Conditioning GC-H (high temperature)

To prevent interaction of the sample with the ceramic furnace tube, a layer of carbon is required on the inner surface of the tube; this can achieved by ‘conditioning’.

Conditioning the furnace tube with hexane

The following protocol conditions the ceramic furnace tube by injection of hexane with a split / splitless injector. The process involves vaporizing the hexane and allowing it to pass through the furnace tube at 1450°C where it will deposit its carbon on the inside wall.

  1. Ensure that the system is leak free
  2. Configure the split / splitless injector into split mode with an operating temperature greater than 200°C
  3. Set the furnace with an operating temperature of 1450°C
  4. Close the heart split valve using lyticOS (i.e. diverts the GC column flow through the furnace tube).
  5. Isolate the ion source by

  1. Closing the isolation valve

    and/or

  1. Changing the source inlet valve to ‘All off’
  1. Set the GC oven temperature to 100°C (i.e. higher than the boiling point of hexane and thus prevents focusing on the front of the GC column)
  2. Inject 1-2ul of hexane into the injector with split ratio of approximately 5.0
  3. Repeat step 7) 3 or 4 times every 3 minutes

Please note that the above protocol used a standard 4mm injector liner (e.g. vol. approx. 1000ul). If a smaller liner is used then please be aware of backflash in the injector and adjust your injection volume accordingly.

The method can be adjusted for systems with different injectors, e.g. cold on column (COC) or programmable temperature vaporization (PTV). As you cannot split injections in a COC injector, it is necessary to inject smaller volumes of hexane so not to overload the reactor (<0.5ul). Smaller injection volumes are also required when using a PTV injector as their injection liners typically have a very small volume, typically ~100ul; please ensure that the vapour volume of the hexane does not exceed the volume of the liner.

A variety of GC columns can be used in the conditioning process, however it is not recommended to use the HP-PLOT/Q column, as supplied with the EnvirovisION System, due to the long retention time for hexane. Instead injection of a gas such as methane is preferred.

Conditioning the furnace tube with methane

An alternative to conditioning with hexane is to inject methane gas.

This protocol follows the same approach as hexane conditioning, except the injector is normally setup in splitless mode and as methane is already in the gas phase a larger volume is injected.

  1. Ensure that the system is leak free
  2. Configure the split / splitless injector into splitless mode, temperature is not critical.
  3. Set the furnace with an operating temperature of 1450°C
  4. Close the heart split valve using lyticOS (i.e. diverts the GC column flow through the furnace tube).
  5. Isolate the ion source by

  1. Closing the isolation valve

    and/or

  1. Changing the source inlet valve to ‘All off’
  1. Set the GC oven to a temperature that allows methane to elute of the column
  2. Inject 100ul of methane into the injector with a gas tight syringe
  3. Repeat step 7) 4 or 5 times every 3 minutes