STM D6174 Inorganic Sulfate in Surfactants by Potentiometric Lead Titration

Scope: 

The ASTM D6174 test method explains how to determine the inorganic sulfate content of surfactants using a potentiometric titration process. It’s for analyzing α-olefin sulfonates, alkane sulfonates, alcohol sulfate, alcohol ether sulfate, alkylbenzene sulfonates, and other similar compounds. Anionic surfactants, including some mentioned, are widely employed in detergent compositions, and their suitability for use is determined by their purity. 

Test procedure:

A surfactant sample containing inorganic sulfate is titrated in an ethanolic medium with a standard lead solution in accordance with ASTM D6174. During the titration, a precipitate of lead sulfate is generated. The presence of ethanol and sodium perchlorate reduces the solubility of lead sulfate, intensifying the endpoint. To eliminate the possibility of carbonate interference,  acetic acid is used. An increase in lead ion activity, as measured by a lead-selective electrode,  signals the endpoint. 

Video 01: Automatic potentiometric titrator

Specimen size:

A surfactant sample containing inorganic sulfate is used as a test specimen for the ASTM  D6174. 

Data:

V = mL lead titrant ; 

M = molarity of lead titrant; 

F = factor; 

G = weight in grams of surfactant sample taken for analysis; 

D = dilution factor

Conclusion:

The ASTM D6174 test method explains how to determine the inorganic sulfate content of surfactants using a potentiometric titration process.