A: Infrared Absorption á197Fñ.

B: Prepare the Test solutionand the Resolution solutionas directed in the test for Limit of diethylene glycol and related compounds.Dilute a portion of each solution,stepwise if necessary,with water to obtain the Diluted test solutionand the Diluted resolution solutionhaving concentrations of about 0.1mg per mL.Proceed as directed for Procedurein the test for Limit of diethylene glycol and related compounds:the retention time of the glycerin peak in the chromatogram of the Diluted test solutioncorresponds to that obtained in the chromatogram of the Diluted resolution solution.

Resolution solution— Dissolve accurately weighed quantities of diethylene glycol and USP Glycerin RSin water,and dilute quantitatively,and stepwise if necessary,with water to obtain a solution having a known concentration of about 0.5mg of each per mL.

Standard solution— Dissolve an accurately weighed quantity of diethylene glycol in water,and dilute quantitatively,and stepwise if necessary,with water to obtain a solution having a known concentration of about 0.05mg per mL.

Test solution— Transfer 5g of Glycerin,accurately weighed,to a 100-mLvolumetric flask,dissolve in and dilute with water to volume,and mix.

Chromatographic system (see Chromatography á621ñ)—The gas chromatograph is equipped with a flame-ionization detector,a 0.53-mm ×30-m fused-silica analytical column coated with 3.0-µm G43stationary phase,and an inlet liner having an inverted cup or spiral structure.The chromatograph is programmed as follows.Initially,the column temperature is equilibrated at 100until the time of injection,is increased at a rate of 7.5per minute to 220,and is maintained at 220for 4minutes.The injection port temperature is maintained at 220,and the detector temperature is maintained at 250.The carrier gas is helium.The split flow ratio is about 10:1,and the linear flow is maintained at about 38cm per second.Chromatograph the Resolution solution,and record the peak responses as directed for Procedure:the resolution,R,between diethylene glycol and glycerin is not less than 7.0.Chromatograph the Standard solution,and record the peak responses as directed for Procedure:the relative standard deviation for replicate injections is not more than 15%.

Procedure— Separately inject equal volumes (about 0.5µL)of the Standard solutionand the Test solutioninto the chromatograph,record the chromatograms,and measure the responses for all the peaks.Calculate the percentage of diethylene glycol in the portion of Glycerin taken by the formula: in which CSis the concentration,in mg per mL,of diethylene glycol in the Standard solution;CUis the concentration,in mg per mL,of Glycerin in the Test solution;and rUand rSare the peak responses for diethylene glycol obtained from the Test solutionand the Standard solution,respectively:not more than 0.1%is found.Calculate the percentage of each other impurity,excluding any solvent peaks,in the portion of Glycerin taken by the formula: in which riis the peak response of each individual impurity obtained from the Test solution;and rsis the sum of the responses of all the peaks obtained from the Test solution:not more than 0.1%of any individual impurity,excluding diethylene glycol,is found;and not more than 1.0%of total impurities,including diethylene glycol,is found.

Sodium periodate solution— Dissolve 60g of sodium metaperiodate in sufficient water containing 120mLof 0.1Nsulfuric acid to make 1000mL.Do not heat to dissolve the periodate.If the solution is not clear,pass through a sintered-glass filter.Store the solution in a glass-stoppered,light-resistant container.Test the suitability of this solution as follows.Pipet 10mLinto a 250-mLvolumetric flask,dilute with water to volume,and mix.To about 550mg of Glycerin dissolved in 50mLof water add 50mLof the diluted periodate solution with a pipet.For a blank,pipet 50mLof the solution into a flask containing 50mLof water.Allow the solutions to stand for 30minutes,then to each add 5mLof hydrochloric acid and 10mLof potassium iodide TS,and rotate to mix.Allow to stand for 5minutes,add 100mLof water,and titrate with 0.1Nsodium thiosulfate,shaking continuously and adding 3mLof starch TSas the endpoint is approached.The ratio of the volume of 0.1Nsodium thiosulfate required for the glycerin–periodate mixture to that required for the blank should be between 0.750and 0.765.

Procedure— Transfer about 400mg of Glycerin,accurately weighed,to a 600-mLbeaker,dilute with 50mLof water,add bromothymol blue TS,and acidify with 0.2Nsulfuric acid to a definite green or greenish yellow color.Neutralize with 0.05Nsodium hydroxide to a definite blue endpoint,free from green color.Prepare a blank containing 50mLof water,and neutralize in the same manner.Pipet 50mLof the Sodium periodate solutioninto each beaker,mix by swirling gently,cover with a watch glass,and allow to stand for 30minutes at room temperature (not exceeding 35)in the dark or in subdued light.Add 10mLof a mixture of equal volumes of ethylene glycol and water,and allow to stand for 20minutes.Dilute each solution with water to about 300mL,and titrate with 0.1Nsodium hydroxide VSto a pHof 8.1±0.1for the specimen under assay and 6.5±0.1for the blank,using a pHmeter.Each mLof 0.1Nsodium hydroxide,after correction for the blank,is equivalent to 9.210mg of C3H8O3.