Ultra-low sulfur in automotive fuels according to ASTM D2622 with high power WDXRF spectrometer

Significance of the Topic

The reduction of sulfur content in automotive fuels is critical to meet stringent emission regulations worldwide. Ultra-low sulfur diesel (ULSD) limits have been lowered to 10 ppm to protect catalytic converter materials and reduce sulfur oxides (SOx) and fine particulate emissions. Fast, accurate methods for quantifying trace sulfur in fuels are essential for quality control and regulatory compliance.

Objectives and Overview of the Study

This application note evaluates the performance of the Thermo Scientific ARL PERFORM’X 4200W WDXRF spectrometer for measuring ultra-low sulfur levels in diesel and gasoline in accordance with ASTM D2622-16. The goal is to demonstrate ease of sample preparation, precision, detection limits, and compliance with regulatory requirements.

Instrumentation Used

• Wavelength-dispersive X-ray fluorescence spectrometer: Thermo Scientific ARL PERFORM’X 4200W
• X-ray tube: 5GN+ Rh with 50 µm Be window and dual water cooling
• Analyzing crystal: PET
• Detector: Flow proportional counter (FPC)
• Collimator: Medium (0.4°)
• Sample environment: Helium purge and LoadSafe liquid handling system
• Operating conditions: 30 kV, 80 mA

Methodology

Standard solutions were prepared by diluting a 0.300 % S certified reference material into blank oil to yield 2.5, 4, 14, and 20 ppm sulfur. A blank oil sample defined the background. Measurement settings were optimized to maximize the S Kα peak‐to‐background ratio, using a PET crystal and medium collimator. One background point was included in the calibration. Counting times were set to 100 s for detection limit determination and up to 120 s for routine measurements.

Main Results and Discussion

The calibration curve for sulfur exhibited excellent linearity from 0 to 20 ppm, with a sensitivity of 351 kcps/% and a calculated detection limit of 0.1 ppm at 100 s counting time. Repeatability tests on gasoline (∼7.3 ppm S) and diesel (∼8.7 ppm S) samples yielded relative standard deviations below 2 % and maximum run-to-run differences within 0.72 ppm and 0.83 ppm, respectively, meeting ASTM D2622-16 precision criteria. The instrument’s stability and safety features, including automated liquid ejection and vacuum protection, support reliable long-term operation.

Benefits and Practical Applications

• Rapid sample preparation without digestion or chemical pretreatment
• High precision and low detection limits suitable for regulatory compliance
• Automated safety and liquid handling reduce operator risk and downtime
• Applicable to routine quality control and research in fuel analysis laboratories

Future Trends and Opportunities for Use

Advances in XRF detector technology and software integration may further lower detection limits and improve throughput. Potential developments include automation of sample changers, enhanced spectral deconvolution for complex matrices, and expansion to sulfur analysis in biofuels and alternative fuels. Integration with laboratory information management systems (LIMS) will streamline data reporting and regulatory record-keeping.

Conclusion

The ARL PERFORM’X 4200W WDXRF spectrometer delivers accurate, precise, and interference-free measurement of ultra-low sulfur in automotive fuels according to ASTM D2622-16. Its rapid analysis, robust safety features, and compliance with regulatory requirements make it an ideal tool for fuel quality control and environmental monitoring.