Globally, the permitted sulfur limit in fuel oils has been decreased to 10 ppm in many countries and regions. For compliance
verification, X-ray fluorescence (XRF) spectrometry is the definitive analysis tool for use at distribution terminal and refineries,
as well as mobile or stationary testing laboratories
Rigaku Micro-Z ULS is a benchtop wavelength dispersive X-ray fluorescence (WDXRF) spectrometer with fixed optics optimized
for sulfur analysis. The atmosphere in the optics path of the Micro-Z ULS is a vacuum so that helium gas is not required.
The spectrometer is designed to minimize the restrictions in installation such as cooling water, special power supply, installation
Micro-Z ULS is equipped with an air-cooled 40 W Cr-target X-ray tube and a doubly curved RX-9 analyzing crystal optimized
for low concentration sulfur. The counting time was 300 s for peak and background measurements. 4.0 mL of each diesel fuel
sample was poured into a liquid XRF cup (inner diameter 35 mm) equipped with 2.5 μm MylarŪ film.
Figure 1: Calibration results for diesel fuel.
Repeatability tests were carried out using a representative sample. For each, two aliquots were prepared and analyzed using
the calibration shown in Figure 1; this process was repeated 20 times. The test results are tabulated in Table I for diesel
fuel, in which the average and the difference of two aliquots are shown respectively. Lower-limit-of detection (LLD) was calculated
as 0.3 ppm sulfur.
Table I: Repeatibility results for diesel fuel
Low concentration sulfur in petroleum-based fuel can be routinely analyzed with high accuracy and precision with the Micro-Z
ULS, a benchtop WDXRF spectrometer with fixed optics, which does not require He gas, external water supply or special power
supply. This application note demonstrates that the performance of the Micro-Z ULS meets the requirements of ASTM D2622-10.
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