Submitted by anthias on
Splitless injections are used to transfer all of the injected analytes onto the analytical column for separation and detection and are therefore used for low concentration samples. Opening the split exit too early causes any remaining analytes in the inlet to be flushed out of the split exit and lost. Opening it too late (or not at all) leads to a long, tailing solvent peak which can interfere with the separation and detection of early eluting analytes and provides a higher baseline well into the chromatogram. Opening the split exit at the correct time firstly allows the target analytes to be transferred under splitless conditions and then flushes any remaining solvent trapped around the outside of the liner, preventing it from gradually bleeding onto the column.
How do you determine the split open time? Experimentally, the split open time can be increased stepwise and the analyte responses monitored, a plot of split open time vs. response can be used to determine the point where the response plateaus and the time chosen, although this should not be on the 'cliff edge' for a robust method. A rule of thumb is two flushes of the inlet liner volume and can be quickly calculated as long as the liner volume and column flow are known, transfer will not take longer than this unless the inlet temperature hasn't been optimised, but it could take less time.
To learn more about splitless injections, attend Day 1 of our Complete GC & GC-MS course and Module 3 of our Virtual Classroom Complete GC & GC-MS course.
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