Internal standard solution— In a 100-mL volumetric flask dissolve about 1.2 g of di(2-ethylhexyl)phthalate in chloroform, dilute with chloroform to volume, and mix.

Chromatographic system (see Chromatography 621)—Under typical conditions, the instrument is equipped with a flame-ionization detector and contains a 1.8-m × 4-mm column packed with 4% liquid phase G25 on support S1, and conditioned by flushing with helium for 2 to 5 minutes, then heating without further flushing at 250 for not less than 30 minutes, then cooling to room temperature, and finally heating while helium is flowing through it at 250 for not less than 60 minutes. During the chromatographic separation, the column temperature is maintained at 245, and the injection port and detector block temperatures are maintained at about 300. The carrier gas is helium, and its flow rate is adjusted to obtain a peak due to castor oil about 5.5 minutes after introduction of the specimen and an internal standard peak about 8 minutes after introduction of the specimen.

Procedure— Transfer an accurately weighed amount of the well-shaken Emulsion, equivalent to about 100 mg of castor oil, to a long-neck, round-bottom, 100-mL boiling flask equipped with a suitable reflux condenser connected by a ground-glass joint. To a similar flask transfer about 100 mg of castor oil, accurately weighed, to provide the standard. Carry out the following steps on each: Add 30 mL of a mixture of 300 mL of methanol and 3.7 mL of sulfuric acid, reflux in a water bath maintained at 75 to 80 for 2.5 hours, cool, and rinse down the condenser with 10 mL of water. Transfer the contents of the flask to a 125-mL separator with the aid of 10 mL of water. Rinse the condenser and the flask with 25 mL of solvent hexane, and transfer to the separator. Shake the separator for 2 minutes, and draw off the aqueous layer into a second 125-mL separator. Add 20 mL of solvent hexane to the second separator, shake for 2 minutes, discard the aqueous layer, and transfer the solvent hexane layer to the first separator with the aid of 10 mL of solvent hexane. Wash the combined extracts with three 5-mL portions of water, discarding the washings, and transfer the washed extract to a 125-mL conical flask, through a funnel containing anhydrous sodium sulfate, with the aid of 25 mL of solvent hexane. Place the flask in a hot water bath, and evaporate with the aid of a current of air to dryness. To the residue add 10.0 mL of Internal standard solution, and mix until solution is complete. Inject about 5 µL into the gas chromatograph, and measure the heights of the peaks due to castor oil and internal standard. Calculate the quantity, in mg, of castor oil in the portion of Emulsion taken by the formula: in which qr is the weight, in mg, of castor oil taken for the standard; and RA and RS are the ratios of the heights of the peaks due to castor oil and internal standard obtained from the Emulsion and the standard, respectively.