ASTM D 3227
Standard Test Method for (Thiol Mercaptan) Sulfur in Gasoline, Kerosine, Aviation Turbine, and Distillate Fuels (Potentiometric Method)
The essence of the method is that a sample that does not contain hydrogen sulfide is dissolved in a solvent: an alcoholic solution of sodium acetate and potentiometric titration is carried out with a solution of silver nitrate using the potential between the glass reference electrode and the indicator silver sulfide electrode. Under these conditions, mercaptan sulfur precipitates at the end of the titration as silver mercaptide, as evidenced by a significant change in the potential in the titration cell.
This method covers the determination of mercaptan sulfur in gasolines, kerosene, turbojet fuels and distillate fuels containing from 0.0003% to 0.01% mercaptan sulfur by mass.