D2959-95 – Standard Test Method Technical Guide

📐 Scope and Principle of the Test Method

This standard, ASTM D2959-95, covers the determination of ethylene oxide (EO) in polyethoxylated nonionic surfactants. Its applicability extends to any compounds that form unstable 1,2-diiodides, including propylene oxide derivatives, glycols, and polyglycol ethers and esters. The core mechanism involves cleaving the polyoxyalkylene chain with hydriodic acid (HI) under a carbon dioxide blanket, forming 1,2-diiodoethane which rapidly decomposes into ethylene and free iodine. Because the stoichiometry yields exactly one mole of iodine for every mole of ethylene oxide, a direct titration with standard sodium thiosulfate provides a precise measurement of the EO content.

Results are reported strictly as the percent of ethylene oxide by weight in the sample. It is essential that the analyst be aware that compounds where the oxyalkylene group is connected to a nitrogen atom cannot be entirely decomposed by this reaction path, which can limit the test’s applicability for certain nitrogen-based surfactants (See Note 1).