Edition: BP 2025 (Ph. Eur. 11.6 update)
Action and use
Stimulant laxative; emollient.
Preparation
Zinc and Castor Oil Ointment
DEFINITION
Fatty oil obtained by cold expression from the seeds of Ricinus communis L. A suitable antioxidant may be added.
PRODUCTION
During the expression step, the temperature of the oil must not exceed 50 °C.
CHARACTERS
Appearance
Clear at 40 °C, slightly yellow, viscous, hygroscopic liquid.
Solubility
Slightly soluble in light petroleum, miscible with ethanol (96 per cent) and with glacial acetic acid.
Relative density
About 0.958.
Refractive index
About 1.479.
IDENTIFICATION
First identification: B, C.
Second identification: A, B.
A. A mixture of 2 mL of the substance to be examined and 8 mL of ethanol (96 per cent) R is clear (2.2.1).
B. Specific absorbance (see Tests).
C. Composition of fatty acids (see Tests).
TESTS
Optical rotation (2.2.7)
+ 3.5° to + 6.0°.
Specific absorbance (2.2.25)
Maximum 0.7, determined at the absorption maximum at 270 nm.
To 1.00 g add ethanol (96 per cent) R and dilute to 100.0 mL with the same solvent.
Acid value (2.5.1)
Maximum 1.5.
Dissolve 5.00 g in 25 mL of the prescribed mixture of solvents.
Hydroxyl value (2.5.3, Method A)
Minimum 160.
Peroxide value (2.5.5, Method A)
Maximum 10.0.
Unsaponifiable matter (2.5.7)
Maximum 0.8 per cent, determined on 5.0 g.
Composition of fatty acids
Gas chromatography (2.4.22) with the following modifications. Use the mixture of calibrating substances in Table 2.4.22.-3.
Test solution Introduce 75 mg of the substance to be examined into a 10 mL centrifuge tube with a screw cap. Dissolve in 2 mL of 1,1-dimethylethyl methyl ether R1 with shaking and heat gently (50-60 °C). Add, while still warm, 1 mL of a 12 g/L solution of sodium R in anhydrous methanol R, prepared with the necessary precautions, and mix vigorously for at least 5 min. Add 5 mL of distilled water R and mix vigorously for about 30 s. Centrifuge for 15 min at 1500 g. Use the upper layer.
Reference solution Dissolve 50 mg of methyl ricinoleate CRS and 50 mg of methyl stearate CRS in 10.0 mL of 1,1- dimethylethyl methyl ether R1.
Column:
— material: fused silica;
— size: l = 30 m, Ø = 0.25 mm;
— stationary phase: macrogol 20 000 R (film thickness 0.25 µm).
Carrier gas helium for chromatography R. Flow rate 0.9 mL/min.
Split ratio 1:100.
Temperature:
| Time (min) | Temperature (°C) | |
| Column | 0 – 55 | 215 |
| Injection port | 250 | |
| Detector | 250 | |
Detection Flame ionisation.
Injection 1 µL.
System suitability:
— symmetry factor: 0.7 to 1.5 for the peak due to methyl stearate in the chromatogram obtained with the test solution.
Calculate the percentage content of each fatty acid by the normalisation procedure.
Correct the area of the peak due to methyl ricinoleate, by multiplying by a factor R calculated using the following expression:
(m1×A2)/(A1×m2)
m1 = mass of methyl ricinoleate in the reference solution;
m2 = mass of methyl stearate in the reference solution;
A1 = area of the peak due to methyl ricinoleate in the chromatogram obtained with the reference solution;
A2 = area of the peak due to methyl stearate in the chromatogram obtained with the reference solution.
Composition of the fatty-acid fraction of the oil:
— palmitic acid: maximum 2.0 per cent;
— stearic acid: maximum 2.5 per cent;
— oleic acid and isomer : 2.5 per cent to 6.0 per cent;
— linoleic acid : 2.5 per cent to 7.0 per cent;
— linolenic acid : maximum 1.0 per cent;
— eicosenoic acid : maximum 1.0 per cent;
— ricinoleic acid : 85.0 per cent to 92.0 per cent;
— any other fatty acid: for each fatty acid, maximum 1.0 per cent.
Water (2.5.32)
Maximum 0.3 per cent, determined on 1.00 g.
STORAGE
In an airtight, well-filled container, protected from light.
