Calculating Splitless Valve Time for Splitless Injection GC with the New EZGC Method Translator and Flow Calculator - Pesticides

Properly setting the splitless valve time (SVT) for splitless injection in gas chromatography (GC) is probably one of the most overlooked optimization parameters for pesticide analysis today.  Having too short of a SVT leads to poor transfer of active and involatile pesticides, especially as the liner becomes contaminated with “dirt” from injected sample extracts.  This leads to poor quantitative results and possibly the premature need to recalibrate the GC.  The reason a proper SVT is so important has to do with the long sample transfer time from the inlet to the GC column inherent in splitless injection.  In general, the flow through the inlet is in the same order-of-magnitude as the capillary GC column outlet flow, which means it’s slow.

A rule-of-thumb for setting the SVT (sometimes known too as purge valve time) is to sweep the inlet liner completely with carrier gas 1.5 to 2 times before opening the split valve.  This range provides a buffer for quantitative transfer as the liner/seal gets dirty and analytes have to “chromatograph” out of the dirt to get to the column, while keeping the transfer time short enough to avoid a long solvent tail that might obscure earlier eluting analytes.  We provide an easy way to calculate splitless valve time through our new EZGC Method Translator and Flow Calculator (MTFC).

Using the Flow Calculator:

• Enter your Column length, inner diameter, film thickness, and starting oven temperature.
• Enter your Column outlet flow, and click “Atm” or “Vacuum” depending on whether you’re using an ambient pressure (Atm) detector like ECD, or a vacuum-outlet detector like a mass spectrometer (MS).
• Enter your inlet temperature and your inlet liner volume (this can be calculated or if you’re using an HP or Agilent GC inlet liner, you can find liner volumes in the MTFC Glossary).
• The Splitless Valve Time range that should be used is calculated automatically.

I’ve outlined the steps graphically below.  For additional reading, try this ChromaBLOGraphy post:

Setting the splitless injection purge valve time in gas chromatography