Halogens and sulfur in LPG according to ASTM D7994

Significance of the topic

Determination of halogens and sulfur in liquefied petroleum gas is crucial for quality control, regulatory compliance, and safety in fuel production and distribution.

Objectives and overview of the study

This study demonstrates the application of ASTM D7994 for quantifying fluorine, chlorine, bromine, and sulfur in an LPG matrix. A synthetic butane sample is analyzed to validate precision, accuracy, and robustness of the method using modern combustion ion chromatography techniques.

Methodology

The LPG sample is introduced via a dedicated module into an oxidative pyrohydrolytic combustion system. Combustion occurs at high temperature, converting analytes into soluble ionic forms. Post-combustion, an absorber solution captures the combustion products. Ion chromatography employing intelligent Partial Loop Injection and Inline Matrix Elimination separates and quantifies the target ions. Parameters include high-temperature oven operation, controlled gas flows, and precise dosing of absorption and rinse solutions.

Instrumentation used

• Combustion Oven with LPG Module for sample introduction and high-temperature pyrohydrolysis
• 920 Absorber Module for post-combustion absorption and transfer
• 930 Compact IC Flex with conductivity detector for ion separation and detection
• 800 Dosino units for dosing of absorber solution, rinse water, and pyrohydrolytic water
• MSM Rotor A and suppressor accessories for eluent suppression and flow management

Key results and discussion

• Fluorine: 26.33 mg/kg with 1.5% RSD
• Chlorine: 17.23 mg/kg with 1.1% RSD
• Bromine: 37.83 mg/kg with 1.2% RSD
• Sulfur: 13.08 mg/kg with 0.5% RSD

Nitrite and nitrate peaks were observed but not quantified. The method exhibits excellent repeatability and sensitivity in the low mg/kg range. Inline matrix elimination and partial loop injection enhance accuracy by minimizing matrix effects and improving injection precision.

Benefits and practical applications of the method

This approach offers rapid, sensitive, and reproducible analysis of trace halogens and sulfur in LPG. It supports quality assurance in fuel production, regulatory monitoring of contaminant levels, and research into fuel formulation and emission control.

Future trends and potential applications

Integration with automated sampling and data processing will further reduce analysis time and operator intervention. Advances in detector technology and column chemistries may extend the method to additional analytes and complex matrices. Portable and field-deployable combustion IC systems could enable on-site monitoring of fuel composition.

Conclusion

The application of ASTM D7994 with combustion ion chromatography delivers reliable quantification of halogens and sulfur in LPG. High precision, minimal sample preparation, and robust instrumentation make this method well suited for industrial and regulatory laboratories.

References

• ASTM D7994 17 Standard Test Method for Determination of Halogens and Sulfur in LPG
• Metrohm Application Note CIC 023 Version 1 July 2017