How should I condition a TD tube?
Before TD tubes can be used the desorption tubes must be conditioned. Conditioning involves the continuous flow of a high purity carrier gas (either Nitrogen or Helium) while the desorption tubes are heated at elevated temperatures. Set a flow rate of 10 to 50 ml/min and allow to purge for about 5 minutes to remove all traces of oxygen from the adsorbent resin inside the desorption tube.
Begin to heat the desorption tube while continuing to purge gas through the adsorbent resin inside. We recommend a temperature program of 1°/sec from 45°C up to the maximum temperature required for conditioning. After the desorption tube reaches the maximum temperature, continue the conditioning process for 2 to 4 hours. Temperature should be maintained at the upper limit during this time phase and continuous flow must be maintained through the desorption tube and resin at all times. This can be done in the OPTIC inlet or some external device.
The selection of the upper temperature limit is a function of both the adsorbent resin and the temperatures at which it will be thermally desorbed when the samples are analysed. In no case should the conditioning temperature exceed the maximum rated temperature for the adsorbent resin. If possible the desorption tube should be conditioned 25° higher than the temperature at which it will be desorbed. The higher the temperatures at which you condition, the lower the life of the resin. For example Tenax TA has a maximum temperature of 350°C.
However many applications typically desorb samples at temperatures between 200 and 280°C. Therefore condition the tubes over 300°C is not needed. Desorption tubes can be used about 100 times. Good practise is to replace the trapping material on time or just replace the TD tube.
After the heating cycle time is complete, the desorption tubes should be cooled to room temperature and removed. Gas flow must be maintained through the adsorbent resin during the cooling cycle. Do not purge with carrier gas any longer than necessary, since any volatiles in the carrier gas (even though present in less than ppb levels) will be trapped on the resin which is now at room temperature. Cap the TD tubes on both sides for storing them.
Theoretically, the conditioned desorption tubes can be stored several weeks before use. But whenever possible it is always best to use fresh tubes.