(Equivalent Test Methods: IP 107 and AFNOR M07-031)
EXPLANATION
This test method is valid in the concentration range of 0.01 to 0.04 mass % of sulfur in liquid petroleum products. By using a special sulfate analysis procedure the determination can be extended to as low as 5 mg/kg of sulfur. The direct burning procedure is applicable to gasoline, kerosene, naptha, and other liquids that can be burned completely in a wick lamp. The blending procedure is applicable to gas oils, distillate fuel oils, napthenic acids, alkyl phenols, high sulfur content petroleum products, and other materials that cannot be burned satisfactorily by the direct burning procedure.
Phosphorus compounds normally present in commercial gasoline do not interfere. A correction is needed for the small amount of acid resulting from the combustion of lead antiknock fluids in gasolines. Appreciable concentrations of acid- or base-forming elements from other sources interfere when the titration procedure is employed, since no correction is provided in these cases.
TEST SUMMARY
A sample is burned in a closed system using a suitable lamp and an artificial atmosphere composed of 70 % carbon dioxide and 30 % oxygen to prevent formation of nitrogen oxides. The oxides of sulfur produced are absorbed and oxidized to sulfuric acid by means of hydrogen peroxide solution which is then flushed with air to remove dissolved carbon dioxide. Sulfur as sulfate in the absorbent is determined acidimetrically by titration with standard NaOH solution, or gravimetrically by precipitation as barium sulfate.
Alternatively, the sample may be burned in air and the sulfur as sulfate in the absorbent be determined by precipitating as barium sulfate for weighing. For sulfur content below 0.01 mass %, it is necessary to determine sulfur in the absorber solution turbidimetrically as barium sulfate.
TEST PRECISION
Where X is the mean sulfur concentration in mass % for Test Method ASTM D1266 and in mg/kg for Test Method ASTM D1266, Annexe Al.
The bias of these test methods has not been determined.