Air Columns - Part II: You only need a 30 m column for EPA Method TO-15!

In part I of this blog series I told you my theory on why most air laboratories are using a 60 m x 0.32 mm x 1.00 µm 1-type column to separate what I refer to as the standard suite of 65 volatile organic compounds (VOCs) for U.S. EPA Method TO-15. I also told you that a 60 m column was not necessary and that I would show you why all you need was a 30 m column…. so here we go. All of the following chromatograms are for 30 m x 0.32 mm x 1.00 µm (1.80 was the closest on the 624 and VMS) columns run with very simple GC programs utilizing close to speed optimized flows (SOFs) (I used 2.0 mL/min for the sake of my MS, not the 2.56 mL/min calculated for a 0.32 mm bore column) and optimal heating rates (OHRs) up to 150 °C.

Take your pick from the following:

 

Rxi-1ms 

 

 

Rxi-624Sil MS 

 

 

Rxi-5ms 

Rxi-5Sil MS 

 

 

and last but not least…

Rtx-VMS 

 

For all of the above chromatograms the coelutions (non-isobaric) were exactly the same as for their 60 m counterpart. With the exception that peak widths were narrower, peak heights were higher (i.e., we increased sensitivity), and GC run times were ~60% shorter for the 30 m column. So why not go even shorter, say 15 m? Well the reason is this… you are only as fast as your slowest process. In the case of air you usually have about a 15 to 20 minute preconcentration period, which just so happens to work out really well with the 30 m column run times. The only reason I would go shorter is for potentially more sensitivity due to increased peak height.

So I have now shown you five 30 m columns with different selectivity’s, which all work very well at separating the standard suite of 65 TO-15 components. Note: elution orders are different for each of the 5 column types, but they all get the job done in their own way. Now if you are like me choices can be troublesome, so which column type do I like the best? Come on… you should know by now that I am going to make you wait for that! Stay tuned for part III, where I tell you my favorite air column and why.