Analysis of certified LPG applying Metrohm Combustion IC with a nested method setup

Significance of the Topic

The accurate quantification of fluorine and sulfur in liquefied petroleum gas (LPG) is essential for ensuring product quality, meeting safety standards, and controlling emissions. Trace levels of these elements can impact combustion behavior and catalyst performance in downstream processes. Implementing a robust analytical method enhances process control and regulatory compliance for industrial and commercial LPG applications.

Objectives and Study Overview

This study demonstrates the application of Metrohm Combustion Ion Chromatography (Combustion IC) to determine certified levels of fluorine and sulfur in LPG. A nested analysis sequence is employed to maximize throughput by performing combustion of the next sample while the previous one is analyzed by ion chromatography. The method is validated using certified reference samples of liquefied butane containing known amounts of dimethyl sulfide or fluorobenzene.

Methodology and Instrumentation

The analytical workflow combines combustion, absorption, and ion chromatographic separation with the following key features

• Combustion of LPG samples at 1050 °C using oxygen and argon flows
• Absorption of combustion products in hydrogen peroxide solution
• Partial Loop Injection with Inline Matrix Elimination for sample introduction
• Ion separation on Metrosep A Supp 16 and Metrosep A PCC columns
• Conductivity detection after sequential suppression

Used Instrumentation

The following Metrohm modules were employed in this nested method setup

• 930 Compact IC Flex Oven/SeS/PP/Deg
• IC Conductivity Detector
• 920 Absorber Module
• Combustion Module (oven and gas module)

Results and Discussion

Using nine replicate measurements for each analyte, the method yielded mean concentrations of 411 mg/kg for fluorine and 456 mg/kg for sulfur. The associated relative standard deviations were 2.6% and 4.0%, respectively. These precision values demonstrate reliable repeatability. The nested approach reduced idle times by overlapping combustion and chromatographic steps, enhancing throughput without compromising analytical performance.

Benefits and Practical Applications

The nested Combustion IC offers several advantages for routine LPG analysis

• Increased sample throughput through parallel processing
• Minimal sample handling and reduced risk of contamination
• High sensitivity and selectivity for halogen and chalcogen detection
• Automated workflow compatible with quality assurance and regulatory labs

Future Trends and Potential Applications

Advancements may include integration of machine learning for method optimization, expansion to multi‐element combustion analysis, and miniaturization of modules for field applications. The nested concept could be adapted to other complex matrices, further improving laboratory efficiency.

Conclusion

The nested Combustion IC method provides an efficient, accurate, and reproducible solution for determining fluorine and sulfur in LPG. Its high throughput and robust performance make it suitable for industrial quality control and environmental monitoring.

References

No external literature references were provided in the original application note.