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 \u201cdirt\u201d 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\u2019s slow.<\/p>\n\n\n\n
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.\u00a0 This range provides a buffer for quantitative transfer as the liner\/seal gets dirty and analytes have to \u201cchromatograph\u201d 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.\u00a0 We provide an easy way to calculate splitless valve time through our new\u00a0EZ<\/em>GC\u00a0<\/sup>Method Translator and Flow Calculator<\/a>\u00a0(MTFC).<\/p>\n\n\n\n Using the Flow Calculator:<\/p>\n\n\n\n I\u2019ve outlined the steps graphically below. <\/p>\n\n\n\n