User`s guide

Method Development
226
Figure 65 Glass or Stainless Steel Sample Tubes Containing
Adsorbents of Increasing Strength Linked Together in Series
In this case the light compounds break through the weaker sorbent
and are retained on the stronger one. During desorption, all
compounds exit the tube in the reverse direction, essentially
recombining into an injected band of similar composition to the
original sample. In some cases it is even done to use multiple tubes
in series, with the different tubes containing different packings. This
has the added advantage that when the tubes are dismantled and
stored separately there is no possibility of components migrating
across the sample beds (as there is when using one tube).
Figure 66 Packing a Single Sample Tube with Adsorbents of
Increasing Strength
NOTE: During long-term storage of single tubes packed with more
than one adsorbent, higher boiling components may
migrate from the weak to the stronger adsorbents. This
would cause incomplete desorption during the subsequent
analysis.
Separate tubes can also be useful in identifying the action of each
sorbent, since analysis of each will reveal the distribution of the
compounds across the tubes. In this way it is possible to design a
single tube that has similar properties.
Brass Swagelok Coupling with
One Piece PTFE Ferrules
Tenax
Weak Adsorbent
Medium
Adsorbent
Strong Adsorbent
Sampling
Air Flow
Spherocarb
Chromosorb 102
Charcoal (strong)
Chromosorb 106 (medium)
Glass or Stainless
Steel Tube
Gauze Ring
Glass Wool
Pump
Flow