Halogens in LPG applying Metrohm Combustion IC

Significance of the Topic

Accurate determination of halogens in liquefied petroleum gas (LPG) is critical for product quality control, equipment integrity and compliance with environmental regulations. Fluorine and chlorine residues can originate from production or processing additives and may affect burner performance, catalyst life and exhaust emissions.

Study Objectives and Overview

This application note demonstrates a combustion ion chromatography (CIC) method for simultaneous quantification of fluorine, chlorine, bromine and sulfate in an LPG sample composed of butane and propane. The approach aims to deliver low detection limits, high precision and minimal sample preparation through an inline matrix elimination strategy.

Methodology and Instrumentation

The sample (50 µL LPG) is introduced via an LPG/GSS injection module into a high-temperature combustion chamber. Complete oxidation at 1050 °C converts organic halogen species into inorganic anions, which are then trapped in an absorption solution containing hydrogen peroxide. Post-combustion, the aqueous extract is transferred to an ion chromatograph employing intelligent Partial Loop Injection Technique (MiPT) with inline matrix removal to protect the separation column and detector.

Used Instrumentation

• 930 Compact IC Flex with Combustion Module and Oven/Gas System
• IC Conductivity Detector
• MSM Rotor A for MiPT
• 920 Absorber Module
• Metrosep A Supp 5 and A Supp 4/5 Guard columns
• Metrosep A PCC 1 HC pre-column
• LPG/GSS Module for direct gas injection

Main Results and Discussion

Repeat injections (n = 5) yielded average concentrations of 1.88 µg/g fluorine (RSD 1.2 %) and 1.85 µg/g chlorine (RSD 0.9 %). Bromine was below the detection threshold, and sulfate was determined at 0.15 µg/g (RSD 1.2 %). The precision and low background demonstrate the reliability of inline matrix elimination and the robustness of the combustion-IC setup.

Benefits and Practical Applications

• Minimal sample preparation with direct gas injection reduces analysis time and risk of contamination.
• Simultaneous multi-analyte detection streamlines quality control workflows for petrochemical products.
• High precision and low detection limits support compliance monitoring and catalyst maintenance strategies.

Future Trends and Potential Applications

Emerging developments include expanded element panels for sulfur speciation and metal halides, integration with automated sampling systems for continuous monitoring and adaptation of combustion-IC to other gaseous or liquid hydrocarbon matrices. Advances in detector technology and software are expected to further enhance sensitivity and throughput.

Conclusion

The described CIC method offers a robust, reliable solution for quantifying trace halogens and sulfate in LPG. The combination of high-temperature combustion, inline matrix elimination and advanced injection techniques ensures accurate results with minimal manual intervention, making it well-suited for industrial and regulatory laboratories.