Air monitoring - the respective advantages and applications of canisters and tubes

Importance of the Topic

The monitoring of volatile organic compounds and hazardous air pollutants is essential for assessing air quality, controlling emissions, and protecting public health. Thermal desorption combined with gas chromatography–mass spectrometry provides sensitive analysis across a broad volatility range. The selection between canister and sorbent tube sampling affects analyte retention, stability, and sampling suitability under varying environmental conditions.

Study Objectives and Overview

This note compares canister and sorbent tube sampling methodologies, highlights their respective strengths and limitations, and showcases their complementary use for ambient, workplace, and material emission monitoring. It references international standards and introduces automated cryogen-free TD platforms.

Methodology and Instrumentation

Sampling methods include simple grab sampling using evacuated canisters and time-weighted average monitoring with active or diffusive sorbent tube sampling. Analysis is performed by cryogen-free thermal desorption systems coupled to GC/MS.

Instrumentation Used

• Markes Series 2 (ULTRA-) UNITY-Air Server/CIA TD systems
• Markes UNITY-CIA 8 TD system with splitless analysis
• Gas chromatography–mass spectrometry with a capillary column compliant with US EPA Method 624

Main Results and Discussion

Automated TD platforms achieve desorption efficiencies above 99.95%, enabling rapid reuse of sorbent tubes. Canisters are ideal for ultra-volatile compounds (C2 hydrocarbons, freons) that sorbent tubes cannot retain at ambient temperature. Sorbent tubes excel in sampling semi-volatile and polar analytes (C3 to C30) with minimal artifacts. Practical considerations include the complexity of canister cleaning versus automatic tube conditioning, and the suitability of canisters for grab sampling versus tubes for time-weighted average monitoring.

Benefits and Practical Applications

• Canisters: effective for trace ultra-volatile air toxics in ambient surveys, simple grab sampling, and long-term storage stability
• Sorbent Tubes: versatile for workplace, indoor, ambient, and material emission studies; wide analyte range; personal exposure monitoring; rapid turnaround; cost-effective reuse

Future Trends and Opportunities

Advancements in cryogen-free TD and integrated analytical platforms will further streamline air toxics monitoring. Emerging developments include real-time TD coupling with high-resolution mass spectrometry, expanded multi-sorbent chemistries, and miniature personal samplers for detailed exposure assessment. Standardization of methods for novel indoor and occupational pollutants is anticipated.

Conclusion

Integrating canister and sorbent tube sampling with automated cryogen-free thermal desorption GC/MS offers a comprehensive approach to air toxics monitoring. Strategic method selection based on volatility, concentration, and sampling goals ensures reliable, efficient analysis across environmental and industrial applications.

References

• US EPA Method TO-17: Determination of volatile organic compounds in ambient air using active sampling onto sorbent tubes
• US EPA Method TO-15 and TO-14: Determination of volatile organic compounds in air collected in SUMMA canisters and analyzed by GC/MS
• ASTM D-6196-03: Selection of sorbents, sampling, and thermal desorption analysis procedures for VOCs in air
• ASTM D-5466: Determination of volatile organic chemicals in atmospheres using canister sampling
• ISO EN 16017-1 and -2: Sampling and analysis of VOCs in ambient and workplace air by sorbent tube/TD (pumped and diffusive sampling)
• ISO EN 16000-6: Determination of VOCs in indoor and chamber air by active sampling on Tenax TA, TD, and GC/MS or FID