Using gas chromatography to analyse volatile organic compounds in air
Volatile organic compounds (VOCs) are carbon-based chemicals that readily evaporate into the atmosphere. They include benzene, toluene, ethylbenzene, xylenes, solvents, fuel vapours and many compounds released by paints, adhesives, cleaning products and industrial processes. Measuring these substances helps scientists investigate odours, workplace exposure, indoor air quality and pollution near roads or industrial areas.
Gas chromatography (GC) separates VOCs so they can be identified and measured individually. In Australia, the technique is useful for studies ranging from bushfire smoke and urban air in Sydney or Melbourne to emissions near mining, petroleum and manufacturing sites in Western Australia and Queensland. With careful sampling and quality control, a small air sample can provide detailed information about chemical exposure.
How gas chromatography separates air pollutants
A gas chromatograph first receives a prepared air sample. The sample is vaporised and carried through a long capillary column by an inert gas such as helium or hydrogen. Different VOC molecules interact with the column’s stationary phase to different extents, so they leave the column at different times. These arrival times are called retention times.
A detector records the compounds as peaks in a chromatogram. Peak area is related to the amount of a substance, while the retention time helps identify it. A flame ionisation detector (GC-FID) is widely used for hydrocarbons because it provides a strong response to many organic compounds. A mass spectrometer (GC-MS) gives more specific identification by producing a characteristic mass spectrum for each compound.
The choice between GC-FID and GC-MS depends on the purpose of the investigation. GC-FID can be reliable and cost-effective for a known group of hydrocarbons, whereas GC-MS is valuable when the sample may contain unfamiliar chemicals or when confirmation is important.
Collecting representative air samples
Air sampling must happen before the instrument can produce meaningful results. Sorbent tubes packed with materials such as activated charcoal or Tenax are commonly used. A calibrated pump draws a known volume of air through the tube, where VOCs are retained. In the laboratory, the compounds may be removed by solvent extraction or thermal desorption before entering the gas chromatograph.
Sampling time and flow rate should match the expected concentration. A short, high-flow sample may capture a brief emission event, while a longer sample can describe average exposure during a work shift. Field blanks, duplicate samples and transport blanks help reveal contamination from handling, storage or the sampling equipment itself.
Australian conditions require practical planning. High summer temperatures can affect sample stability, and long transport distances may matter when samples travel from regional Queensland or the Northern Territory to a laboratory in Brisbane, Perth or Melbourne. Sampling teams should use clean containers, cool storage where required and documented chain-of-custody procedures.
Choosing the method for the investigation
The instrument and sampling approach should reflect the question being asked. A workplace hygienist measuring solvent exposure may need personal sampling near a spray-painting task. An environmental scientist investigating petrol vapours may use fixed-point monitoring near a service station, while a researcher studying indoor air may compare classrooms, homes and laboratories.
| Approach | Strengths | Typical use | Main limitation |
|---|---|---|---|
| GC-FID | Robust, sensitive to hydrocarbons, relatively economical | Routine measurement of known solvents and fuel-related VOCs | Limited chemical identification |
| GC-MS | Strong compound identification and confirmation | Complex environmental samples and unknown VOCs | Higher cost and greater instrument complexity |
| Sorbent tube with thermal desorption | Low solvent background and good sensitivity | Workplace and ambient air monitoring | Requires specialised desorption equipment |
| Canister sampling | Captures a broad range of VOCs for later analysis | Ambient air surveys and short-term investigations | Canisters need careful cleaning and quality control |
| Direct injection or online GC | Rapid or near-real-time results | Process monitoring and research applications | Less suitable for all field conditions |
Target compounds should be selected before analysis wherever possible. Benzene may be important near fuel handling, while formaldehyde and other oxygenated VOCs may matter indoors. A certified reference material, calibration standards and a method detection limit are needed to connect chromatogram peaks with defensible concentrations.
Interpreting results safely and accurately
A chromatogram is not automatically a complete description of air quality. Co-elution can occur when two compounds leave the column at nearly the same time, producing overlapping peaks. Background contamination may come from solvents, tubing, laboratory air or instrument components. Analysts therefore use retention-time checks, internal standards, calibration verification and, where necessary, a second column or mass-spectral confirmation.
Results are usually reported as parts per billion by volume, micrograms per cubic metre or milligrams per cubic metre. Converting between units requires the compound’s molecular mass, the sampling temperature and pressure. The report should also state the sampled air volume, sampling duration, analytical method, uncertainty and any dilution or recovery correction.
For Australian workplace studies, results may be assessed against guidance from Safe Work Australia and relevant workplace exposure standards. Ambient investigations may involve state or territory environmental authorities and the National Environment Protection framework. A NATA-accredited laboratory can provide additional confidence when results may support regulatory decisions, occupational health actions or community investigations.
From chromatogram to useful evidence
GC data become more useful when combined with location, time and activity records. A spike in toluene near a workshop might correspond to solvent use, while a pattern of benzene, toluene and xylenes may suggest fuel-related emissions. Comparing indoor and outdoor samples can help distinguish building materials from traffic or industrial sources.
Community projects also benefit from clear communication. Nepali chemistry students and researchers working in Australia can use VOC analysis to connect analytical chemistry with public health, environmental justice and occupational safety. A university laboratory in Melbourne, a regional council near Newcastle or an industrial site in Perth may have different sampling constraints, yet the same principles of calibration, blank control and transparent reporting apply.
A sound project begins with a written sampling plan: define the compounds, choose the collection device, record the air volume and preserve the samples correctly. The practical next step is to select one target VOC, prepare a calibration series with a certified standard, and analyse a field blank alongside the first air sample.