Castor Oil
(kas' tor oyl).
DEFINITION
Castor Oil is the fixed oil obtained from the seed of Ricinus communis L. (Fam. Euphorbiaceae). It contains no added substances.
IMPURITIES
•  Heavy Metals, Method II 231: NMT 10 ppm
SPECIFIC TESTS
•  Specific Gravity 841: 0.957–0.961
•  Distinction from Most Other Fixed Oils: It is only partly soluble in solvent hexane (distinction from most other fixed oils), but it yields a clear liquid with an equal volume of alcohol (foreign fixed oils).
•  Fats and Fixed Oils, Free Fatty Acids 401: The free fatty acids in 10 g require NMT 3.5 mL of 0.10 N sodium hydroxide for neutralization.
•  Fats and Fixed Oils, Hydroxyl Value 401
Free acid determination 
Sample:   10 g
Titrimetric system  
Mode:  Direct titration
Titrant:  0.5 N alcoholic potassium hydroxide VS
Endpoint detection:  Visual
Analysis:  Transfer the Sample to a 250-mL conical flask, add 10 mL of pyridine that has been neutralized previously to phenolphthalein, and swirl to mix. Add 1 mL of phenolphthalein TS, and titrate with Titrant to a faint pink endpoint. Record the volume of Titrant consumed (VA).
Hydroxyl value determination 
Sample:  2 g
Blank:   5.0 mL of a freshly prepared mixture of 1 volume of acetic anhydride and 3 volumes of pyridine
Titrimetric system 
Mode:   Residual titration
Titrant:  0.5 N alcoholic potassium hydroxide VS
Endpoint detection:  Visual
Analysis:  Transfer the Sample 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 a steam bath for 2 h. Add 10 mL of water through the condenser, swirl to mix, heat on a steam bath for an additional 10 min, and allow to cool to room temperature. Add through the condenser 15 mL of normal butyl alcohol that has been neutralized previously 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 normal butyl alcohol. Add 1 mL of phenolphthalein TS, and titrate with Titrant to a faint pink endpoint. Calculate the hydroxyl value in the portion of Oil taken:
Result = {[VB + (W × VA/WA) VT] × Mr × N}/W
VB== volume of Titrant consumed by the Blank (mL)
W== sample weight from the hydroxyl value determination (g)
VA== volume of Titrant consumed by the Sample in the free acid determination (mL)
WA== sample weight from the free acid determination (g)
VT== volume of Titrant consumed by the Sample in the hydroxyl value determination (mL)
Mr== milliequivalent weight of potassium hydroxide, 56.11 mg/mEq
N== actual normality of the Titrant
Acceptance criteria:  160–168
ADDITIONAL REQUIREMENTS
•  Packaging and Storage: Preserve in tight containers, and avoid exposure to excessive heat.
Auxiliary Information— Please check for your question in the FAQs before contacting USP.
Topic/Question Contact Expert Committee
Monograph Robert H. Lafaver, M.S.
Scientific Liaison
1-301-816-8335
(EXC2010) Monographs - Excipients
USP35–NF30 Page 2522