Method of Analysis for Polyethylene Glycol

1. Description

Solid grades occur as practically odorless and tasteless white, waxy, plastic material having a consistency similar to beeswax, or as creamy white flakes, beads or powders.

2. Solubility

Solid grades are freely soluble in water, soluble in acetone, in alcohol, in chloroform, in ethylene glycol monoethyl ether, in ethyl acetate and in toluene; all are insoluble in ether and in hexane.

3. Completeness & Color of Solution

Solution of 5 g of Polyethylene Glycol in 50 ml of water is colorless. It is not more than slightly hazy for solid grades.

4. Viscosity

Limit: Between 76.0 – 110.0 Centistokes.
Procedure: Determine its viscosity, using a capillary viscometer giving a flow time of not less than 200 seconds, and a liquid bath maintained at 98.9±0.3°C (210°F).

5. Average molecular weight

Limit: Not less than 90.0 % and not more than 110.0 % of the labeled nominal value. (Between 3015 to 3685).
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 standing for 16 hours before using.
Test preparation: 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 60 minutes 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:
= [2000W]/[(B – S)(N)]
Where,
W is the weight, in g, of the Polyethylene Glycol 600 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.
N is the normality of the sodium hydroxide solution.

6. pH

Limit: Between 4.5 and 7.5
Procedure: Determined potentiometrically, in a solution prepared by dissolving 5.0 g of Polyethylene Glycol 6000 in 100 ml of carbon dioxide-free water and adding 0.30 ml of saturated potassium chloride solution.

7. Residue on ignition

Limit: Not more than 0.1%
Procedure: Weigh a platinum crucible or silica crucible, previously heated at about 800°C and cooled in a desiccator (W1). Weigh accurately about 25.0 gm of the sample in the crucible and record the weight of the sample and crucible (W2). Ignite on a flame until the substance is thoroughly charred, cool the crucible and moisten the residue with 2 ml of sulphuric acid. Heat the crucible gently over a flame until the white fumes are been disappeared. Cool the crucible in a desiccator. Weigh the crucible (W3). Repeat the procedure until two successive weights do not differ by more than 0.5mg of the residue (W4).
Calculation
                                               (W4 - W1)
Residue on Ignition (%) = -------------------X 100
                                               (W2 - W1)

8. Heavy metals

Limit: Not more than 5 ppm
Sample Solution: Mix 4.0 g with 5.0 ml of 0.1N hydrochloric acid, and dilute with water to 25 ml. Transfer to Nessler cylinder. Adjust with 1N acetic acid or 6N Ammonium hydroxide to a pH between 3.0 and 4.0, using short-range indicator paper as an external indicator, dilute with water to 40 ml and mix.
Standard Preparation: Into a 50 ml Nessler cylinder, take 2 ml of Standard Lead solution (10 ppm) and dilute to 25 ml with water. Adjust with 1N acetic acid or 6N Ammonium hydroxide to a pH between 3.0 and 4.0, using short-range indicator paper as an external indicator, dilute with water to 40 ml and mix.
Monitor Solution: In a Nessler cylinder, take 25 ml of a solution prepared as directed for Sample solution and 2.0 ml of Standard solution. Adjust with 1N acetic acid or 6N Ammonium hydroxide to a pH between 3.0 and 4.0, using short-range indicator paper as an external indicator, dilute with water to 40 ml and mix.
Procedure: To each cylinder containing the standard preparation, Monitor solution and test preparation, add 2 ml of pH 3.5 Acetate Buffer, then add 1.2 ml of Thioacetamide-glycerin base TS, dilute with water to 50 ml, mix, allow standing for 2 minutes, and view downward over a white surface. The color of the solution from the sample preparation is not darker than that of the solution from standard solution and the intensity of the color of the Monitor preparation is equal to or greater than that of the standard preparation.

9. Limit of free ethylene oxide and 1,4-dioxane

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 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 5ml 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 2ml of this solution to a 5-mL beaker. Transfer 1.0ml of this solution to a 100-mL volumetric flask, dilute with Stripped polyethylene glycol 400 to volume and mix. Transfer 10ml 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 1.0ml 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. Pipette 50µL of acetaldehyde into the vial. Using the special handling described under Standard preparation, transfer about 50.0µL 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: 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 2.9ml per minute. Chromatograph the Resolution solution, and record the peak responses as directed for the 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 1.0ml 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.

10. Organic volatile impurities

Limit: Meets the requirements.
Standard Solution: Prepare a solution, in organic-free water or the solvent specified in the monograph, containing, in each ml, 12.0 µg of methylene chloride, 7.6µg of 1,4-dioxane, 1.6 µg of trichloroethylene, and 1.2µg of chloroform.[Note: Prepare fresh daily.] Pipette 5ml of the solution into a vial fitted with a septum and crimp-cap, containing 1 g of anhydrous sodium sulfate, and seal. Heat the sealed vial at 80° for 60 minutes.
Test Solution: Transfer 100 mg, accurately weighed, of the material under test to a vial, add 5.0ml of water, and 1 g of anhydrous sodium sulfate, and seal with a septum and crimp cap. Heat the sealed vial at 80° for 60 minutes.
Chromatographic System: The gas chromatograph is equipped with a flame-ionization detector, a 0.53-mm × 30-m fused-silica analytical column coated with a 3.0-µm G43 stationary phase, and a 0.53-mm × 5-m silica guard column deactivated with phenylmethyl siloxane. The carrier gas is helium with a linear velocity of about 35 cm per second. The injection port and detector temperatures are maintained at 140° and 260°, respectively. The column temperature is programmed according to the following steps. It is maintained at 40° for 20 minutes, then increased rapidly to 240° and maintained for 20 minutes. Inject the Standard Solution, and record the peak responses as directed for the procedure. A suitable system is one that yields chromatograms in which all of the components in the Standard Solution are resolved; the resolution, R, between any two components, is not less than 3; and the relative standard deviation of the individual peak responses from replicate injections is not more than 15%.
Procedure: Separately inject, using a heated gas-tight syringe, 1 ml of the headspace of the standard Solution and the test solution into the chromatograph, record the chromatograms, and measure the peak responses. Identify, based on retention time, any peaks present in the chromatogram of the Test Solution. The identity and peak response in the chromatogram may be established as being from any of the organic volatile impurities listed in Table 1 or from some other volatile impurity eluting with a comparable retention time by mass spectrometric relative abundance methods or by the use of a second validated column containing a different stationary phase.

Table 1

Organic Volatile Impurity       Limit (µg per g)

Chloroform                                   60

1,4-Dioxane                                380

Methylene Chloride                      600

Trichloroethylene                          80

The amount of each organic volatile impurity present in the material does not exceed the limit given in the accompanying table.