(Ph. Eur. monograph 0240)
Preparation
Light Liquid Paraffin Eye Drops
DEFINITION
Purified mixture of liquid saturated hydrocarbons obtained from petroleum.
CHARACTERS
Appearance
Colourless, transparent, oily liquid, free from fluorescence in daylight.
Solubility
Practically insoluble in water, slightly soluble in ethanol (96 per cent), miscible with hydrocarbons.
IDENTIFICATION
First identification: A, C.
Second identification: B, C.
A. Infrared absorption spectrophotometry (2.2.24).
Comparison: Ph. Eur. reference spectrum of liquid paraffin.
B. In a test tube cautiously boil 1 mL with 1 mL of 0.1 M sodium hydroxide, with continuous shaking, for about 30 s. On cooling to room temperature, 2 phases separate. To the aqueous phase add 0.1 mL of phenolphthalein solution R. The solution becomes red.
C. Viscosity (see Tests).
TESTS
Acidity or alkalinity
To 10 mL add 20 mL of boiling water R and shake vigorously for 1 min. Separate the aqueous layer and filter. To 10 mL of the filtrate, add 0.1 mL of phenolphthalein solution R. The solution is colourless. Not more than 0.1 mL of 0.1 M sodium hydroxide is required to change the colour of the indicator to pink.
Relative density (2.2.5)
0.810 to 0.875.
Viscosity (2.2.9)
25 mPa·s to 80 mPa·s.
Polycyclic aromatic hydrocarbons
Use reagents for ultraviolet spectrophotometry.
Introduce 25.0 mL into a 125 mL separating funnel with unlubricated ground-glass parts (stopper, stopcock).
Add 25 mL of hexane R which has been previously shaken twice with one-fifth its volume of dimethyl sulfoxide R. Mix and 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 2 separating funnel, add 2 mL of hexane 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 260 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 hexane R for 1 min.
Prepare a 7.0 mg/L reference solution of naphthalene R in trimethylpentane R and measure the absorbance of the solution at the absorption maximum at 275 nm, using trimethylpentane R as the compensation liquid.
At no wavelength between 260 nm and 420 nm does the absorbance of the test solution exceed one-third that of the reference solution at 275 nm.
Readily carbonisable substances
Use a ground-glass-stoppered tube about 125 mm long and 18 mm in internal diameter, graduated at 5 mL and 10 mL; wash with hot water R (temperature at least 60 °C), acetone R, heptane R and finally with acetone R, dry at 100-110 °C. Cool in a desiccator. Introduce 5 mL of the substance to be examined and add 5 mL of nitrogen-free sulfuric acid R1. Insert the stopper and shake as vigorously as possible, in the longitudinal direction of the tube, for 5 s. Loosen the stopper, immediately place the tube in a water-bath, avoiding contact of the tube with the bottom or side of the bath, and heat for 10 min. After 2 min, 4 min, 6 min and 8 min, remove the tube from the bath and shake as vigorously as possible, in the longitudinal direction of the tube for 5 s. At the end of 10 min of heating, remove the tube from the water-bath and allow to stand for 10 min. Centrifuge at 2000 g for 5 min. The lower layer is not more intensely coloured (2.2.2, Method I) than a mixture of 0.5 mL of blue primary solution, 1.5 mL of red primary solution, 3.0 mL of yellow primary solution and 2 mL of a 10 g/L solution of hydrochloric acid R.
Solid paraffins
Dry a suitable quantity of the substance to be examined by heating at 100 °C for 2 h and cool in a desiccator over sulfuric acid R. Place in a glass tube with an internal diameter of about 25 mm, close the tube and immerse in a bath of iced water. After 4 h, the liquid is sufficiently clear for a black line, 0.5 mm wide, to be easily seen against a white background held vertically behind the tube.
STORAGE
Protected from light.
FUNCTIONALITY-RELATED CHARACTERISTICS
This section provides information on characteristics that are recognised as being relevant control parameters for one or more functions of the substance when used as an excipient (see chapter 5.15). Some of the characteristics described in the Functionality-related characteristics section may also be present in the mandatory part of the monograph since they also represent mandatory quality criteria. In such cases, a cross-reference to the tests described in the mandatory part is included in the Functionality-related characteristics section. Control of the characteristics can contribute to the quality of a medicinal product by improving the consistency of the manufacturing process and the performance of the medicinal product during use. Where control methods are cited, they are recognised as being suitable for the purpose, but other methods can also be used. Wherever results for a particular characteristic are reported, the control
method must be indicated.
The following characteristic may be relevant for light liquid paraffin used as emollient in ointments, as vehicle in eye preparations or as lubricant in tablets and capsules.
Viscosity
(see Tests).
