Engine fuel. Determination of mercaptan and hydrogen sulphide sulphur content by potentiometric titration
Before starting the analysis, it is necessary to carry out a qualitative determination of hydrogen sulfide in the fuel sample under study. If there is no hydrogen sulfide, a standard titration is carried out, determining the thiol content by the consumption of silver nitrate ammoniaate (method A) or an alcohol solution of silver nitrate (method B).
If the sample contains hydrogen sulfide, then first titrate the crude sample, and then titrate the sample washed from hydrogen sulfide, calculating the content of the latter by the difference in titrant volumes spent on the first and second experiments.
If a silver sulfide electrode is used as the measuring electrode, the equivalence point is determined by the potential jump. When using an antimony electrode, if hydrogen sulfide and thiols are determined together, then the potential jump is also taken as the equivalence point. And if the titration is performed on a sample washed from hydrogen sulfide or not containing it initially, then the potential shift on the graph towards positive values means the end of titration.
The State Standard of the Union of SSR GOST 17323 provides two methods that can be used to determine the mass fraction of mercaptan and hydrogen sulfide sulfur by potentiometric titration.
Method A is intended to determine the mass fraction of mercaptan and hydrogen sulfide sulfur by potentiometric titration with silver nitrate ammoniaate in jet fuels, diesel and gasoline.
Method B is intended to determine the mass fraction of mercaptan sulfur in the range (0.0003-0.01)% by potentiometric titration with silver nitrate in jet fuel.
The determination is not influenced by such organic compounds as sulfides, disulfides and thiophene, as well as elemental sulfur in an amount of less than 0.0005% (by weight).
Method B is used when there is disagreement in the assessment of the mass fraction of mercaptan sulfur in jet fuel.