MERCAPTAN SULFUR IN PETROLEUM PRODUCTS: ASTM D3227
(Equivalent Test Methods: IP 342, ISO 3012, JIS K 2276, and AFNOR M07-022)
EXPLANATION
Mercaptan sulfur has an objectionable odor, an adverse effect on fuel system elastomers, and is corrosive to fuel system components. This test method covers the determination of mercaptan sulfur in gasolines, kerosenes, aviation turbine fuels, and distillate fuels containing from 0.0003 to 0.01 mass % of mercaptan sulfur. Organic sulfur compounds such as sulfides, disulfides, and thiophene do not interfere. Elemental sulfur in amount <0.0005 mass % does not interfere. Hydrogen sulfide will interfere if not removed by precipitating with cadmium sulfate.
TEST SUMMARY
The hydrogen sulfide-free sample is dissolved in an alcoholic sodium acetate titration solvent and titrated potentiometrically with silver nitrate solution, using as an indicator the potential between a glass reference electrode and a silver/silver-sulfide indicating electrode. Under these conditions, the mercaptan sulfur is precipitated as silver mercaptide and the end point of the titration is shown by a large change in cell potential.
TEST PRECISION
Repeatability: 0.00007 + 0.027X
Reproducibility: 0.00031 + 0.042X
Where X is the average mercaptan sulfur, mass %.
The bias of this test method has not been determined.
