When using a GC in the split injection mode, up to 99% of the sample is vented to the lab. The Split Vent Trap contains 1200mg of activated charcoal, a highly effective adsorbant, in replaceable tubes. Simply attach the split vent trap to the split vent fitting on your GC, and replace the charcoal tube periodically. The trap comes complete with 3 spare tubes (4 total). 1/8" fittings.