Appendix VIII K. Ethylene Glycol and Diethylene Glycol in Ethoxylated Substances

Ethoxylated substances may contain varied amounts of ethylene glycol and diethylene glycol, as a result of the manufacturing process. The following method may be used for the quantitative determination of these substances, in particular in the case of the following surfactants: macrogolglycerol ricinoleate, macrogolglycerol hydroxystearate, macrogol 15 hydroxystearate, nonoxinol 9 and macrogol cetostearyl ether.

Gas chromatography (2.2.28).

Internal standard solution Dissolve 30.0 mg of 1,2-pentanediol R in acetone R and dilute to 30.0 mL with the same solvent. Dilute 1.0 mL of this solution to 20.0 mL with acetone R.

Test solution Dissolve 0.500 g of the substance to be examined in the internal standard solution and dilute to 10.0 mL with the same solution.

Reference solution (a) Mix 30.0 mg of ethylene glycol R with acetone R and dilute to 100.0 mL with the same solvent. Dilute 1.0 mL to 10.0 mL with the internal standard solution.

Reference solution (b) Prepare a solution of diethylene glycol R with a concentration corresponding to the prescribed limit and using the same solvents as for the preparation of reference solution (a).

Column:

• — material: fused silica,

• — size: l = 30 m, Ø = 0.53 mm,

• — stationary phase: macrogol 20 000 R (film thickness 1 µm).

Carrier gas helium for chromatography R.

Flow rate 10 mL/min.

Split ratio 1:3.

Temperature:

Detection Flame ionisation.

Injection 2 µL.

Relative retention with reference to 1,2-pentanediol (retention time = about 19 min): ethylene glycol = about 0.7; diethylene glycol = about 1.3.