Ultra Low Sulfur
In compliance with the ASTM D 4294-08 method at low concentrations sulfur.
This application note shows the excellent performance of Xenemetrix bench top analyzers, the X-Calibur and the S-Mobile ULS for ultra low sulfur determination in diesel according to the requirements of the ASTM method D4294-08.
The applicable concentration range for the ASTM method is from 17.0 ppm to 4.6 mass% . This note shows the performance at the very low concentration end from 0 to 25ppm.
Table 1: Analytical Configuration
|
Instrument |
|
|
X-Ray Tube |
Rh anode, 50kV/50W |
|
Detector |
Si PIN diode FWHM 160±10eV at 5.9keV |
|
Analysis time |
500s |
|
Atmosphere |
Helium purge |
|
Tube filter |
Thin film (Spectrolene) filter 16μm thickness |
EXPERIMENTAL
Five certified sulfur in diesel standards from VHS Labs were used to prepare a calibration curves between 0 to 25 ppm sulfur. The application was performed in Helium atmosphere 500 seconds. A thin XRF plastic film was used to reduce the background at the region of sulfur and to protect the X-ray tube window from diesel contamination. Each freshly prepared sample was measured twice. The correlation data, i.e. the calculated versus given concentration is plotted in a graph in Figure 1.
The correlation data is also tabulated in Table 2.
Table 2: Calibration data
|
Regression Analysis: Standard deviation 0.4ppm, Correlation 0.9988 |
||
|
Standard # |
Given standard sulfur |
Average calculated sulfur |
|
1 |
0 |
0.0 |
|
2 |
5 |
4.8 |
|
3 |
15 |
14.6 |
|
4 |
20 |
20.6 |
|
5 |
25 |
25.1 |
Figure 1: Sulfur in diesel correlation data
PRECISION
A repeatability study was performed on a 15 ppm sulfur in diesel solution. Ten consecutive
measurements were acquired and the result is presented in Table 3.
Table 3: Precision study on 15ppm sulfur in diesel
|
Sample ID |
Given conc. (ppm) |
Measured average conc. ± stand. dev. |
|
S_15 |
15 |
15.4±3.0 |
A typical spectrum of sulfur in diesel is presented in Figure 2. Although the Sulfur peak is hardly
observed the fit intensity method has no problem to extract the sulfur peak intensity as shpown by
the blue overlap in the spectrum in Figure 2.
Figure 2: The fit of the sulfur peak shown in a typical diesel spectrum (25ppm S)
DISCUSSION
This report shows that Xenemetrix EDXRF bench top analyzers can easily meet the requirement of
ASTM method D4294-08 and quantitatively measure sulfur in diesel at the very low end of the method i.e. from 5ppm and up.
