(Equivalent Test Methods: DIN 51400 T6 and JIS K 2541)
EXPLANATION
This test method is applicable for the analysis of diesel fuel, jet fuel, kerosene, other distillate oil, naptha, residual oil, lubricating base oil, hydraulic oil, crude oil, unleaded gasoline, M-85, and M-100. This test method has been tested at least in the sulfur concentration range of 3 mg/kg to 5.3 mass %. Samples with higher sulfur levels can be analyzed with proper dilution. Volatile materials, such as high vapor pressure gasolines or light hydrocarbons, may not meet the stated precision limits of this test method because of the selective loss of light materials during the analysis. When the elemental composition (excluding sulfur) of samples differs significantly from the standards, errors in the analysis can occur. To maintain the same carbon-to-hydrogen ratio, the standard and the sample matrix must be well matched for this analysis. M-85 and M-100 fuels contain 85 and 100 % methanol, respectively. Their high oxygen content leads to significant absorption of sulfur Kα radiation. To compensate for this, either correction factors must be applied or calibration standards matching the samples need to be used. Compared to other sulfur test methods, this method has high throughput, minimal sample preparation, and excellent precision. It is capable of determining sulfur over a wide range of concentrations. The equipment required, however, is significantly more expensive than for other methods.
TEST SUMMARY
A sample is placed in an X-ray beam, and the peak intensity of the sulfur Kα line at 5.373 Å is measured. The background intensity, measured at 5.190 Å is subtracted from the peak intensity. The resultant net counting rate is then compared to a previously prepared calibration curve or equation to obtain the sulfur concentration in mass percent.
TEST PRECISION
Where X is the mean sulfur concentration in mass %.
Case I includes distillates, kerosenes, residual oils, and crude oils.
Case II includes gasolines.
Gasohols were not included.
Case III included low level sulfur gasoline and diesel sample.
Based on the analysis of NIST SRM materials, there was significant bias in the analysis, but this was eliminated after correction for C/H ratio.