The Use of Resample to Improve Data Processing for GCxGC-TOFMS

Significance of the topic

Comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GCxGC-TOFMS) generates rich analytical datasets but also very large files because of high spectral acquisition rates, wide mass ranges, and long runs. Efficient handling of these datasets is essential for routine laboratory throughput and reliable automated processing. The Resample feature in ChromaTOF enables targeted creation of reduced data files that reduce processing time, improve spectral deconvolution, and can enhance sensitivity by matching acquisition density to peak widths.

Objectives and study overview

This application note demonstrates how ChromaTOF's Resample tool can be used with GCxGC-TOFMS data to:

• restrict processing to selected retention time windows,
• reduce effective acquisition (sample) rates by spectral summing,
• limit mass ranges to reduce file size and remove interfering ions, and
• assess impacts on file size, processing speed, spectral deconvolution, and sensitivity.

Two standard sample types were used: a petroleum PIANO mix (paraffins, iso-paraffins, aromatics, naphthenes, olefins) to illustrate targeted retention-time cropping and mass-range restriction, and a PBDE standard to illustrate how reducing the effective acquisition rate can improve response for broad, poorly chromatographed congeners such as BDE 209.

Methodology

Resample creates a new .peg file from an acquired sample file according to user-specified parameters: beginning and ending first-dimension retention times, beginning and ending mass (m/z) values, and a sample reduction rate (spectra-summing factor). Key characteristics:

• Extra spectra are summed rather than discarded when the sample reduction rate < 1 of original acquisition is chosen, which improves signal-to-noise ratio.
• The original raw file remains intact and can be reprocessed or re-sampled with different parameters.

Used instrumentation

Instrumentation details are provided separately for the two demonstration workflows.

• GCxGC platform (both studies): Agilent 6890 GC with LECO thermal modulator and secondary oven; data processed in LECO ChromaTOF; detector: LECO Pegasus TOFMS, electron ionization 70 eV.
• Petroleum (PIANO) method: Column 1: 100 m x 0.25 mm x 0.50 µm Rtx-1 PONA; Column 2: 2 m x 0.25 mm x 0.10 µm Rtx-50. Carrier He at 2.3 mL/min. Injection 0.05 µL split at 250°C, 250:1. Oven1: 40°C (0.2 min) then 2°C/min to 200°C; Oven2 offset +5°C. Modulation time 2 s. TOFMS: source 200°C, mass range 35–450 u, acquisition 100 spectra/s.
• PBDE method: Column 1: 9.5 m x 0.18 mm x 0.20 µm Rtx-5; Column 2: 1 m x 0.25 mm x 0.25 µm Rtx-Dioxin 2. Carrier He at 1.5 mL/min. Injection 1 µL direct at 250°C. Oven1: 120°C (1 min) then 10°C/min to 340°C (2 min); Oven2 offset +20°C. Modulation time 3 s. TOFMS: source 225°C, mass range 200–1000 u, acquisition 50 spectra/s.

Main results and discussion

Resample enables substantial file-size reductions and practical improvements in processing and sensitivity:

• PIANO example (targeting C3–C6 benzenes): The acquired file spanned 60–4810 s and m/z 35–450 with a file size of ~378 MB. Creating a resampled file restricted to 1850–3550 s and m/z 35–250 produced a new file of ~70 MB — an ~80% reduction. The original file remained available for other uses.
• Mass-range restriction reduces file size and can improve deconvolution by removing low or high m/z ions that stem from matrix interferences rather than analytes of interest.
• Sample reduction (spectra summing) can improve sensitivity when acquisition density is excessive relative to peak width. In the PBDE study, smaller PBDEs (e.g., BDE 47) produce narrow modulated slices (~200 ms) appropriate for 50 spectra/s, whereas BDE 209 produced very broad slices (~2 s). Oversampling BDE 209 at 50 spectra/s reduced apparent sensitivity. Using Resample to create files at lower effective acquisition rates (by factors of 2, 5, and 10 → 25, 10, and 5 spectra/s) increased peak responses for BDE 209 due to spectral summing, improving signal without altering the original acquisition.
• Figures and tables in the original report illustrate: the contour plot showing the selected first-dimension RT window, the Resample dialog and file-creation workflow, a table summarizing parameters and file sizes, and linear chromatograms comparing original vs. resampled acquisition rates for BDE 209. These show visual evidence of file-size reduction and improved peak shape/response when sample rate is matched to peak width.

Benefits and practical applications

Practical advantages of using Resample in GCxGC-TOFMS workflows include:

• Faster automated data processing and reduced computational load due to smaller files and narrower processing windows.
• Improved spectral deconvolution by excluding irrelevant m/z ranges associated with matrix noise or background.
• Enhanced sensitivity for broad chromatographic features by spectral summing to match acquisition density to peak width.
• Flexibility for targeted reprocessing: new files are derived from the original data without destructive changes, so multiple resampled datasets can be produced for different analysis targets.

Future trends and potential applications

Resample-type strategies are increasingly relevant as high-dimensional separations and rapid acquisition detectors become routine. Anticipated developments and applications include:

• Automated, intelligent resampling integrated into data workflows that select optimal spectral summing and mass-range windows based on peak detection and target lists.
• On-the-fly, instrument-linked resampling to reduce storage burden while preserving full-fidelity raw archives.
• Use in high-throughput laboratories to accelerate batch processing, QC, and screening tasks where only subsets of the chromatogram or limited mass ranges are required.
• Application to environmental, petrochemical, forensic, and food matrices where matrix ions complicate deconvolution, or where certain analytes require different acquisition densities for optimal quantification.

Conclusions

ChromaTOF's Resample feature provides a practical, non-destructive approach to tailor GCxGC-TOFMS datasets for faster processing and improved analytical performance. By limiting retention-time windows, trimming mass ranges, and reducing sample rates through spectral summing, users can substantially decrease file sizes, speed automated routines, improve deconvolution, and in some cases increase sensitivity for broad chromatographic peaks. The original raw files are preserved, enabling flexible reprocessing strategies.

References

• LECO Corporation. The Use of Resample to Improve Data Processing for GCxGC-TOFMS. Application note, LECO Corporation, St. Joseph, MI, 2008.