CERTIFICATION OF SULFUR IN SRM-2724 DIESEL FUEL-OIL BY ISOTOPE-DILUTION THERMAL IONIZATION MASS-SPECTROMETRY AND X-RAY-FLUORESCENCE

SRM 2724 is a no. 2-D diesel fuel oil that has been certified for tota l sulfur concentration at 425 +/- 4 mug g-1 (95% confidence interval) by isotope dilution thermal ionization mass spectrometry, which is the most accurate and precise method for the determination of sulfur in m any different matrices. The sulfur concentration in this standard has also been measured by X-ray fluorescence (XRF) using a procedure deriv ed from ASTM method D 2622-87. The mean of the XRF measurements was 42 3 +/- 2 (1s), which demonstrates that XRF is capable of measuring sulf ur accurately and precisely at the 500 mug g-1 level when it is proper ly calibrated using accurately certified standards of a similar matrix . SRM 2724 will be useful in validating the measurement process for th e determination of sulfur by XRF in on-road diesel fuel at the 500 mug g-1 limit as mandated by EPA, effective from October 1993.