The Use of Different PTV Inlet Liner Types for Trapping Alkanes, Aromatics and Oxygenated Compounds During Thermal Desorption

Significance of the topic

Pre-focusing analytes prior to GC separation greatly improves sensitivity and chromatographic performance, especially for complex air samples or high-flow introductions such as thermal desorption. Selecting an optimal PTV inlet liner and trapping conditions is critical when the target analytes cover a wide boiling point range and include alkanes, aromatics, and oxygenated VOCs. Appropriate trapping reduces column contamination, prevents moisture freeze-up, and extends column lifetime.

Objectives and overview of the study

This work evaluates various PTV inlet liner types to identify the best configurations for trapping and refocusing alkanes (C7–C16), aromatics, and oxygenated compounds (BP 80–290 °C) during thermal desorption GC–MS. The study compares inert supports (glass wool, quartz wool), adsorbent packed liners (Tenax TA™, Carbotrap™), and custom multi-bed liners under different cryo-focussing temperatures and desorption flows.

Methodology and Instrumentation

All analyses were performed on an Agilent 6890 GC with 5973 MS, equipped with a Gerstel TDS 2 thermal desorption system and CIS4 PTV inlet. Standard mixtures of 14 VOCs (alkanes, aromatics, oxygenates) at 2 mg/mL in hexane were spiked onto Tenax TA™ tubes, purged with helium (400 mL/min, 8 min), and desorbed under varying conditions:

• Cryo-focussing: –150 °C, –40 °C, 10 °C
• Desorption flow: 30, 50, 70 mL/min

The performance of each liner was assessed by peak area, peak shape, and carry-over behavior.

Main results and discussion

Inert supports: Deactivated glass wool at –150 °C and 30 mL/min provided best overall trapping and sharp peaks for most analytes. Quartz wool and silanized glass wool showed slightly lower efficiency but remained stable.

Adsorbent liners: Tenax TA™ performed well for aromatics and oxygenates at –40 °C and 70 mL/min but gave poor recovery for C14–C16 alkanes due to incomplete desorption. Carbotrap™ liners delivered improved recovery of long-chain alkanes and consistent trapping across analytes at 10 °C and 50 mL/min. Mixed Tenax–Carbotrap liners behaved similarly to pure Tenax, reflecting the inlet’s flow-order effect.

Peak shape: Strong adsorption on polymeric adsorbents led to broadened or split peaks under the study’s high split ratio (30:1). The inert deactivated glass wool liner consistently yielded the sharpest peaks and the least carry-over.

Benefits and practical applications of the method

The optimized approach allows reliable quantitation of a broad range of VOCs from air sampling tubes with high sample loads and minimal column fouling. Using deactivated glass wool liners and cryo-focussing at –150 °C maximizes sensitivity for alkanes, aromatics, and oxygenates, while adsorbent liners permit trapping without cryogen when cooler limits or moisture are concerns.

Future trends and potential applications

Development of advanced multi-bed liner materials may further tailor trapping selectivity. Integration with automated thermal desorption workflows and sub-ambient Peltier cooling will expand applicability to ultra-volatile and highly polar analytes. Coupling optimized inlet liners with two-dimensional GC or improved MS detectors could push detection limits for environmental and industrial VOC monitoring.

Conclusion

PTV inlet liner selection and trapping conditions are pivotal for comprehensive thermal desorption GC analysis. Deactivated glass wool liners at –150 °C and moderate flow provide the best compromise of peak shape and recovery across C7–C16 alkanes, aromatics, and oxygenates. When cryogenic cooling is limited, Tenax TA™ or Carbotrap™ liners offer acceptable performance with tailored desorption parameters.

Reference

No additional literature references were provided in the original document.