Analysis of Sulfur Compounds in Light Petroleum Liquids Using ASTM Method D5623

Importance of the Topic

The detection and speciation of volatile sulfur compounds in light petroleum liquids is critical due to their impact on product quality, equipment corrosion, catalyst poisoning, and environmental emissions. Gas chromatography combined with a pulsed flame photometric detector offers enhanced sulfur selectivity and sensitivity, enabling reliable identification and quantification of sulfur species at low concentrations.

Objectives and Study Overview

This work demonstrates the implementation of ASTM Method D5623 using a new generation pulsed flame photometric detector to analyze light petroleum distillates with boiling points up to 230 °C. The study aims to establish a robust, sensitive protocol for both total and speciated sulfur measurement in light hydrocarbons, meeting forthcoming regulatory requirements such as the USEPA Tier 3 fuel standards.

Methodology

• Eight-point calibration covering 0.1 to 10 ppm for major sulfur compounds with linear regression coefficients (R2) exceeding 0.998
• Manual injection of 1 µL calibration and sample standards prepared in 90% isooctane and 10% toluene
• System suitability checks including method system test mixture and matrix blank analysis to ensure stability and reproducibility

Used Instrumentation

• Gas chromatograph: Agilent 7890A with split/splitless inlet at 250 °C, split ratio 10:1
• Detector: OI Analytical Model 5383 pulsed flame photometric detector operated in linearized sulfur mode
• Column: Restek Rxi-1 ms, 30 m × 0.32 mm ID × 4.0 µm film thickness, helium carrier gas at 1.0 mL/min
• Oven temperature program: 40 °C (2 min) → 10 °C/min to 100 °C (8 min) → 30 °C/min to 300 °C (2 min)

Main Results and Discussion

The method achieved equimolar sulfur response for all target analytes, allowing accurate quantitation of unknown species. Calibration curves showed excellent linearity (R2 ≥ 0.998), while gas chromatograms of two gasoline samples revealed distinct sulfur profiles, with individual mercaptans and thiophenes quantified in the 0.16 to 13.7 ppm range. Co-elution of sulfur dioxide and carbonyl sulfide was noted but resolved in the sulfur channel.

Benefits and Practical Applications

• Enhanced sulfur selectivity minimizes matrix interferences from hydrocarbons
• High sensitivity supports trace-level detection down to 0.1 ppm
• Equimolar response simplifies quantitation of novel or unknown sulfur species
• Compliance with ASTM D5623 provides a standardized framework for quality control in fuel production

Future Trends and Potential Applications

Advances may include coupling pulsed flame photometric detection with mass spectrometry for compound confirmation, miniaturized GC-PFPD platforms for field testing, and expanded method adaptation to heavier petroleum fractions and biofuels. Automation and data analytics integration can further enhance throughput and accuracy.

Conclusion

The combination of ASTM D5623 with a modern pulsed flame photometric detector delivers a reliable, sensitive, and selective approach for speciation and quantitation of sulfur compounds in light petroleum liquids, supporting regulatory compliance and product quality improvement.

References

• ASTM D5623-94 (2014) Standard Test Method for Sulfur Compounds in Light Petroleum Liquids by Gas Chromatography and Sulfur Selective Detection, ASTM International.