Utilising unique TOF-MS technology and hydrogen carrier gas for fast GC-MS to produce robust, high quality, library comparable mass spectral data

Significance of the topic

Complex lipophilic extractives in wood samples comprise a wide range of resins, fatty acids, sterols and phenolic compounds which are critical to forestry research, materials science and quality control in industrial processing. Conventional one-dimensional GC/MS methods often fail to resolve coeluting compounds present at vastly different concentrations. Comprehensive two-dimensional GC coupled with time-of-flight mass spectrometry (GCxGC-TOFMS) expands chromatographic peak capacity and provides full-range, non-skewed spectral data, enabling the discovery and quantification of trace components in complex matrices.

Objectives and study overview

This work aimed to demonstrate how GCxGC-TOFMS enhances detection, separation and identification of lipophilic wood extractives compared to traditional one-dimensional approaches. Key goals included:

• Comparative evaluation of Soxhlet extractions using acetone and ethanol.
• Fractionation of extracts to isolate fatty acids, sterols and triglycerides.
• Illustration of GCxGC peak capacity gains and TOFMS deconvolution of closely eluting analytes.

Methodology

Wood samples from the USDA Forest Products Laboratory were prepared by conventional Soxhlet extraction. Six extracts were obtained using acetone and ethanol. Two of these were further fractionated with hexane or chloroform to concentrate sterols, sterol esters, triglycerides and fatty acids. The chemical classes targeted included:

• Resins and waxes
• Fatty materials and glycerides
• Alcohols
• Phenolic substances

Instrumental setup

GCxGC-TOFMS analysis was performed on an Agilent 7890 GC fitted with a LECO dual-stage quad jet thermal modulator coupled to a LECO Pegasus 4D TOFMS. Key parameters:

• Primary column: 30 m × 0.25 mm id × 0.25 µm Rxi-5SilMS
• Secondary column: 1.5 m × 0.1 mm id × 0.1 µm BPX-50
• Carrier gas: Helium at 1.5 mL/min
• Injection: 1 µL splitless or split 25:1, inlet 250 °C
• Primary oven program: 140 °C for 0.5 min, ramp 7 °C/min to 325 °C, hold 7 min
• Secondary oven: +5 °C offset, total run 39.5 min
• TOFMS range: m/z 45–650, acquisition rate 150 spectra/s, ion source 230 °C, detector 1650 V, electron energy –70 eV

Main results and discussion

GCxGC contour and 3D surface plots revealed critical separations of trace analytes otherwise buried in high-concentration peaks under one-dimensional GC. Examples include:

• Resolution of methyl abieta-8,11,13-trien-18-oate and docosahexaenoic acid methyl ester with only 7 ms separation in the second dimension.
• Enhanced detection of minor fatty acids, sterols and phenolics in acetone versus ethanol extracts.
• True signal deconvolution via ChromaTOF software generating pure mass spectra for coeluted compounds with library match scores above 74%.

Benefits and practical applications

GCxGC-TOFMS offers significant advantages for research and quality control:

• Comprehensive profiling of complex natural extracts.
• Identification of trace components for environmental and wood-chemistry studies.
• Improved analytical confidence through deconvoluted high-resolution mass spectra.
• Facile comparison of extraction protocols to optimize target analyte recovery.

Future trends and potential applications

Emerging directions include:

• Integration of high-resolution accurate mass spectrometry for elemental and isotopic analysis.
• Advanced software leveraging machine learning for automated peak detection and annotation.
• Application of GCxGC-TOFMS to other complex matrices such as biomass, food and environmental samples.
• Development of rapid modulation technologies to further boost peak capacity and reduce analysis time.

Conclusion

This proof-of-concept study confirms that GCxGC-TOFMS is a powerful analytical tool for the comparative analysis of wood Soxhlet extracts. The enhanced chromatographic resolution, increased peak capacity and robust deconvolution capabilities enable comprehensive characterization of lipophilic extractives that traditional methods cannot achieve. Adoption of this approach can significantly advance both academic research and industrial quality control in wood-derived materials.