The Determination of Vehicle Emissions in Exhaust Gases and Ozone Precursors in Ambient Air with a Built-in Preconcentrator/GC System

Importance of the topic

This study addresses the analysis of hydrocarbons emitted by internal combustion engines and their role as ozone precursors. Precise quantification of C2–C13 compounds is essential for understanding and controlling photochemical smog formation. Analytical methods capable of handling the wide concentration range between tailpipe and ambient levels are crucial for regulatory compliance and air quality management.

Objectives and overview

The main goals of the application note are:

• To demonstrate the performance of a custom GC system with built-in preconcentrator and dual flame ionisation detectors.
• To validate the system’s precision and recovery for target hydrocarbons (C2–C13).
• To highlight its suitability for both exhaust and ambient air monitoring.

Methodology and instrumentation

Sample introduction and pre-concentration:

• 100 mL sample drawn through a nafion dryer into a multi-adsorbent trap (Tenax/Carbotrap/Carbosieve) at 0 °C.
• Trap purge for 1 min to remove residual air, followed by backflush desorption at 220 °C.

Chromatographic separation:

• Dual capillary columns (split effluent stream):
• Column 1: PLOT Al₂O₃/KCl, 50 m × 0.32 mm × 5 µm, flow 2.5 mL/min for C2–C6 separation.
• Column 2: SCION-1, 60 m × 0.32 mm × 1 µm, flow 3.2 mL/min for C6–C13 separation.
• Oven program: hold at 0 °C for 10 min, ramp 10 °C/min to 200 °C.

Detection:

• Dual FID configuration to record two chromatograms simultaneously (C2–C6 and C6–C13).

Main results and discussion

Chromatographic performance and precision:

• Retention time RSDs below 0.08% across C6–C12.
• Peak area RSDs below 1.4% even for higher-boiling analytes.

Recovery evaluation:

• Excellent recoveries up to C11 (100% for C6–C9, 97% for C10, 86% for C11).
• Recovery decrease noted for C12 (~50%), indicating adsorption challenges for heavier hydrocarbons.

The system reliably separates and quantifies both saturated and unsaturated hydrocarbons, supporting EPA requirements for ozone precursor analysis. Unidentified components may require coupling to mass spectrometry for confirmation.

Benefits and practical applications

The custom GC with built-in preconcentrator and dual FIDs offers:

• High sensitivity across a broad concentration range.
• Robust precision suitable for regulatory monitoring of vehicle emissions and ambient air.
• Fast sample throughput with integrated drying and trapping.

Applicable in automotive emissions testing, urban air quality assessment, and industrial process monitoring.

Future trends and potential uses

Advancements may include:

• Integration with mass spectrometry for compound identification of unknowns.
• Enhanced adsorbent materials to improve high-boiling compound recovery.
• Automated field deployable units for real-time monitoring of urban ozone precursors.

Conclusion

The described SCION GC system with preconcentrator and dual-column/FID setup delivers precise, high-recovery analysis of C2–C13 hydrocarbons. Its capability to handle both high and low concentration samples makes it a versatile tool for emissions and ambient air studies, fulfilling stringent regulatory requirements.

Reference

• SCION Instruments. The Determination of Vehicle Emissions in Exhaust Gases and Ozone Precursors in Ambient Air with a Built-in Preconcentrator/GC System. Application Note. SCION Instruments NL BV4462GN, Goes, Netherlands; SCION Instruments HQ, Livingston Business Centre, West Lothian, UK.