Determination of 16 Volatile Organic Compounds and TVOC in Indoor Air by Thermal Desorption-Gas Chromatography

Importance of the Topic

The accurate measurement of volatile organic compounds (VOCs) and total volatile organic compounds (TVOC) in indoor air is critical for assessing human exposure, ensuring compliance with building environment standards, and guiding mitigation strategies. Thermal desorption–gas chromatography (TD–GC) is a widely accepted approach for low-level VOC monitoring because it concentrates analytes collected on sorbent tubes and enables sensitive analysis without solvent extraction. The method described leverages a multi-mode inlet (MMI) to perform direct thermal desorption in the GC inlet, offering a compact and cost-effective workflow suitable for routine indoor air surveillance and regulatory compliance testing.

Objectives and Study Overview

This application study aimed to develop and validate a TD–GC method on the Nexis GC-2060 (Shimadzu) for the simultaneous determination of 16 target VOCs and TVOC in indoor air in accordance with the Chinese mandatory standard GB 50325-2020. Key goals were to demonstrate: method sensitivity and linearity across a working range, repeatability at low mass loadings, achievable method detection limits (MDLs) for a 5 L sampling volume, and practical performance on real indoor air samples.

Methodology

Sampling and sample preparation:

• Air samples were collected on Tenax TA sorbent tubes using a pump at 500 mL/min to obtain a 5 L sample volume per tube.
• Calibration tubes were prepared by injecting methanolic mixed standards onto Tenax TA tubes and purging with nitrogen to produce tubes containing 50–2000 ng per compound.

Chromatographic and desorption conditions (summary):

• Instrument: Nexis GC-2060 with a multi-mode inlet (MMI) operated in thermal desorption/extraction injection mode; split ratio 10:1.
• Column: RTX-1 (nonpolar), 50 m × 0.25 mm × 0.25 µm film.
• Carrier gas: helium, linear velocity ~22 cm/s.
• Inlet thermal program: initial 35 °C then rapid ramp to 260 °C for desorption.
• Oven program: 50 °C hold (10 min), ramp 6 °C/min to 260 °C (5 min hold).
• Detection: Flame ionization detector (FID), detector temp 280 °C; make‑up He 30 mL/min, H2 40 mL/min, air 170 mL/min.

Calibration and quantitation:

• External calibration using standard tubes at 50, 100, 400, 800, 1200, and 2000 ng per compound.
• Linearity assessed across the 50–2000 ng range, with response factors used to quantify environmental samples; co-elution of p‑ and m‑xylene was handled by combined integration.

Used Instrumentation

• Nexis GC-2060 gas chromatograph (Shimadzu) with MMI supporting thermal desorption/extraction mode.
• RTX-1 capillary column (50 m × 0.25 mm × 0.25 µm).
• Tenax TA sorbent tubes for air sampling.
• Gas sampling pump for controlled-volume collection (500 mL/min).
• Flame ionization detector (FID) with specified gas flows.

Main Results and Discussion

Analytical performance:

• All 16 target VOCs exhibited excellent linearity across the tested range with correlation coefficients typically >0.998, demonstrating reliable quantitation from 50 ng to 2000 ng per tube.
• Repeatability (six replicate analyses at 50 ng per compound) produced relative standard deviations (RSDs) between ~2.7% and 7.4%, indicating good precision for low-level measurements.
• Method detection limits (calculated from three times baseline noise for 50 ng tubes and converted to a 5 L sampling volume) ranged from approximately 0.25 to 4.72 µg/m3, satisfying the MDL requirements specified in Appendix E of GB 50325-2020 for TVOC testing.
• Chromatographic notes: p- and m-xylene co-eluted under the chosen conditions and were integrated together for quantitation; this is a common limitation when using a single nonpolar column and FID detection.

Application to real samples:

• An indoor air sample (5 L) analyzed with the developed method yielded a TVOC concentration of 1360 µg/m3. Individual analytes were mostly low or not detected; n‑hexane was notably high at ~1340 µg/m3 in the reported sample, while several heavier aliphatics were below detection.
• Unidentified peaks equivalent to 12.3 µg/m3 were present and were quantified using a toluene response factor for TVOC summation, reflecting the limitation of FID for compound identification.

Benefits and Practical Applications

• The MMI thermal desorption/extraction mode enables direct placement of sorbent tubes into the GC inlet for desorption, removing the need for a separate dedicated thermal desorber—this simplifies the workflow, reduces instrument footprint, and lowers capital cost.
• The method provides sufficient sensitivity, precision, and linearity for regulatory indoor air monitoring per GB 50325-2020, making it suitable for building inspections, indoor air quality surveys, and compliance testing.
• Using Tenax TA with TD–GC-FID allows solventless sample handling and rapid turnaround for routine analysis.

Limitations and Considerations

• FID detection offers robust quantitation but limited compound specificity; co-elutions and unknown peaks cannot be confidently identified without mass spectrometric detection.
• Tenax TA is less suitable for highly volatile or highly polar compounds; breakthrough and artifact formation should be considered during sampling and storage.
• Quantification of unidentified compounds by applying a toluene correction factor introduces uncertainty in TVOC summation; targeted identification may require TD–GC–MS.

Future Trends and Applications

• Integration with mass spectrometric detection (TD–GC–MS) or high-resolution MS would provide compound-level identification for unknowns and resolve co-elutions, improving TVOC source apportionment and health-risk evaluation.
• Automation of sorbent tube handling and TD injection can increase throughput and reduce operator variability for large-scale monitoring programs.
• Development of multi-sorbent tubes and optimized thermal programs will broaden the detectable compound range (very volatile to semi-volatile) and minimize sampling artifacts.
• Advances in data processing and spectral libraries tailored to indoor air will facilitate rapid identification of emerging contaminants and complex mixtures.

Conclusion

The Nexis GC-2060 equipped with an MMI operating in thermal desorption/extraction mode provides a compact and effective platform for TD–GC analysis of 16 target VOCs and TVOC in indoor air. The method demonstrated strong linearity, adequate repeatability at low mass loadings, and MDLs compatible with GB 50325-2020 requirements for a typical 5 L sampling volume on Tenax TA. While FID-based TD–GC is well suited for routine quantitative surveillance, coupling the approach with mass spectrometric detection would address identification gaps and enhance analytical robustness for complex indoor matrices.

References

1. GB 50325-2020: Code for Indoor Environmental Pollution Control of Civil Building Engineering (Chinese national standard).
2. Chen Shen, Tianming Yao; Shimadzu (China) Co., Ltd. Determination of 16 Volatile Organic Compounds and TVOC in Indoor Air by Thermal Desorption–Gas Chromatography. Application note, First Edition July 2026.