EDXRF Analysis of Sulfur and Other Elements in Oil

Significance of the Topic

The accurate determination of sulfur and trace elements in fuel oils is critical for environmental compliance and pollution control. Sulfur compounds in fuel release SOx gases during combustion, contributing to acid rain and respiratory illnesses. Stricter regulations worldwide require reliable, rapid, and multi-element analytical methods to monitor sulfur and other elements in petroleum-based samples.

Objectives and Study Overview

This application note demonstrates the use of an energy dispersive X-ray fluorescence spectrometer (EDXRF) for simultaneous multi-element analysis of fuel oils. Using oil standards and a certified reference material (Conostan® S-21), the study aims to:

• Establish calibration curves for sulfur in helium and air atmospheres.
• Determine limits of detection (LOD) and quantitation (LOQ) for sulfur.
• Perform qualitative and quantitative analysis of trace elements in a commercial oil standard.

Methodology and Used Instrumentation

Sample Preparation:

• Approximately 6 mL of oil was poured into a sample cup and sealed with a 5 µm polypropylene film.

Instrument and Conditions:

• Instrument: Shimadzu EDX-720 energy dispersive XRF spectrometer
• X-ray Tube: Rhodium target
• Voltage and Current: 15 kV (auto µA) for light elements; 50 kV (auto µA) for heavier elements
• Filters: None for Al, Si, P; Filter #1 for Ca, Ti, V, Cr; #2 for Mn, Fe; #3 for Mo, Ni, Cu, Zn, Pb; #4 for Ag, Cd, Sn
• Atmospheres: Helium and air
• Measurement Diameter: 10 mm
• Measurement Time: 300 seconds per measurement
• Dead Time: Max 40%

Main Results and Discussion

Calibration and Sulfur Determination:

• Linear calibration curves for sulfur (SKα) were obtained in He and air (0–300 ppm range).
• LODs for sulfur were calculated as 5.9 ppm (He) and 13.0 ppm (air); LOQs were 19.9 ppm and 43.6 ppm, respectively.

Qualitative Analysis of Conostan® S-21:

• Spectrum profiles identified Al, Si, P, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Mo, Ag, Cd, Sn, and Pb.
• LODs for these elements ranged from 1.2 ppm (Pb Lα) to 31.0 ppm (Al Kα), demonstrating ppm‐level detection capability, particularly for heavier elements in air.

Benefits and Practical Applications

EDXRF offers rapid, non‐destructive, and simultaneous multi‐element analysis without complex sample digestion. The method supports routine quality control in refineries and environmental monitoring, ensuring compliance with sulfur limits and trace element specifications in fuels and lubricants.

Future Trends and Opportunities

Advances in detector technology and software algorithms will further lower detection limits and improve spectral deconvolution. Portable EDXRF systems can enable on‐site analysis of fuels and environmental samples. Coupling EDXRF with chemometric approaches could enhance speciation studies and accelerate regulatory testing.

Conclusion

The study validates the Shimadzu EDX-720 EDXRF spectrometer as an efficient tool for determining sulfur and a broad range of elements in fuel oils. Achieved detection limits meet regulatory requirements, offering a robust solution for environmental and industrial quality control.

Reference

Shimadzu Corporation, International Marketing Division, EDXRF Application Note No. X242A