A: Infrared Absorption á197Fñ.

B: Ultraviolet Absorption á197Uñ—

Solution: 20µg per mL.

Medium: methanol.

Standard preparation— Prepare a solution in chloroform having known concentrations of about 0.1mg of USP Clofibrate RSand 0.03mg of p-chlorophenol per mL.To 10.0mLof this solution add 5.0µLof tributyrin,and mix.

Test preparation— To 10.0mLof Clofibrate add 5.0µLof tributyrin,and mix.

Chromatographic system (see Chromatography á621ñ)—The gas chromatograph is equipped with a split injector with a 20:1split ratio,a flame-ionization detector,and a 0.53-mm ×15-m column to the internal walls of which is bonded a 1.5-µm film of phase G1.The chromatograph is programmed to maintain the column temperature at 120for 1minute,then to increase the temperature at a rate of 5per minute for 12minutes,and finally to maintain a temperature of 180for 9minutes.Maintain the injection port at 210and the detector block at 220.Helium is used as the carrier gas flowing at a rate of about 2mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed under Procedure:the relative retention times are about 0.2for p-chlorophenol,0.55for clofibrate,and 1.0for tributyrin.

Procedure— [NOTE—Use peak areas where peak responses are indicated.]Separately inject equal volumes (about 1µL)of the Standard preparationand the Test preparationinto the chromatograph,record the chromatograms,and measure the peak responses.Calculate the percentage of each impurity,other than p-chlorophenol,in the Clofibrate taken by the formula: in which Cis the concentration,in mg per mL,of USP Clofibrate RSin the Standard preparation,RUis the ratio of the response of each individual impurity peak (other than the p-chlorophenol peak)to that of the tributyrin peak obtained from the Test preparation,and RSis the ratio of the response of the clofibrate peak to that of the tributyrin peak obtained from the Standard preparation:the percentage of any impurity,other than p-chlorophenol,does not exceed 0.01%,and the total percentage of all such impurities does not exceed 0.12%.

0.1C(RU/RS),

Solvent: dimethyl sulfoxide.

Ion-exchange resin— To a beaker containing 75mLof 1Nsodium hydroxide add about 3g of a 50-to 100-mesh strongly basic styrene-divinylbenzene anion-exchange resin,and allow the mixture to stand for about 15minutes,with occasional stirring.Wash the resin with water until the last washing is neutral to litmus paper,then wash with three 50-mLportions of methanol.

Ion-exchange column— Place a plug of glass wool in the base of a 1-×15-cm ion-exchange tube,and transfer to the tube a sufficient amount of Ion-exchange resin,slurried in methanol,to produce a column bed height of from 6cm to 8cm.

Standard preparation— Dissolve an accurately weighed quantity of USP Clofibrate RSin methanol,and dilute quantitatively and stepwise with methanol to obtain a solution having a known concentration of about 20µg per mL.

Assay preparation— Transfer about 200mg of Clofibrate,accurately weighed,to a 100-mLvolumetric flask,add methanol to volume,and mix.Transfer 10.0mLof this solution to the Ion-exchange column,and collect the eluate in a 100-mLvolumetric flask.Rinse the column with 25mLof methanol,collect the rinsing in the volumetric flask,dilute with methanol to volume,and mix.Transfer 5.0mLof this solution to a 50-mLvolumetric flask,dilute with methanol to volume,and mix.

Procedure— Concomitantly determine the absorbances of the Standard preparationand the Assay preparationin 1-cm cells at the wavelength of maximum absorbance at about 226nm,with a suitable spectrophotometer,using methanol as the blank.Calculate the quantity,in mg,of C12H15ClO3in the portion of Clofibrate taken by the formula: in which Cis the concentration,in µg per mL,of USP Clofibrate RSin the Standard preparation,and AUand ASare the absorbances of the Assay preparationand the Standard preparation,respectively.