469 ETHYLENE GLYCOL, DIETHYLENE GLYCOL, AND TRIETHYLENE GLYCOL IN ETHOXYLATED SUBSTANCES
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
IMPURITIES
•  Procedure
Diluent:  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
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
Initial
Temperature
()		 Temperature
Ramp
(/min)		 Final
Temperature
()		 Hold Time at Final
Temperature
(min)
40 10 60 5
60 10 170 0
170 15 280 0, 60a
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
System suitability 
Sample:  Standard solution
[Note—See Table 2 for the relative retention times. ]
Table 2
Name Relative
Retention
Time
Ethylene glycol 0.45
Butane-1,3-diol
(internal standard)		 1.00
Diethylene glycol 1.25
Triethylene glycol 1.70
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
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 = (RU/RS) × (CS/CU) × F

RU== 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
RS== 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
CS== concentration of the respective glycol (ethylene glycol, diethylene glycol, or triethylene glycol) in the Standard solution (µg/mL)
CU== concentration of the test substance in the Sample solution (mg/mL)
F== conversion factor (1000 mg/g)
ADDITIONAL REQUIREMENTS
•  USP Reference Standards 11
USP Butane-1,3-diol RS
USP Diethylene Glycol RS Click to View Structure
USP Ethylene Glycol RS Click to View Structure
USP Triethylene Glycol RS
Auxiliary Information— Please check for your question in the FAQs before contacting USP.
Topic/Question Contact Expert Committee
General Chapter Hong Wang, Ph.D.
Senior Scientific Liaison
(301) 816-8351		 (GCCA2010) General Chapters - Chemical Analysis
Reference Standards RS Technical Services
1-301-816-8129
rstech@usp.org
USP38–NF33 Page 324
Pharmacopeial Forum: Volume No. 39(4)