สารบัญ

Thai name  น้ำมันละหุ่ง (NAM MAN LAHUNG)

Category  Purgative; emollient.

Castor Oil is the fixed oil obtained by cold expression from the seeds of Ricinus communis L. (Family Euphorbiaceae), and refined. The expressed oil is steamed to coagulate proteins and, after filtration, is usually bleached by exposure to the sun or by chemical means.

Origin of plant  Castor Oil-yielding plant is native to tropical northeast and east Africa.

Constituents  Castor Oil contains mainly ricinoleic acid and other minor acids such as stearic, palmitic, and oleic acids. The predominant triglyceride component is triricinolein.

Description  Clear, almost colourless or slightly yellow, viscid liquid; odour, very slight, free from foreign and rancid; taste, bland and characteristic.

Solubility  Slightly soluble in petroleum ether, miscible with ethanol, and with glacial acetic acid.

Packaging and storage  Castor Oil shall be kept in well-filled, tightly closed containers, protected from light, and stored at a temperature not exceeding 25º.

Labelling  The label states whether the contents are suitable for use in the manufacture of parenteral preparations.

Identification of fixed oils by thin-layer chromatography  Carry out the test as described in Appendix==.

       Results  The chromatogram obtained is similar to the corresponding chromatogram shown in the figure.

Light absorption  The absorbance of a 1.0 per cent w/v solution in ethanol, determined at the maximum at about 270 nm, is between 0.7 and 1.5 (Appendix 2.2). 

Specific gravity  0.953 to 0.965 (Appendix 4.9).

Refractive index  1.477 to 1.481, at 20° (Appendix 4.7).

Optical rotation  +3.5 to +6.0, at 20° (Appendix 4.8).

Acid value  Not more than 2.0 (Appendix 5.4); dissolve 5 g in 25 mL of the prescribed mixture of solvents.

Hydroxyl value  160 to 168 when determined by the following method.
      Transfer 2 g, accurately weighed, to a glass-stoppered, 250-mL conical flask, add 5.0 mL of a freshly prepared mixture of 1 volume of acetic anhydride and 3 volumes of pyridine, and swirl to mix. Connect the flask to a reflux condenser, and heat on s steam-bath for 1 hour. Add 10 mL of water through the condenser, swirl to mix, heat on a steam-bath for an additional 10 minutes, and allow to cool to room temperature. Add through the condenser 15 mL or 1-butanol that previously has been neutralized to phenolphthalein, remove the condenser, and wash the tip of the condenser and the sides of the flask with an additional 10 mL of neutralized l-butanol. Add 1 mL of phenolphthalein TS, and titrate with 0.5 M ethanolic potassium hydroxide VS to faint pink end-point. Perform a blank determination on a 5.0-mL portion of the acetic anhydride-pyridine mixture. To determine the amount of free acid in Castor Oil, weigh accurately 10 g into a 250-mL conical flask, add 10 mL of pyridine that previously has been neutralized to phenolphthalein TS, swirl to mix, add 1 mL phenolphthalein TS, and titrate with 0.5 M ethanolic potassium hydroxide VS to a faint pink end-point. Calculate the hydroxyl value by the formula as follows:

Hydroxyl Value = 56.1 M[A + (BW/D) – C]/W

where         M  =  the molarity determined for the ethanolic potassium hydroxide solution

                   A   = the volume, in mL, of 0.5 M ethanolic potassium hydroxide VS consumed by the blank,

                   B    = the volume, in mL, consumed in the free-acid titration,

                   W  = the weight, in g, of the oil taken,

                   D   = the weight, in g, of the oil used in the free-acid titration, and

                   C   = the volume, in mL, consumed in the sample titration.

Peroxide value  Not more than 5.0 (Appendix 5.12).

Saponification value  176 to 187 (Appendix 5.7).

Unsaponifiable matter  Not more than 0.8 per cent w/w (Method II, Appendix 5.8).

Composition of fatty acids Carry out the test as described in the “Gas Chromatography” (Appendix 3.4).

Standard solution  Dissolve about 50 mg of Methyl Ricinoleate RS and 50 mg of Methyl Stearate RS, accurately weighed, in 10.0 mL of 1,1-dimethylethyl methyl ether.

      Test solution  Transfer about 75 mg of the sample, accurately weighed, to a screw-capped, centrifuge tube. Dissolve in 2 mL of 1,1-dimethylethyl methyl ether with shaking and heat at 50 to 60. Add, while still warm, 1 mL of a 1.2 per cent w/v solution of sodium in anhydrous methanol, prepared with the necessary precautions, and shake vigorously for at least 5 minutes. Add 5 mL of distilled water and shake vigorously for 30 seconds. Centrifuge at 1500  g for 15 minutes. Use the upper layer.

      Chromatographic system

DETECTOR  Flame ionization.

COLUMN A fused-silica capillary column (30 m × 0.25 mm) packed with macrogol 20,000 (0.25 µm). 

TEMPERATURE

Column  215°

Injection port  250°

Detector  250°

CARRIER GAS  Helium.

FLOW RATE  0.9 mL per minute.

SPLIT RATIO  1:100

      System suitability

            SAMPLE  Test solution.

      Suitability requirements

           SYMMETRY FACTOR  0.7 to 1.5 for the methyl stearate peak. 

       Procedure  Separately inject equal volumes (about 1 µL) of Standard solution and Test solution into the chromatograph, and record the chromatograms.  Identify the peak due to the fatty acid ester peaks in the chromatogram of the Test solution by comparing the retention times of these peaks with those in the chromatogram of the Standard solution, and measure the peak areas for all of the fatty acid ester peaks in the chromatogram from the Test solution.

Calculation  Calculate the percentage content of the components of Castor Oil taken by normalization procedure. 

Limits  Castor Oil exhibits the composition profiles of fatty acids in Table 1, except for ricinoleic acid having a limit of 85.0 to 92.0 per cent. The limit for each unidentified fatty acids is not more than 1.0 per cent.

Table 1

Other requirements  Castor Oil intended for parenteral administration complies with the following additional requirements.

Water  Not more than 0.2 per cent w/w (Karl Fischer Method, Appendix 4.12); use 1 g.

Bacterial endotoxins  When tested as described in the “Test for Bacterial Endotoxins” (Appendix 8.5), it contains not more than the requirement under the relevant dosage form monograph(s) in which Castor Oil is used can be met. Where the label states that Castor Oil must be subjected to further processing during the preparation of parenteral dosage forms, the level of bacterial endotoxins is such that the requirement under the relevant dosage form monograph(s) in which Castor Oil is used can be met.