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 Glycol Monomethyl Ethers— 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 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 25.0 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 80; 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 Glycol Monomethyl Ethers 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 for 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 Monomethyl Ether 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 MPEG 350— Into a 5000-mL 4-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 3000 g of Polyethylene Glycol Monomethyl Ether 350. 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, sparge with nitrogen, allowing the pressure to rise to 10 mm of mercury. Heat the flask to 130 while increasing the pressure to about 60 mm of mercury. Continue stripping for 4 hours; 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 MPEG 350 to 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 MPEG 350 in 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 5 mL of the liquid ethylene oxide to a 100-mL beaker 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 MPEG 350, prepare 4 solutions, covering the range from 5 to 20 ppm for the 2 components added to the matrix (e.g., 5, 10, 15, and 20 ppm). Transfer 1.0 mL of each of these solutions to separate 22-mL pressure 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 ± 0.01 g of Polyethylene Glycol Monomethyl Ether to a 22-mL pressure headspace vial, and seal, cap, and crimp as directed for the Standard preparations.

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 50-m × 0.32-mm 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 transfer line at 140 and the detector at 250. The carrier gas is helium, flowing at a rate of about 0.8 mL per minute. On the two Calibration plots, no point digresses from its line by more than 10%.

Calibration— Place the vials containing the Standard preparations in the automated sampler, and start the sequence so that each vial is heated at a temperature of 110 for 30 minutes before a suitable portion of its headspace is injected into the chromatograph. Set the automatic sampler for a needle withdrawal time of 0.3 minute, a pressurization time of 1 minute, an injection time of 0.08 minute, and a vial pressure of 22 psig with the vial vent off. Obtain the peak areas for ethylene oxide and 1,4-dioxane, which have relative retention times of about 1.0 and 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 preparation in 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 Calibration plots. Not more than 10 ppm of ethylene oxide or 1,4-dioxane is found.

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

Test preparation— Transfer about 4 g of Polyethylene Glycol Monomethyl Ether, accurately weighed, to a 10-mL volumetric flask, dissolve in water, 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 × 1.0-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 20 mL per minute.

Procedure— Inject 1.0 µL of the Standard preparation into a suitable gas 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) small peaks that have relative retention times of about 1.0 and 3.9, and record the values as P1 and P2, respectively. Inject 1.0 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 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 Monomethyl Ether taken. Calculate the percentage of diethylene 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 combined 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 Monomethyl Ether 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.

Stripped MPEG 350 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 MPEG 350 in 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 MPEG 350, prepare 4 solutions, covering the range from 5 to 20 ppm (e.g., 5, 10, 15, and 20 ppm). Transfer 1.0 mL of each of these solutions to separate 22-mL pressure 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 621)—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 G16 in a 1-µm film thickness. The column temperature is held at 50 for 2 minutes, and then is programmed from 70 to 250 at 10 per minute, with the transfer line at 140 and the detector at 275. The carrier gas is helium, flowing at a rate of about 15 mL per minute. On the two Calibration plots, no point digresses from its line by more than 10%.

Calibration— Place the vials containing the Standard preparations in the automated sampler, and start the sequence so that each vial is heated at a temperature of 100 for 20 minutes before a suitable portion of its headspace is injected into the chromatograph. Set the automatic sampler for a needle withdrawal time of 0.3 minute, a pressurization time of 1 minute, an injection time of 0.08 minute, and a vial pressure of 22 psig 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 preparation in the automatic sampler, and chromatograph its headspace as done for the Standard preparations. Obtain the peak area and read the concentration directly from the Calibration plot. Not more than 10 ppm of 2-methoxyethanol is found.