US EPA Method TO 15 Volatile Organic Compounds in Ambient Air

Significance of the Topic

Volatile organic compounds (VOCs) in ambient air originate from industrial, mobile and waste sources and pose risks to human health, ecosystems and climate. Regulatory bodies worldwide mandate monitoring of VOCs at trace levels. The US EPA Method TO-15 provides a standardized approach for quantifying a broad suite of toxic organics in air, addressing analytical challenges posed by low concentrations and diverse chemical properties.

Objectives and Scope of the Study

This application note evaluates the SCION TO-15 analyser for compliance with US EPA TO-15. Key aims include demonstrating reliable sampling, preconcentration, chromatographic separation and mass spectrometric detection of over 60 VOCs. The study focuses on calibration linearity, detection limits, dynamic range and method robustness.

Methodology and Instrumentation

Samples were collected in evacuated canisters treated with water to deactivate internal surfaces. A mass flow controller (50 mL/min) loaded 300 mL of sample onto a hydrophobic mixed-bed adsorbent trap. Moisture and light gases were vented before thermal desorption. The SCION TO-15 analyser comprises:

• SCION 456 GC with built-in sample preconcentration trap (SPT)
• Single-quadrupole MS featuring an Extended Dynamic Range Detector (EDR)
• SCION-1MS column (30 m × 0.32 mm × 1.0 µm)
• Adsorbent trap temperature program: 55 °C (9.1 min), ramp at 200 °C/min to 202 °C (51.3 min)
• Oven program: 50 °C hold, –100 °C/min to 0 °C, 5 °C/min to 50 °C, 8 °C/min to 150 °C, 25 °C/min to 220 °C
• Carrier gas: constant 2 mL/min
• MS transfer line: 170 °C, ion source: 200 °C, SIM mode

Calibration standards ranged from 0.01 to 100 nmol/mol via serial dilution of a 1 µmol/mol mix. Internal standards (bromochloromethane, chlorobenzene-d5, 1,4-difluorobenzene) were spiked directly onto the trap.

Main Results and Discussion

A 100 ppb(v/v) calibration mix produced well-resolved chromatograms for all target analytes. Toluene, representative of common tropospheric VOCs, exhibited a correlation coefficient (R2) of 0.999 over a >100 000-fold concentration range. Relative response factors (RRFs) remained within EPA TO-15 criteria (<30% RSD across most levels; <40% for up to two points), confirming system linearity over >300 000-fold dynamic range. Detection limits for selected compounds ranged from 0.004 to 0.013 µmol/mol using only a 300 mL sample.

Practical Benefits and Applications

By integrating a high-efficiency preconcentration trap with EDR mass spectrometry, the SCION TO-15 analyser enables:

• Accurate quantification of VOCs from fmol/mol to nmol/mol without instrument reconfiguration
• Reduced analysis time and elimination of repeat runs
• Robust ambient air monitoring for environmental, industrial and regulatory applications

Future Trends and Potential Applications

Advancements may include real-time field deployable analysers, expanded compound libraries (e.g., emerging pollutants), and integration with IoT networks for continuous monitoring. Machine learning algorithms could further enhance calibration, data processing and predictive emission modeling.

Conclusion

The SCION TO-15 analyser meets US EPA TO-15 requirements by delivering exceptional sensitivity, wide dynamic range and streamlined sampling. Its combination of preconcentration, extended dynamic range detection and automated analysis simplifies VOC monitoring in ambient air, supporting regulatory compliance and environmental research.

References

1. Bramston-Cook R. Air Scion Brochure. Lotus Consulting, Long Beach, CA; 2018. pp.1-8.