Meaning
Environmental investigations and vapor intrusion studies require reliable methods for collecting air samples to analyze volatile organic compounds. The process of summa canister sampling utilizes a stainless steel sphere with an electropolished internal surface to collect and store whole air samples for subsequent analysis. This specialized surface treatment prevents the volatile compounds from adhering to the walls of the container, ensuring that the collected sample remains representative of the ambient air.
The canister is prepared by pulling a high vacuum, which later draws the air sample into the vessel when the valve is opened.
Sample Collection
Gathering air samples must be done with precise flow control to ensure a representative mixture. During summa canister sampling, a flow controller is attached to the inlet valve to regulate the rate of air intake over a specified period. This setup allows for either a grab sample or an integrated sample collected over several hours.
The operator records the initial and final vacuum levels to verify that the canister has filled correctly.
Quality Assurance
Verifying the cleanliness of the sampling equipment is necessary to avoid cross-contamination. Before a canister is sent to the field, the laboratory performs a multi-step cleaning process that involves heating and purging with high-purity nitrogen. A portion of the cleaned canisters is then tested to confirm that no residual volatile compounds remain.
This quality control step ensures that any detected compounds originate solely from the sampling site. The laboratory documents these cleaning cycles and maintains a certificate of cleanliness for each canister to provide a defensible chain of custody for regulatory compliance.
Laboratory Analysis
Analyzing the collected air sample involves sophisticated laboratory equipment. Once the canister returns to the laboratory, the air is analyzed using gas chromatography. This method can detect and quantify volatile organic compounds at very low concentrations.
