Direct Thermal Extraction Analysis of Solid and Liquid Samples using the GERSTEL MPS Robotic Sampler, Thermal Desorption Unit (TDU 2) and Cooled Inlet System (CIS)

Importance of the Topic

Direct thermal extraction (DTE) combined with thermal desorption–GC/MS offers a rapid, solvent-free approach to analyze volatile and semi-volatile organic compounds in solid and liquid matrices. This technique is particularly valuable for quality control and product development in fragrance industries, environmental VOC monitoring, and troubleshooting off-notes in consumer products. Its minimal sample preparation and compatibility with automated systems make DTE a versatile tool for trace analysis and real-time monitoring of aroma emissions.

Objectives and Study Overview

This study demonstrates the application of the GERSTEL MultiPurpose Sampler (MPS) with a Thermal Desorption Unit (TDU-2) and Cooled Inlet System (CIS-4) for two purposes: direct thermal extraction of pumpkin-spice scented wax samples and quantitative air sampling of key aroma compounds. Three commercially available candle brands were compared, focusing on the release profiles of limonene, linalool, and eugenol in confined indoor air.

Used Instrumentation

• Agilent 7890A Gas Chromatograph coupled to a 5977B Mass Selective Detector
• GERSTEL MPS robotic sampler equipped with TDU-2 and CIS-4
• Thermal desorption tubes: empty fritted tubes and Tenax-TA® sorbent tubes
• Sampling pump with Teflon tubing and Swagelok fittings for air collection

Methodology

Solid wax samples (10–50 mg) were placed in micro-vials inside empty TDU tubes and desorbed under splitless conditions. The TDU ramped from 40 °C to 100 °C, transferring analytes into the CIS inlet held at –120 °C. After trapping on glass wool, compounds were released to the GC column via rapid CIS heating. Air sampling was performed in a 9×13×10 ft room using Tenax-TA tubes at 25 mL/min for 20 min every hour over 4 h. Calibration curves for limonene, linalool, and eugenol (0.3–30 ng/mL) were generated by spiking standards onto sorbent tubes under identical desorption conditions.

Main Results and Discussion

Direct extraction chromatograms revealed distinct aroma profiles: Brand A exhibited the richest mixture (monoterpenes, benzene derivatives, additives, alkane wax residues), Brand B showed the highest limonene and eugenol peaks plus common diluents, while Brand C demonstrated fewer peaks dominated by benzaldehyde derivatives. Air monitoring data correlated with DTE findings: limonene release increased over time for brands A and B (highest in B), remained low in C; linalool levels were stable or slowly rising (highest in C); eugenol concentrations decayed due to oxidative loss. Trendline fits illustrated release rates and concentration changes, highlighting compound-specific behavior during candle combustion.

Benefits and Practical Applications

• Minimal or no solvent use and reduced sample handling
• High sensitivity for trace VOCs and semi-VOCs
• Automated, reproducible workflows for QC and batch consistency checks
• Capability to identify off-notes and formulation defects rapidly
• Simultaneous analysis of solid samples and ambient air for comprehensive product evaluation

Future Trends and Potential Applications

The DTE-GC/MS approach may evolve through integration with advanced sorbents for broader compound classes, coupling with real-time detectors (e.g., PTR-MS) for kinetic studies, and miniaturized consumer-grade samplers for indoor air quality monitoring. Machine learning–driven data analysis could further refine fragrance profiling and predictive quality assessments. Method standardization across industries will expand its use in regulatory compliance and environmental health studies.

Conclusion

The combination of GERSTEL MPS, TDU, and CIS platforms provides a robust, automated solution for direct thermal extraction of scented waxes and quantitative monitoring of aroma compounds in air. The strong agreement between DTE chromatograms and ambient concentration profiles underscores its value for fragrance research, product development, and quality assurance in consumer goods.

Reference

• Air Sampling of Fragrance Compounds using the Automated GERSTEL Gas Sampling System (GSS), GERSTEL AppNote 5/2014.