. Not more than 0.5 mL of 0.01 M hydrochloric acid is required to change the colour of the indicator to red.

Use reagents for ultraviolet absorption spectrophotometry. Dissolve 0.50 g in 25 mL of heptane R and place in a 125 mL separating funnel with unlubricated ground-glass parts (stopper, stopcock). Add 5.0 mL of dimethyl sulfoxide R. Shake vigorously for 1 min and allow to stand until 2 clear layers are formed. Transfer the lower layer to a 2nd separating funnel, add 2 mL of heptane R and shake the mixture vigorously. Allow to stand until 2 clear layers are formed. Separate the lower layer and measure its absorbance (2.2.25) between 265 nm and 420 nm using as the compensation liquid the clear lower layer obtained by vigorously shaking 5.0 mL of dimethyl sulfoxide R with 25 mL of heptane R for 1 min. Prepare a 7.0 mg/L reference solution of naphthalene R in dimethyl sulfoxide R and measure the absorbance of this solution at the absorption maximum at 278 nm using dimethyl sulfoxide R as the compensation liquid. At wavelengths from 265 nm to 420 nm, the absorbance of the test solution is not greater than one-third that of the reference solution at 278 nm.

Maximum 150 ppm.

Introduce 2.0 g of the melted substance to be examined into a 50 mL ground-glass-stoppered separating funnel. Add 30 mL of boiling distilled water R, shake vigorously for 1 min and filter.

Protected from light.

Ph Eur