There are a lot of samples (food, environmental for US,environmental forEU, drugs of abuse, forensic, or any other type) to analyze. That means there are a lot of samples to extract and run on the Gas Chromatograph. We would like to spend as little time as possible on the sample preparation. However, without sample cleanup the potential to contaminate the GC column and potentially the mass spectrometer source, if that is the detector. The time that is saved in sample prep could be wasted in maintenance. That is where backflush comes in. Backflush on the PTV injector provides the means to remove the high boiling point contamination that will contaminate the column, and the rest of the system, that is missed during a fast sample preparation.
The backflush technique on the Trace GC Ultra keeps the contamination away from the analytical column; it does not require that the sample go all the way through the column and then back through the column, which would contaminate it twice. The PTV injection technique shows significant advantages over conventional hot split-splitless or on-column injection. First, by avoiding evaporation from the syringe needle, it eliminates an important source of discrimination of high boiling components. Additionally, non-volatile sample by-products are retained in the injector insert liner. Finally, in the solvent split mode the PTV allows splitless injection, even of larger sample volumes than only 1 or 2 uL, with a minimum transfer of solvent to the column and to the detection system. The PTV can also use carrier gas backflush of the heavier components of the extract when they are not of interest, preventing their entrance in the analytical column. This greatly increases the robustness of the whole chromatographic system for routine applications.
Development of a backflush method follows five simple steps
Make sure the backflush mode is deactivated.
Inject a standard with the optimized oven temperature program required for the complete elution of all of the compounds of interest.
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Turn on the backflush and set a long time, use the elution time of the last component of interest. Set a long cleaning time and about 50 mL/min flow for the cleaning.
Inject a standard sample and compare it to the injection in step 2.
Adjust the time for the backflush to ensure the last peak is present and not diminished. This will be the correct backflush time.
Page 5 of the application note, download below, demonstrates the use of the PTV backflush technique on the Trace GC Ultra in a sample.
Download Application note here; PTV with backflush