How can I be sure that the cans are clean enough to collect samples?
Method TO-15 describes the protocol to clean them before sample collection; this includes cycles of evacuation & pressurization with a clean air or nitrogen.
After the cleaning process is complete there are two levels of checking that a canister is cleaned to the level needed for the next project.
Batch certification is the routine level to check cleanliness. This entails selecting one canister from the cleaning batch, usually the one that had the highest concentrations, and run a full TO-15 analysis on this canister. If the results of this test come out below routine reporting limits then the whole batch of canisters are certified clean to that level.
Individual certification requires taking each canister to be used for a project and run a TO-15 analysis on each one. This approach is typically used for highly sensitive projects and projects that require lower reporting limits. Note: this method requires more time to prepare the canisters prior to mobilization in the field and also carries extra charges.
Also a consideration is how the canister was manufactured relative to its inner surface. The older SUMMA technology can hold onto compounds making cleaning more difficult. These canisters can “hold onto” compounds effectively lowering the actual concentration. The newer FUSED SILICA inner surface is easier to clean and not as likely to bind compounds.
When preparing for your next air project consider how the canisters were cleaned and work with the lab to pick the right method for your project.