Analysis low volatility samples using high temperature PTV injection

Significance of the Topic

High temperature capillary gas chromatography (HT-GC) enables separation and analysis of thermally stable compounds with molecular weights up to 1500 Dalton. This extension beyond conventional GC opens new analytical possibilities for polymer additives, hydrocarbon oils, surfactants and triglycerides, which were previously accessible only by liquid chromatography or supercritical fluid chromatography.

Objectives and Overview of the Study

The study examines programmed-temperature vaporization (PTV) injection at elevated final temperatures (up to 600 °C) as a discrimination-free sample introduction technique in HT-GC. It compares high-temperature PTV (HT-PTV) with on-column injection, evaluates reproducibility of retention times and peak areas, and assesses quantitative transfer of low-volatility samples.

Methodology and Instrumentation

• Instrument: HP 5890-A GC with AI Cambridge OPTIC high-temperature PTV injector and FID detector
• Column: 8 m × 320 μm Chrompack SimDist capillary with dimethylsilicone phase; oven 40 °C to 400 °C at 20 °C/min
• PTV program: 35 °C to 599 °C at 8 °C/s; nitrogen makeup gas; detector at 400 °C
• On-column reference: special insert replacing split liner on the same GC
• Test samples: polymer additives, hydrocarbon waxes (Polywax 655, 1000), triglycerides (milk chocolate extract), ethoxylated surfactants (Triton X-100)

Results and Discussion

• Polymer Additives: A final PTV temperature of ~600 °C was required to transfer high-boiling Irganox 1010; at 400 °C this component failed to elute. HT-PTV matched on-column retention times (RSD < 0.2%) and relative peak areas (RSD up to 4%).
• Hydrocarbon Waxes: HT-PTV at 599 °C provided narrow peaks for Polywax 655 and a distribution up to C100, consistent with on-column injection.
• Triglycerides: Milk chocolate extracts yielded accurate quantification of POP, POS and SOS triglycerides (≈19%, 47%, 33%), in agreement with on-column results, without need for a retention gap.
• Surfactants: HT-PTV enabled direct analysis of Triton X-100, displaying a Gaussian oligomer distribution centered at ~10 ethoxylate units, matching SFC data.

Benefits and Practical Applications of the Method

• Discrimination-free introduction of high molecular weight compounds
• Elimination of retention gaps and associated leak risks
• Enhanced automation and reduced maintenance: contaminated liners can be replaced more easily than column segments
• Versatility for diverse low-volatility samples in industrial QA/QC, environmental analysis and research laboratories

Future Trends and Potential Applications

• Coupling with mass spectrometry for improved detection and structural insight
• Development of more robust liners and inert inlet surfaces to withstand ultra-high temperatures
• Automation of sample preparation and PTV injection, including SPME integration
• Extension of HT-GC to larger macromolecules and complex polymer or lipid mixtures

Conclusion

High-temperature PTV injection offers a robust, discrimination-free approach for introducing thermally stable, low-volatility samples into GC at temperatures up to ~600 °C. It achieves reproducible retention times and relative quantification comparable to on-column methods while simplifying automation and maintenance, broadening the applicability of GC in analytical chemistry.

Reference

• No formal references were listed in the original text.