EXPLANATION
This test method uses an energy dispersive X-ray fluorescence (EDXRF) technique for the determination of total sulfur in automotive fuels with a concentration range of 6 to 50 mg/kg. The pooled limit of quantitation is 6 mg/kg sulfur. A typical analysis time is 200 to 300 sec per sample.
TEST SUMMARY
The sample is placed in the polarized X-ray beam, and the peak area of the sulfur k line at 2.307 keV is measured. The background spectrum, measured with a sulfur free white oil or other matrix matching blank sample is adapted to the measurement spectrum using adjustment regions following the instrument manufacturers' instructions, and then subtracted from the measured spectrum. 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.
INTERFERENCES - The sample and standard matrix must be well matched. Matrix mismatch can be caused by C/H ratio differences between samples and standards or by the presence of other heteroatoms.
TEST PRECISION
Where X is the average of two results in mg/kg.
Based on the analysis of a certified fuel reference sample, the method showed no apparent bias.