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

Chromatographic system (see Chromatography á621ñ)—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 G25on support S1,and conditioned by flushing with helium for 2to 5minutes,then heating without further flushing at 250for not less than 30minutes,then cooling to room temperature,and finally heating while helium is flowing through it at 250for not less than 60minutes.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 5.5minutes after introduction of the specimen and an internal standard peak about 8minutes after introduction of the specimen.

Procedure— Transfer an accurately weighed amount of the well-shaken Emulsion,equivalent to about 100mg of castor oil,to a long-neck,round-bottom,100-mLboiling flask equipped with a suitable reflux condenser connected by a ground-glass joint.To a similar flask transfer about 100mg of castor oil,accurately weighed,to provide the standard.Carry out the following steps on each:Add 30mLof a mixture of 300mLof methanol and 3.7mLof sulfuric acid,reflux in a water bath maintained at 75to 80for 2.5hours,cool,and rinse down the condenser with 10mLof water.Transfer the contents of the flask to a 125-mLseparator with the aid of 10mLof water.Rinse the condenser and the flask with 25mLof solvent hexane,and transfer to the separator.Shake the separator for 2minutes,and draw off the aqueous layer into a second 125-mLseparator.Add 20mLof solvent hexane to the second separator,shake for 2minutes,discard the aqueous layer,and transfer the solvent hexane layer to the first separator with the aid of 10mLof solvent hexane.Wash the combined extracts with three 5-mLportions of water,discarding the washings,and transfer the washed extract to a 125-mLconical flask,through a funnel containing anhydrous sodium sulfate,with the aid of 25mLof 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 10.0mLof Internal standard solution,and mix until solution is complete.Inject about 5µLinto 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 qris the weight,in mg,of castor oil taken for the standard,and RAand RSare the ratios of the heights of the peaks due to castor oil and internal standard obtained from the Emulsion and the standard,respectively.