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

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

Test preparation for liquid Polyethylene Glycols— Carefully introduce 25.0 mL of the Phthalic 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 25.0 mL of Phthalic 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 25 g. Add 25 mL of 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 96 and 100, to the same depth as that of the mixture in the bottle. Remove the bottles from the bath after 5 minutes, and, without unwrapping, swirl for 30 seconds to homogenize. Heat in the water bath for 30 minutes (60 minutes for Polyethylene Glycols having molecular weights of 3000 or 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 10 mL of water, and swirl thoroughly. Wait 2 minutes, add 0.5 mL of a solution of phenolphthalein in pyridine (1 in 100), and titrate with 0.5 N sodium hydroxide VS to the first pink color that persists for 15 seconds, recording the volume, in mL, of 0.5 N sodium hydroxide required as S. Perform a blank determination on 25.0 mL of Phthalic anhydride solution plus any additional pyridine added to the bottle, and record the volume, in mL, of 0.5 N sodium hydroxide required as B. Calculate the average molecular weight by the formula: in which W is the weight, in g, of the Polyethylene Glycol taken for the Test preparation; (B – S) is the difference between the volumes of 0.5 N sodium hydroxide consumed by the blank and by the specimen, and N is the normality of the sodium hydroxide solution.

Stripped polyethylene glycol 400— Into a 5000-mL 3-neck, round-bottom flask equipped with a stirrer, a gas dispersion tube, and a vacuum outlet, place 3000 g of Polyethylene Glycol 400. At room temperature, evacuate the flask carefully to a pressure of less than 1 mm 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 10 mm 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 1 hour. [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 the Stripped polyethylene glycol 400 to 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 4.90 g of Stripped polyethylene glycol 400 to a tared 22-mL pressure headspace vial that can be sealed. Add 48 µL of 1,4-dioxane, equivalent to 50 mg 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 5 mL of the liquid ethylene oxide to a 100-mL beaker chilled in wet ice. Using a gas-tight syringe that has been chilled in a refrigerator, transfer 57 µL of the liquid ethylene oxide, equivalent to 50 mg of ethylene oxide, to the mixture contained in the headspace vial, and mix. With the aid of a syringe, transfer about 2 mL of this solution to a 5-mL beaker. Transfer 1.0 mL of this solution to a 100-mL volumetric flask, dilute with Stripped polyethylene glycol 400 to volume, and mix. Transfer 10 mL of this solution to a 100-mL volumetric flask, dilute with Stripped polyethylene glycol 400 to volume, and mix to obtain a Standard preparation having known concentrations of 10 µg per g for both ethylene oxide and 1,4-dioxane. Transfer 1.0 mL of the Standard preparation to a 22-mL pressure 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 4.90 g of Stripped polyethylene glycol 400 to a 22-mL pressure headspace vial. Pipet 50 µL of acetaldehyde into the vial. Using the special handling described under Standard preparation, transfer about 50.0 µL of liquid ethylene oxide into the vial. Immediately seal the vial, and shake. Transfer 1.0 mL of this solution to a 100-mL volumetric flask, dilute with Stripped polyethylene glycol 400 to volume, and mix. Transfer 10.0 mL of this solution to a 100-mL volumetric flask, dilute with Stripped polyethylene glycol 400 to volume, and mix. Transfer 1.0 mL of this Resolution solution to a 22-mL pressure headspace vial; and seal, cap, and crimp as directed for the Standard preparation.

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

Chromatographic system (see Chromatography 621)— 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 G27 in a 5-µm film thickness. The column temperature is programmed from 70 to 250 at 10 per minute, with the injection port at 85 and the detector at 250. The carrier gas is helium at a flow rate of about 2.9 mL per minute. Chromatograph the Resolution solution, and record the peak responses as directed for Procedure: the relative retention times are about 0.9 for acetaldehyde and 1.0 for 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 the Standard preparation and the Test preparation into the automated sampler, and heat the vials at a temperature of 80 for 30 minutes. Using a 2-mL gas syringe preheated in an oven at 90, separately inject 1.0 mL of the headspace from each vial into the chromatograph, record the chromatogram, and measure the areas for the major peaks. [note—A headspace 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 1.0 and 3.4, respectively. The peak areas for ethylene oxide and 1,4-dioxane in the chromatogram of the Test preparation are not greater than those of the corresponding peaks in the chromatogram of the Standard preparation, corresponding to not more than 10 µg per g of ethylene oxide and not more than 10 µg per g of 1,4-dioxane.

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

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

Chromatographic system (see Chromatography 621)— The gas chromatograph is equipped with a flame-ionization detector and a 3-mm × 1.5-m stainless steel column packed with 12% G13 on support S1NS. The carrier gas is nitrogen or another suitable inert gas, flowing at a rate of 50 mL per 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 2.0 µL) of the Standard preparation into the chromatograph, and record the chromatogram, adjusting the operational conditions to obtain peaks not less than 10 cm in height. Measure the heights of the first (ethylene glycol) and second (diethylene glycol) peaks, and record the values as P1 and P2, respectively. Inject a volume (about 2.0 µL) of the Test preparation into 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 p1 and p2, respectively. Calculate the percentage of ethylene glycol in the portion of Polyethylene Glycol taken by the formula: in which C1 is the concentration, in µg per mL, of ethylene glycol in the Standard preparation; and W is 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 which C2 is the concentration, in µg per mL, of diethylene glycol in the Standard preparation: not more than 0.25% of the sum of ethylene glycol and diethylene glycol is found.

Ceric ammonium nitrate solution— Dissolve 6.25 g of ceric ammonium nitrate in 100 mL of 0.25 N nitric acid. Use within 3 days.

Standard preparation— Transfer 62.5 mg of diethylene glycol to a 25-mL volumetric 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 50.0 g of Polyethylene Glycol in 75 mL of diphenyl ether, previously warmed, if necessary, just to melt the crystals, in a 250-mL distilling flask. Slowly distill at a pressure of 1 mm to 2 mm of mercury, into a receiver graduated to 100 mL in 1-mL subdivisions, until 25 mL of distillate has been collected. Add 20.0 mL of 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 5.0 mL of ice-cold water, pass the washings through the filter, and collect the filtrate and washings in a 25-mL volumetric flask. Warm to room temperature, dilute with water to volume, if necessary, and mix. Mix this solution with 25.0 mL of freshly distilled acetonitrile in a glass-stoppered, 125-mL conical flask.

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