Introduction of Liquid Samples using a Pyroprobe

Significance of the Topic

Liquid sample introduction into pyrolysis-GC systems is essential for retaining volatile and semi-volatile analytes, ensuring representative chromatographic profiles and efficient workflows in petrochemical, environmental and forensic laboratories.

Objectives and Study Overview

This application note contrasts two approaches for introducing liquid standards without detaching the Pyroprobe from the gas chromatograph. Using crude oil as a model matrix, the work aims to preserve early eluting components and demonstrate comparable performance between methods.

Methodology and Instrumentation

The study examines:

• Septum Injection Method: Injecting liquid directly into the heated interface at pyrolyzer port temperature for immediate transfer to the GC column or to a trap
• Tenax Microtrap Approach: Fabricating a quartz tube packed with Tenax and quartz wool plugs, loading the sample onto the sorbent and thermally desorbing it using the Pyroprobe coil

Used Instrumentation

Pyroprobe 5200 operational parameters:

• Interface temperature 325 °C for 4 minutes
• Filament heating 350 °C for 30 seconds
• Valve oven and transfer line at 325 °C
• Trap desorption at 325 °C for 4 minutes followed by reconditioning at 350 °C for 60 seconds

GC/MS settings:

• Column 30 m × 0.25 mm 5% phenyl methyl silicone
• Carrier gas Helium with 50:1 split
• Oven program 40 °C hold for 2 minutes then ramp 10 °C/min to 300 °C

Main Results and Discussion

Both injection strategies produced nearly identical crude oil chromatograms. Direct septum injection retained all volatile fractions, in contrast to sample losses observed when crude oil was simply placed in a quartz tube for later pyrolysis. The Tenax microtrap effectively captured low-boiling compounds and delivered them upon thermal desorption without significant loss.

Benefits and Practical Applications

• Enhanced recovery of volatile analytes for accurate quantification in complex matrices
• Reduced sample handling and risk of contamination by maintaining the Pyroprobe connection
• Flexibility to introduce liquid standards or environmental samples for calibration and validation

Future Trends and Opportunities

Advancements may include automated microtrap fabrication, integration with high-throughput autosamplers and adaptation to other sorbent materials for selective enrichment. Coupling with two-dimensional GC or high-resolution MS could further enhance detection of trace components.

Conclusion

Both heated septum injection and Tenax microtrap techniques enable reliable liquid sample introduction into a GC-Pyroprobe system while preserving volatile compounds. These methods offer robust alternatives for rapid analysis and method development in research and quality control laboratories.