Air Columns - Part 1: Why use a 60 m column for EPA Method TO-15?

Yes, the title of this blog is a question, because I have always wondered why a lot of air laboratories are using 60 m columns for U.S. EPA Method TO-15!?!?!? From everything I have seen, most laboratories are only analyzing what I refer to as the standard suite of 65 volatile organic compounds (VOCs) for TO-15. Now to be fair, Method TO-15 is applicable to a subset of 97 VOCs that are from the list of 189 hazardous air pollutants (HAPs) included in Title III of the Clean Air Act Amendments, but only a few laboratories are analyzing all 97 components. Some researchers add in an additional dozen or so compounds (on top of the 65 that is), but again for the most part everyone is looking at approximately the same 65 analytes. Not exactly an exhaustive list, so it should not require a 60 m column in my opinion. But why then are so many air labs using 60 m columns!?!?

65 TO-15 Components + ISTDs on a 60 m x 0.32 mm x 1.00 µm Rxi-1ms

Welllll… I do have a theory on why. See back in the day… Rasmussen (one of the godfathers of whole-air canister-based sampling and analysis) conducted an extensive amount of research on hydrocarbons. At the time he did so with a 60 m x 0.32 mm x 1.00 µm 1-type column because his detector was an FID and everything was based on retention time. As years went on subsequent researchers copied Rasmussen and therefore used a 60 m x 0.32 mm x 1.00 µm 1-type column. Makes sense… right???

Well yes and no… see it made sense “back in the day”, but somewhere along the line the air community failed to advance their column selection with the adoption of mass spectrometers for air analysis. This is the part that leaves me perplexed!!!

Unfortunately, while working for the U.S. EPA I was not afforded the luxury of experimenting with different GC columns. So I too used to be one of the many using a 60 m x 0.32 mm x 1.00 µm 1-type column. Obviously once I joined Restek I got to play around with other columns. The first order of business for me was to see how 30 m columns performed from TO-15 analyses. Now that we understand a little bit of the history behind TO-15 columns… stayed tuned to part II of this series where I demonstrate that all you need is a 30 m column for the standard suite of 65 TO-15 compounds!!!