Phthalic anhydride solution— Place 49.0g of phthalic anhydride into an amber bottle,and dissolve in 300mLof pyridine from a freshly opened bottle or that has been freshly distilled over phthalic anhydride.Shake vigorously until completely dissolved.Add 7g of imidazole,swirl carefully to dissolve,and allow to stand for 16hours before using.

Test preparation for liquid Polyethylene Glycol Monomethyl Ethers— Carefully introduce 25.0mLof the Phthalic anhydride solutioninto a dry,heat-resistant pressure bottle.Add an accurately weighed amount of the specimen,equivalent to its expected average molecular weight divided by 80.Insert the stopper in the bottle,and wrap it securely in a cloth bag.

Test preparation for solid Polyethylene Glycol Monomethyl Ethers— Carefully introduce 25.0mLof Phthalic anhydride solutioninto a dry,heat-resistant pressure bottle.Add an accurately weighed amount of the specimen,equivalent to its expected molecular weight divided by 80;however,because of limited solubility,do not use more than 25g.Add 25mLof pyridine,from a freshly opened bottle or that has been freshly distilled over phthalic anhydride,swirl to dissolve,insert the stopper in the bottle,and wrap it securely in a cloth bag.

Procedure— Immerse the bottle in a water bath maintained at a temperature between 96and 100,to the same depth as that of the mixture in the bottle.Remove the bottles from the bath after 5minutes,and,without unwrapping,swirl for 30seconds to homogenize.Heat in the water bath for 30minutes (60minutes for Polyethylene Glycol Monomethyl Ethers having molecular weights of 3000or higher),then remove from the bath,and allow it to cool to room temperature.Uncap the bottle carefully to release any pressure,remove from the bag,add 10mLof water,and swirl thoroughly.Wait for 2minutes,add 0.5mLof a solution of phenolphthalein in pyridine (1in 100),and titrate with 0.5Nsodium hydroxide VSto the first pink color that persists for 15seconds,recording the volume,in mL,of 0.5Nsodium hydroxide required as S.Perform a blank determination on 25.0mLof Phthalic anhydride solutionplus any additional pyridine added to the bottle,and record the volume,in mL,of 0.5Nsodium hydroxide required as B.Calculate the average molecular weight by the formula: in which Wis the weight,in g,of the Polyethylene Glycol Monomethyl Ether taken for the Test preparation;(B-S)is the difference between the volumes of 0.5Nsodium hydroxide consumed by the blank and by the specimen;and Nis the normality of the sodium hydroxide solution.

Stripped MPEG350— Into a 5000-mL4-neck,round-bottom flask,equipped with a stirrer,a thermometer,a gas dispersion tube,a dry ice trap,a vacuum outlet,and a heating mantle,place 3000g of Polyethylene Glycol Monomethyl Ether 350.At room temperature,evacuate the flask carefully to a pressure of less than 1mm of mercury,applying the vacuum slowly while observing for excessive foaming due to entrapped gases.After any foaming has subsided,sparge with nitrogen,allowing the pressure to rise to 10mm of mercury.Heat the flask to 130while increasing the pressure to about 60mm of mercury.Continue stripping for 4hours;then cool to room temperature.Shut off the vacuum pump,and bring the flask pressure back to atmospheric pressure while maintaining nitrogen sparging.Remove the sparging tube with the gas still flowing,then turn off the gas flow.Transfer the Stripped MPEG350to a suitable nitrogen-filled container.

Standard preparations— [Caution—Ethylene oxide and 1,4-dioxane are toxic and flammable.Prepare these solutions in a well-ventilated fume hood. ]To a known weight of Stripped MPEG350in a vial that can be sealed,add a suitable quantity of 1,4-dioxane.Determine the amount added by weight difference.Using the special handling described in the following,complete the preparation.Ethylene oxide is a gas at room temperature.It is usually stored in a lecture-type gas cylinder or small metal pressure bomb.Chill the cylinder in a refrigerator before use.Transfer about 5mLof the liquid ethylene oxide to a 100-mLbeaker chilled in wet ice.Using a gas-tight gas chromatographic syringe that has been chilled in a refrigerator,transfer a suitable amount of the liquid ethylene oxide into the mixture.Immediately seal the vial,and shake.Determine the amount added by weight difference.By appropriate dilution with Stripped MPEG350,prepare 4solutions,covering the range from 5to 20ppm for the 2components added to the matrix (e.g.,5,10,15,and 20ppm).Transfer 1.0mLof each of these solutions to separate 22-mLpressure headspace vials,seal each with a silicone septum,star spring,and pressure relief safety aluminum sealing cap,and crimp the cap closed with a cap-sealing tool.

Test preparation— Transfer 1±0.01g of Polyethylene Glycol Monomethyl Ether to a 22-mLpressure headspace vial,and seal,cap,and crimp as directed for the Standard preparations.

Chromatographic system (see Chromatography á621ñ)—The gas chromatograph is equipped with a balanced pressure automatic headspace sampler and a flame-ionization detector and contains a 50-m ×0.32-mm fused silica capillary column containing bonded phase G27in a 5-µm film thickness.The column temperature is programmed from 70to 250at 10per minute,with the transfer line at 140and the detector at 250.The carrier gas is helium,flowing at a rate of about 0.8mLper minute.On the two Calibrationplots,no point digresses from its line by more than 10%.

Calibration— Place the vials containing the Standard preparationsin the automated sampler,and start the sequence so that each vial is heated at a temperature of 110for 30minutes before a suitable portion of its headspace is injected into the chromatograph.Set the automatic sampler for a needle withdrawal time of 0.3minute,a pressurization time of 1minute,an injection time of 0.08minute,and a vial pressure of 22psig with the vial vent off.Obtain the peak areas for ethylene oxide and 1,4-dioxane,which have relative retention times of about 1.0and 3.1,respectively.Plot the area versus parts per million on linear graph paper,and draw the best straight line through the points.

Procedure— Place the vial containing the Test preparationin the automatic sampler,and chromatograph its headspace as done for the Standard preparations.Obtain the peak areas of each of the components and read the concentrations directly from the Calibrationplots.Not more than 10ppm of ethylene oxide or 1,4-dioxane is found.

Standard preparation— Prepare an aqueous solution containing 500µg of ethylene glycol and 500µg of diethylene glycol in each mL.

Test preparation— Transfer about 4g of Polyethylene Glycol Monomethyl Ether,accurately weighed,to a 10-mLvolumetric flask,dissolve in water,dilute with water to volume,and mix.

Chromatographic system (see Chromatography á621ñ)—The gas chromatograph is equipped with a flame-ionization detector and a 3-mm ×1.0-m column packed with 60-to 80-mesh support S2.The column is maintained at about 200,the injection port is maintained at about 260,and nitrogen or another suitable inert gas is used as the carrier gas at a flow rate of 20mLper minute.

Procedure— Inject 1.0µLof the Standard preparationinto a suitable gas chromatograph,and record the chromatogram,adjusting the operational conditions to obtain peaks not less than 10cm in height.Measure the heights of the first (ethylene glycol)and second (diethylene glycol)small peaks that have relative retention times of about 1.0and 3.9,and record the values as P1and P2,respectively.Inject 1.0µLof the Test preparationinto the chromatograph,and record the chromatogram under the same conditions as those employed for the Standard preparation.Measure the heights of the first (ethylene glycol)and second (diethylene glycol)peaks,and record the values as p1and p2,respectively.Calculate the percentage of ethylene glycol taken by the formula: in which C1is the concentration,in µg per mL,of ethylene glycol in the Standard preparation;and Wis the weight,in mg,of Polyethylene Glycol Monomethyl Ether taken.Calculate the percentage of diethylene glycol taken by the formula: in which C2is the concentration,in µg per mL,of diethylene glycol in the Standard preparation:not more than 0.25%of combined ethylene glycol and diethylene glycol is found.

Ceric ammonium nitrate solution— Dissolve 6.25g of ceric ammonium nitrate in 100mLof 0.25Nnitric acid.Use within 3days.

Standard preparation— Transfer 62.5mg of diethylene glycol to a 25-mLvolumetric flask,dissolve in a mixture of equal volumes of freshly distilled acetonitrile and water,dilute with the same mixture to volume,and mix.

Test preparation— Dissolve 50.0g of Polyethylene Glycol Monomethyl Ether in 75mLof diphenyl ether,previously warmed,if necessary,just to melt the crystals,in a 250-mLdistilling flask.Slowly distill at a pressure of 1mm to 2mm of mercury,into a receiver graduated to 100mLin 1-mLsubdivisions,until 25mLof distillate has been collected.Add 20.0mLof water to the distillate,shake vigorously,and allow the layers to separate.Cool in an ice bath to solidify the diphenyl ether and facilitate its removal.Filter the separated aqueous layer,wash the diphenyl ether with 5.0mLof ice-cold water,pass the washings through the filter,and collect the filtrate and washings in a 25-mLvolumetric flask.Warm to room temperature,dilute with water to volume,if necessary,and mix.Mix this solution with 25.0mLof freshly distilled acetonitrile in a glass-stoppered,125-mLconical flask.

Procedure— Transfer 10.0mLeach of the Standard preparationand the Test preparationto separate 50-mLflasks,each containing 15.0mLof Ceric ammonium nitrate solution,and mix.Within 2to 5minutes,concomitantly determine the absorbances of the solutions in 1-cm cells at the wavelength of maximum absorbance at about 450nm,with a suitable spectrophotometer,using a blank consisting of a mixture of 15.0mLof Ceric ammonium nitrate solutionand 10.0mLof a mixture of equal volumes of freshly distilled acetonitrile and water:the absorbance of the solution from the Test preparationdoes not exceed that of the solution from the Standard preparation,corresponding to not more than 0.25%of combined ethylene glycol and diethylene glycol.

Stripped MPEG350 and Test preparation—Prepare as directed in the test for Free ethylene oxide and 1,4-dioxane.

Standard preparations— [Caution—2-Methoxyethanol is toxic and flammable.Prepare these solutions in a well-ventilated fume hood. ]To a known weight of Stripped MPEG350in a vial that can be sealed,add a suitable quantity of 2-methoxyethanol.Determine the amount added by weight difference.By appropriate dilution with Stripped MPEG350,prepare 4solutions,covering the range from 5to 20ppm (e.g.,5,10,15,and 20ppm).Transfer 1.0mLof each of these solutions to separate 22-mLpressure headspace vials,seal each with a silicone septum,star spring,and pressure relief safety aluminum sealing cap,and crimp the cap closed with a cap-sealing tool.

Chromatographic system (see Chromatography á621ñ)—The gas chromatograph is equipped with a balanced pressure automatic headspace sampler and a flame-ionization detector and contains a 15-m ×0.53-mm fused silica capillary column containing bonded phase G16in a 1-µm film thickness.The column temperature is held at 50for 2minutes,and then is programmed from 70to 250at 10per minute,with the transfer line at 140and the detector at 275.The carrier gas is helium,flowing at a rate of about 15mLper minute.On the two Calibrationplots,no point digresses from its line by more than 10%.

Calibration— Place the vials containing the Standard preparationsin the automated sampler,and start the sequence so that each vial is heated at a temperature of 100for 20minutes before a suitable portion of its headspace is injected into the chromatograph.Set the automatic sampler for a needle withdrawal time of 0.3minute,a pressurization time of 1minute,an injection time of 0.08minute,and a vial pressure of 22psig with the vial vent off.Obtain the peak area for 2-methoxyethanol.Plot the area versus parts per million on linear graph paper,and draw the best straight line through the points.

Procedure— Place the vial containing the Test preparationin the automatic sampler,and chromatograph its headspace as done for the Standard preparations.Obtain the peak area and read the concentration directly from the Calibrationplot.Not more than 10ppm of 2-methoxyethanol is found.