Analysis of sulfur in ULSD (ultra-low sulfur diesel). Regulations around the world have limited the amount of sulfur in various fuels oils with particular attention to diesel fuel. For many years road diesel has been limited to a maximum sulfur concentration between 10-15 ppm, depending on the global region. Now these limits are expanded to all diesel fuel, including use in large engines and off-road diesel engines. The results shown here indicate the Rigaku NEX QC+ EDXRF analyzer gives excellent performance for the measurement of ULSD as per standard test method ISO 13032.