EXPLANATION
This test method is valid at sulfur levels of 3.0 to 100 ppm in light liquid hydrocarbons boiling in the range from 26 to 274° C. Samples with higher sulfur levels may be analyzed after proper dilutions. This test method is applicable in the presence of total halides up to 10 times the sulfur concentration, and total nitrogen concentration up to 1000 times the sulfur level. The method is not applicable in the presence of total heavy metal concentrations (for example, nickel, vanadium, lead, etc.) in excess of 500 ppm. Stringent techniques must be employed and all possible sources of sulfur contamination must be eliminated to achieve the quantitative detectability that this test method is capable of.
TEST SUMMARY
A liquid sample is injected into a combustion tube maintained at about 800° C in a flowing stream of gas mixture of 80 % oxygen and 20 % inert gas such as nitrogen or argon, etc. Oxidative pyrolysis converts the sulfur to sulfur dioxide, which then flows into a tiration cell where it reacts with triiodide ion present in the electrolyte. The triiodide thus consumed is coulometrically replaced and the total current required to replace it is a measure of the sulfur present in the injected sample.
TEST PRECISION
Where X is the average of duplicate results in mg/kg.
A pooled limit of quantitation (PLOQ) of ~3 mg/kg for gasoline samples and ~5 mg/kg for diesel sample types was obtained.