New AC TPI with Septum Purge

Significance of the Topic

The design of gas chromatographic inlets critically influences accuracy and robustness in simulated distillation (SIMDIS) analyses, where high-boiling analytes in volatile solvents can lead to sample discrimination, carry-over, and septum-related artifacts.

Objectives and Study Overview

This study introduces a new generation of AC Temperature Programmable Inlet (TPI) equipped with a septum purge feature. It aims to minimize carry-over, eliminate septum peaks, and enhance repeatability and boiling point determinations in ASTM D2887 and D7500 SIMDIS protocols.

Methodology and Instrumentation

The new septum purge design integrates a dedicated purge line adjacent to the inlet path and a flow control module to deliver a controlled carrier gas sweep beneath the septum, reducing dead volume and preventing residue buildup. The inlet chamber was precision-milled to avoid septum deformation.

Used Instrumentation

• AC Temperature Programmable Inlet (TPI) with Septum Purge Option
• AC SIMDIS Analyzer configured for ASTM D2887 and D7500 methods
• Flame Ionization Detector (FID) front and back signals for trace monitoring

Main Results and Discussion

• Blank runs after extensive use showed virtually no septum-derived peaks.
• Carry-over remained negligible even after multiple injections.
• Peak shapes improved, yielding sharper and more reproducible chromatographic profiles.
• Boiling point accuracy for True Boiling Point (TBP) and Final Boiling Point (FBP) fell within 1–2 °C of reference values across 0.5–99.5% mass cuts.

Benefits and Practical Applications

• Enhanced robustness and uptime for high-throughput SIMDIS laboratories.
• Reliable data for petroleum fractionation in refinery QA/QC.
• Simple retrofit capability on existing AC SIMDIS systems.

Conclusion

The AC TPI with Septum Purge significantly elevates SIMDIS performance by eliminating septum peaks, reducing carry-over, and improving boiling point determinations, thereby ensuring consistent and accurate analysis in petroleum refining applications.

Future Trends and Potential Applications

Further developments may explore automated flow control integration, adaptive purge algorithms linked to sample composition, and application to other high-boiling or reactive matrices, expanding the utility of septum purge in diverse GC methodologies.