Scope: 

The ASTM D6173 test method is solely used for determining the active matter in the following surfactants: alcohol ether sulfate, alpha-olefin sulfonate, alkyl benzene sulfonic acid, alcohol sulfate, sodium alkylbenzene sulfonate/sodium xylene sulfonate blend (5:1), sodium alkylbenzene sulfonate/so (22:1). Titration of various ratio mixes of sodium alkylbenzene sulfonate and sodium xylene sulfonate is also described in this test technique. This test method’s most popular anionic surfactants are widely utilized in synthetic detergents and other home cleaners. 

Test procedure:

The ASTM D6173 test method describes a potentiometric titration procedure for determining the active matter in anionic surfactants. After dissolving the anionic surfactant in water, the pH of the solution is adjusted to match the kind of anionic surfactant being tested. A surfactant electrode is used to titrate an anionic surfactant with a standard solution of hyamine, and the reaction involves the creation of a complex between the anionic surfactant and the cationic titrant (hyamine), which then precipitates. The surfactant electrode appears to respond to an excess of titrant at the endpoint with a large enough potential change to produce a well-defined inflection in the titration curve. 

Video 01: Surfactant titration analysis

Specimen size:

A sample of approximately 0.016 meq/4.0 mL anionic substance is utilized for the ASTM D6173  test, which is measured to the nearest 0.1 mg. 

Data:

In ASTM D6173, the percent actives in anionic surfactants are calculated as follows: 

where: 

A = standard hyamine 1622 solution required for titration

N = normality of the standard hyamine 1622 solution 

M = molecular weight of the anionic surfactant

 D = initial dilution of the sample 

S = weight of the sample 

A= aliquot taken for titration

Conclusion:

The ASTM D6173 test method is solely used for determining the active matter in the following surfactants: alcohol ether sulfate, alpha-olefin sulfonate, alkyl benzene sulfonic acid, alcohol sulfate, sodium alkylbenzene sulfonate/sodium xylene sulfonate blend (5:1), sodium alkylbenzene sulfonate/so (22:1).