Comparing glass and deactivated stainless steel sample cups - Part 2 Analysis of fatty acids in Salmonella by reactive Py-GC/MS

Importance of the Topic

Reaction pyrolysis coupled with GC/MS provides a rapid and direct approach for profiling complex lipid mixtures in microbial samples. Ensuring the sample cup material does not influence methylation or detection of fatty acids is critical for accurate quantitative analysis, quality control, and comparative studies in environmental and food microbiology.

Study Objectives and Overview

This study compares glass (Eco-cup G) and deactivated stainless steel (Eco-cup) pyrolysis cups to assess their impact on the reactive pyrolysis methylation and distribution of fatty acids extracted from Salmonella typhimurium LT2. The goal is to determine if cup surface chemistry affects analytical results during quantitative RxPy-GC/MS.

Methodology

• Sample Preparation: 30 µg of lyophilized Salmonella typhimurium LT2 mixed with 6 µL of tetramethylammonium hydroxide in 25 wt % methanol.
• Reactive Pyrolysis: Samples pyrolyzed at 400 °C using a Multi-Shot Pyrolyzer directly interfaced to a GC/MS split injection port.
• Chromatographic Conditions: UA-CW capillary column (length 30 m, inner diameter 0.25 mm, film thickness 0.25 µm); oven ramp from 50 °C to 180 °C at 5 °C/min (20 min hold), then to 220 °C at 5 °C/min.
• Detection: Separation of methyl esters of fatty acids followed by mass spectrometric detection.

Instrumental Setup

• Multi-Shot Pyrolyzer (EGA/PY-3030D)
• Gas chromatograph with split/splitless injection port
• UA-CW capillary column (30 m × 0.25 mm × 0.25 µm)
• Tetramethylammonium hydroxide (TMAH) reagent

Main Results and Discussion

Reactive pyrolysis GC/MS chromatograms for both cup types showed nearly identical profiles of fatty acid methyl esters. Quantitative comparison of peak areas revealed minor differences in molar percentages across C12:0, C14:0, C16:0, C16:1, C17:0, cyclic C17, C18:0, and C18:1, all within experimental variability. These findings confirm that neither glass nor deactivated stainless steel surfaces alter fatty acid methylation or distribution under the tested conditions.

Benefits and Practical Applications

• Choice of cup material does not compromise quantitative lipid analysis.
• Flexibility for laboratories to select glass or stainless steel pyrolysis cups based on availability or preference.
• Improved reliability for routine QA/QC, environmental monitoring, and microbial lipidomic profiling.

Future Trends and Potential Applications

• Development of novel cup coatings to minimize background and expand analyte compatibility.
• Integration with high-throughput automation for large-scale lipidomics and microbial diagnostics.
• Application in targeted biomarker screening, food safety, and industrial microbiology.

Conclusion

The comparative study demonstrates that both glass and deactivated stainless steel sample cups yield equivalent fatty acid profiles in Salmonella when using reactive pyrolysis GC/MS with TMAH methylation. This establishes the robustness of RxPy-GC/MS methods regardless of cup material, supporting its routine use in analytical laboratories.

References

• Y. Ishida et al., Journal of Analytical and Applied Pyrolysis 77 (2006) 116-120