The Solvent Effect in Concurrent Solvent Recondensation Large Volume Splitless Injection with Methylene Chloride – EPA Method 8270 Semivolatiles

Michelle Misselwitz and I are again exploring large volume splitless injection with an off-the-shelf, unmodified Agilent splitless injector, continuing the work we recently presented at Dioxin 2010 and in some seminars in Canada during January.  We often get asked from environmental chemists if this technique will work with methylene chloride solvent, specifically for EPA Method 8270, Semivolatile Compounds by GC-MS.  It will!

We are using a Restek Premium Inlet Liner (single taper with wool, cat.# 23303) in an Agilent GC splitless inlet, and a 5m x 0.53mm IP Deact retention gap (cat.# 10045) press-fit (cat.# 20429) to a 30m x 0.25mm x 0.25µm Rxi-5Sil MS  GC column (cat.# 13623).  We make fast injections with an Agilent 7673/7683 type autosampler and achieve excellent chromatographic results for the compounds in the 8270 MegaMix (cat.# 31850).

In traditional splitless injection, to achieve good peak shapes for early eluting compounds, we use the “solvent effect”, where starting the GC oven temperature anywhere from 10-40°C below the boiling point of the solvent creates a temporary, thick “stationary phase” of solvent to focus more volatile components.  This prevents tailing peak shapes.  Without cryogenic cooling, this really can’t be done with methylene chloride since its boiling point is around 39-40°C.  But we’ve discovered what may be a previously unknown benefit of concurrent solvent recondensation large volume splitless injection, and that is the ability to start the GC oven temperature higher than the boiling point of the solvent.  Check out the chromatograms below (first eluting peaks) for a 5µL x 1 ng/µL 8270 MegaMix-in-methylene chloride splitless injection on a 55°C GC oven start.  Not bad, eh?

For those quick thinkers in the audience, hopefully you’ve already jumped ahead to seeing immediate benefits for this approach.  It takes longer to cool a GC oven to 30 or 40°C without a cryogenic liquid (labs rarely use cryogenic cooling for 8270 GC-MS), so starting at 55°C will increase sample throughput.  And (a big AND), you can stop your extract evaporations short and just inject more sample.  This decreases sample preparation time and increases recoveries for volatile analytes (we’ll prove this to you in an upcoming blog and work to be shown at PittCon 2011 in Atlanta, Dioxin 2011 in Belgium, and several other conferences).

P.S.  Do you know why the large volume splitless injection allows good peak shape at higher GC oven starting temperatures?

Large volume splitless injection of EPA Method 8270 semivolatiles in methylene chloride at a starting GC oven temperature of 55°C. The very early eluting compounds NDMA and Pyridine are shown here.

Large volume splitless injection of EPA Method 8270 semivolatiles in methylene chloride at a starting GC oven temperature of 55°C. Early eluting compounds are shown.