Split Injection Makes for Easier Polar Solvent GC Work versus Splitless Injection

As anyone who’s doing QuEChERS knows, analyzing acetonitrile extracts on nonpolar GC columns (like Rxi-5ms, e.g.) using splitless injection can be problematic because of the classic solvent – stationary phase mismatch.  To avoid split peaks we usually have an initial GC oven temperature slightly above the 82°C boiling point of acetonitrile (MeCN), but this causes tailing of early eluting peaks as they are not focused using the “solvent effect” or cold trapping.  Life is much easier if we can do split injection at, say, a ratio of 10:1, since instead of, e.g., 1 microliter, we now have approx. 0.1 microliter of polar solvent going onto our nonpolar GC column.  Of course you need to pay attention to the hit on your LODs and LOQs, but with more sensitive MS/MS instruments being developed every year, split injection for pesticide residue work is becoming practical.  Given that approx 10 times less extract goes onto the column and into the MS source, system uptime is greatly improved, too.  A Restek Premium Precision split liner with wool and “shoot-and-dilute” GC (split injection GC) makes life easier!

Split MeCN

One Response to “Split Injection Makes for Easier Polar Solvent GC Work versus Splitless Injection”

  1. That certainly is an improvement, Jack, and split injection is always preferred if in GC if detection limits permit. We’re going to give split injection a try on our state-of-the-art GC-MS/MS, but we need an LOQ at least 4-fold lower than what you show for methamidophos (I estimated S/N = 50 in the split example). I would also like to point out a few things (that you already know, but your readers might not): 1) all 3 pesticides shown can be analyzed by LC-MS/MS, often better than GC; 2) in GC, their peak shapes (and sensitivity, precision, and robustness) are much improved by using analyte protectants; 3) use of programmable temperature vaporization (PTV) allows large volume injection (LVI) of MeCN and reduces the problem shown in the upper chromatogram; and 4) fast-low pressure GC-MS(/MS) with a thicker stationary phase handles larger amounts of MeCN while also speeding analysis (<10 min chromatograms for the full suite of pesticides), enhancing sensitivity (taller peaks), and providing much greater ruggedness with a small loss of separation efficiency. We've successfully been using PTV-LVI and analyte protectants in fast, low-pressure GC-MS(/MS) since we developed QuEChERS in 2002. I strongly suggest for your readers who don't have state-of-the-art GC-MS/MS instruments to read our numerous publications about it and give it a try!

Leave a Reply