ASTM D6334 Test Method for Sulfur in Gasoline by Wavelength Dispersive X-Ray Fluorescence
3. Summary of Test Method
3.1 The sample is placed in the X-ray beam, and the intensity of the sulfur Ka line at 5.373 Å is measured. The intensity of a corrected background, measured at a recommended wavelength of 5.190 Å, or if a rhodium tube is used, 5.437 Å is subtracted from this intensity. The resultant net counting rate is then compared to a previously prepared calibration curve or equation to obtain the concentration of sulfur in mg/kg.

NOTE 2 - Caution: Exposure to excessive quantities of X radiation is injurious to health. Therefore, it is imperative that the operator avoid exposing any part of his or her person, not only to primary X-rays, but also to secondary or scattered radiation that might be present. The X-ray spectrometer should be operated in accordance with the regulations of recommendations governing the use of ionizing radiation.

4. Significance and Use
4.1 Knowledge of the presence of sulfur in petroleum products, especially fuels, helps predict performance characteristics, potential corrosion problems, and vehicle emission levels. In addition, some regulatory agencies mandate reduced levels of sulfur in reformulated type gasolines.

5. Interferences
5.1 Fuels with compositions that vary from those specified in 9.1 may be analyzed with standards made from base materials that are of similar composition to minimize matrix effects.
5.1.1 Fuels containing oxygenates may be analyzed using standards prepared with similar amounts of the same oxygenate added to the standard dilution matrix. However, round robin studies done by the Western States Petroleum Association have shown no significant bias in determining sulfur in gasolines with and without oxygenates at regulatory levels (0 to 2.7 weight percent oxygen).

5.1.2 Methanol fuels (M85 and M100) exhibit interferences at this level of detection (<100 mg/kg). They can be analyzed using a calibration curve produced by diluting the standards in a similar matrix of M85 or M100 or by Test Method D2622.