Ethylene Glycol, Diethylene Glycol, and Triethylene Glycol in Ethoxylated Substances

This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition

Issued and maintained by the United States Pharmacopeial Convention (USP)

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The following procedure is used to determine the concentration of residual ethylene glycol, diethylene glycol, and triethylene glycol in ethoxylated products. Ethoxylated products may contain residual ethylene glycol, diethylene glycol, and triethylene glycol as a result of the manufacturing process. The procedure is suitable for the following substances:

1. Polyethylene glycol 200

2. Polyethylene glycol 300

3. Polyethylene glycol 400

4. Polyethylene glycol 600

5. Polyethylene glycol 1000

6. Polysorbate 20

7. Polysorbate 40

8. Polysorbate 60

9. Polysorbate 80

10. Polyethylene glycol monomethyl ether 350

11. Polyethylene glycol monomethyl ether 550

12. Polyoxyl 35 castor oil

13. Polyoxyl 15 hydroxystearate

14. Polyoxyl 20 cetostearyl ether

15. Polyoxyl 8 stearate

16. Octoxynol 9

17. Nonoxynol 9

1 IMPURITIES

Procedure

Difluent: Acetone

Standard solution: 25 µg/mL of USP Ethylene Glycol RS, 40 µg/mL of USP Diethylene Glycol RS, 40 µg/mL of USP Triethylene Glycol RS, and 40 µg/mL of USP Butane-1,3-diol RS (internal standard) in Diluent

Sample solution: 40 mg/mL of the test substance and 40 µg/mL of USP Butane-1,3-diol RS (internal standard) in Diluent

1.1 Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: GC

Detector: Flame ionization

Column: 0.53-mm × 30-m capillary column bonded with a 1.0-µm layer of phase G3

Temperatures

Detector: 290°

Injection port: 270°

Column: See Table 1.

Table 1

^a Hold time was 0 min for the Standard solution and 60 min for the Sample solution and Diluent. 

Carrier gas: Helium 

Flow rate: 5.0 mL/min 

Injection volume: 1.0 µL 

Injection type: Split injection, split ratio is 2:1 

Liner: General-purpose split/splitless, tapered, glass wool, deactivated 

Run time: 26 min for the Standard solution; 86 min for the Sample solution and Diluent 

1.2 System suitability 

Sample: Standard solution 

[Note—See Table 2 for the relative retention times.] 

Table 2 

System suitability requirements

Resolution: NLT 20 between ethylene glycol and butane-1,3-diol; NLT 20 between butane-1,3-diol and diethylene glycol; NLT 20 between diethylene glycol and triethylene glycol

Tailing factor: 0.8–1.8 for each of the four peaks assigned to ethylene glycol, butane-1,3-diol, diethylene glycol, and triethylene glycol Relative standard deviation: NMT 5.0% for the peak response ratio of the respective glycol (ethylene glycol, diethylene glycol, or triethylene glycol) to the internal standard

1.3 Analysis

Samples: Standard solution and Sample solution

Identify the ethylene glycol, diethylene glycol, and triethylene glycol peaks in the Sample solution by comparison with those in the Standard solution.

Calculate the content of ethylene glycol, diethylene glycol, or triethylene glycol, in µg/g, in the portion of test substance taken:

Result = (R_U /R_S ) × (C /C_U ) × F

R_U = peak response ratio of the respective glycol to the internal standard (peak response of the respective glycol/peak response of

the internal standard) from the Sample solution

R_S = peak response ratio of the respective glycol to the internal standard (peak response of the respective glycol/peak response of the internal standard) from the Standard solution

C_S = concentration of the respective glycol (ethylene glycol, diethylene glycol, or triethylene glycol) in the Standard solution (µg/mL) 

C_U = concentration of the test substance in the Sample solution (mg/mL)

F = conversion factor (1000 mg/g)

2 ADDITIONAL REQUIREMENTS

USP Reference Standards 〈11〉

USP Butane-1,3-diol RS

USP Diethylene Glycol RS

USP Ethylene Glycol RS

USP Triethylene Glycol RS