Nominal Average Molecular Weight	Viscosity Range,Centistokes	Nominal Average Molecular Weight	Viscosity Range,Centistokes
200	3.9to 4.8	2200	43to 56
300	5.4to 6.4	2300	46to 60
400	6.8to 8.0	2400	49to 65
500	8.3to 9.6	2500	51to 70
600	9.9to 11.3	2600	54to 74
700	11.5to 13.0	2700	57to 78
800	12.5to 14.5	2800	60to 83
900	15.0to 17.0	2900	64to 88
1000	16.0to 19.0	3000	67to 93
1100	18.0to 22.0	3250	73to 105
1200	20.0to 24.5	3350	76to 110
1300	22.0to 27.5	3500	87to 123
1400	24to 30	3750	99to 140
1450	25to 32	4000	110to 158
1500	26to 33	4250	123to 177
1600	28to 36	4500	140to 200
1700	31to 39	4750	155to 228
1800	33to 42	5000	170to 250
1900	35to 45	5500	206to 315
2000	38to 49	6000	250to 390
2100	40to 53	6500	295to 480
		7000	350to 590
		7500	405to 735
		8000	470to 900

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 Glycols— Carefully introduce 25.0mLof thePhthalic anhydride solution into a dry,heat-resistant pressure bottle.Add an accurately weighed amount of the specimen,equivalent to its expected average molecular weight divided by 160.Insert the stopper in the bottle,and wrap it securely in a cloth bag.

Test preparation for solid Polyethylene Glycols— Carefully introduce 25.0mLofPhthalic anhydride solution into a dry,heat-resistant pressure bottle.Add an accurately weighed amount of the specimen,equivalent to its expected molecular weight divided by 160;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 Glycols 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 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 asS.Perform a blank determination on 25.0mLofPhthalic anhydride solution plus any additional pyridine added to the bottle,and record the volume,in mL,of 0.5Nsodium hydroxide required asB.Calculate the average molecular weight by the formula: in which Wis the weight,in g,of the Polyethylene Glycol taken for theTest 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 polyethylene glycol 400— Into a 5000-mL3-neck,round-bottom flask equipped with a stirrer,a gas dispersion tube,and a vacuum outlet,place 3000g of Polyethylene Glycol 400.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 and while stirring continuously,sparge with nitrogen,allowing the pressure to rise to 10mm of mercury.[NOTE—The 10-mm value is a guideline.Deviations from this value only affect the total time required to strip the Polyethylene Glycol 400.]Continue stripping for a minimum of 1hour.[NOTE—Completeness of the stripping procedure should be verified by making a headspace injection of the stripped polyethylene glycol 400.]Shut off the vacuum pump,and bring the flask pressure back to atmospheric pressure while maintaining nitrogen sparging.Remove the gas dispersion tube with the gas still flowing,and then turn off the gas flow.Transfer theStripped polyethylene glycol 400to a suitable nitrogen-filled container.

Standard preparation— [Caution—Ethylene oxide and 1,4-dioxane are toxic and flammable.Prepare these solutions in a well-ventilated fume hood. ]Transfer 4.90g ofStripped polyethylene glycol 400to a tared 22-mLpressure headspace vial that can be sealed.Add 48µLof 1,4-dioxane,equivalent to 50mg of 1,4-dioxane,from a syringe,seal,and cap the vial.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 syringe that has been chilled in a refrigerator,transfer 57µLof the liquid ethylene oxide,equivalent to 50mg of ethylene oxide,to the mixture contained in the headspace vial,and mix.With the aid of a syringe,transfer about 2mLof this solution to a 5-mLbeaker.Transfer 1.0mLof this solution to a 100-mLvolumetric flask,dilute withStripped polyethylene glycol 400to volume,and mix.Transfer 10mLof this solution to a 100-mLvolumetric flask,dilute withStripped polyethylene glycol 400to volume,and mix to obtain aStandard preparation having known concentrations of 10µg per g for both ethylene oxide and 1,4-dioxane.Transfer 1.0mLof theStandard preparation to a 22-mLpressure headspace vial,seal with a silicone septum with or without a pressure relief star spring and a pressure relief safety aluminum sealing cap,and crimp the cap closed with a cap-sealing tool.

Resolution solution— Transfer 4.90g ofStripped polyethylene glycol 400to a 22-mLpressure headspace vial.Pipet 50µLof acetaldehyde into the vial.Using the special handling described underStandard preparation,transfer about 50.0µLof liquid ethylene oxide into the vial.Immediately seal the vial,and shake.Transfer 1.0mLof this solution to a 100-mLvolumetric flask,dilute with Stripped polyethylene glycol 400to volume,and mix.Transfer 10.0mLof this solution to a 100-mLvolumetric flask,dilute withStripped polyethylene glycol 400to volume,and mix.Transfer 1.0mLof thisResolution solution to a 22-mLpressure headspace vial;and seal,cap,and crimp as directed for theStandard preparation.

Test preparation— Transfer 1.0g of Polyethylene Glycol,to a 22-mLpressure headspace vial;and seal,cap,and crimp as directed for theStandard preparation.

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 0.32-mm ×50-m 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 injection port at 85and the detector at 250.The carrier gas is helium at a flow rate of about 2.9mLper minute.Chromatograph theResolution solution,and record the peak responses as directed forProcedure:the relative retention times are about 0.9for acetaldehyde and 1.0for ethylene oxide;and the resolution,R,between the acetaldehyde peak and the ethylene oxide peak is not less than 1.3.

Procedure— Place the vials containing theStandard preparation and theTest preparation into the automated sampler,and heat the vials at a temperature of 80for 30minutes.Using a 2-mLgas syringe preheated in an oven at 90,separately inject 1.0mLof the headspace from each vial into the chromatograph,record the chromatogram,and measure the areas for the major peaks.[NOTE—Aheadspace apparatus that automatically transfers the measured amount of headspace may be used to perform the injection.]The relative retention times for ethylene oxide and 1,4-dioxane are about 1.0and 3.4,respectively.The peak areas for ethylene oxide and 1,4-dioxane in the chromatogram of theTest preparation are not greater than those of the corresponding peaks in the chromatogram of theStandard preparation,corresponding to not more than 10µg per g of ethylene oxide and not more than 10µg per g of 1,4-dioxane.

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

Test preparation— Transfer about 4g of Polyethylene Glycol,accurately weighed,to a 10-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 and a 3-mm ×1.5-m stainless steel column packed with 12%G13on support S1NS.The carrier gas is nitrogen or another suitable inert gas,flowing at a rate of 50mLper minute.The column temperature is maintained at about 140,the injection port temperature is maintained at about 250,and the flame-ionization detector temperature is maintained at 280.

Procedure— Inject a volume (about 2.0µL)of theStandard preparation into the 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)peaks,and record the values asP1andP2,respectively.Inject a volume (about 2.0µL)of theTest preparation into the chromatograph,and record the chromatogram under the same conditions as those employed for theStandard preparation.Measure the heights of the first (ethylene glycol)and second (diethylene glycol)peaks,and record the values asp1andp2,respectively.Calculate the percentage of ethylene glycol in the portion of Polyethylene Glycol taken by the formula: in whichC1is the concentration,in µg per mL,of ethylene glycol in theStandard preparation;andWis the weight,in mg,of Polyethylene Glycol taken.Calculate the percentage of diethylene glycol in the portion of Polyethylene Glycol taken by the formula: in whichC2is the concentration,in µg per mL,of diethylene glycol in theStandard preparation:not more than 0.25%of the sum of 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 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 theStandard preparation and theTest preparation to 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 solution and 10.0mLof a mixture of equal volumes of freshly distilled acetonitrile and water:the absorbance of the solution from theTest preparation does not exceed that of the solution from theStandard preparation,corresponding to not more than 0.25%of combined ethylene glycol and diethylene glycol.