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US EPA Method TO-15 defines performance criteria for the sampling and analysis of volatile compounds in air contained in canisters, and is primarily employed for the monitoring of airborne pollutants in urban and industrial environments.

What does Method TO-15 involve?

Method TO-15, which is the successor to Method TO-14A, is a ‘performance-based’ method for the analysis of subsets of the 97 hazardous pollutants listed in the 1990 Clean Air Act Amendments. It does not offer detailed method guidance, but instead defines criteria for acceptability of performance, and as a result, many of the experimental aspects are described only in the broadest terms.

However, a typical procedure involves drawing the sample atmosphere into an evacuated canister (usually 1 L or 6 L in volume). The canister is then transported to the laboratory, where the sample is preconcentrated onto a focusing trap within a thermal desorber, followed by GC–MS analysis.

Samples taken for analysis in accordance with Method TO-15 are often from humid environments, and this is a point that requires careful consideration, as existing methods such as Nafion dryers can cause loss of certain ultra-volatiles.

Lowering limit levels – What is Method TO-15A?

Increasingly, analysts are finding that the criteria in Method TO-15 are not stringent enough to address the requirement to detect ever-lower levels of analyte concentrations in ambient air.

Therefore, there have been moves in the USA to develop ‘low-level’ TO-15 methods, amongst which the New Jersey method (NJDEP LL TO-15) is an early example. Work on a revised edition of TO-15 itself, to be called TO-15A, is currently ongoing. However, it is likely to include more stringent requirements on canister cleanliness, method detection limits, sample validity and mass spectrometer tuning.

Complying with Method TO-15 now and in the future

Achieving the ppt-level detection limits required by evolving TO-15 methods, combined with sampling VOCs from humid environments, can make compliance a daunting prospect.

However, Markes’ UNITY–CIA Advantage-xr canister preconcentration systems comply fully with the requirements of TO-15 and low-level methods such as NJDEP LL TO-15. A particular feature of our systems is the incorporation of the Kori-xr water condenser module, which eliminates the analyte loss associated with other water management approaches.

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