How is column bleed calculated for Zebron capillary GC columns?

Column bleed is measured empirically when every Zebron GC column is QC tested. Every column is installed into the GC instrument and then conditioned. 

At the end of the conditioning step, while the column is still at the elevated conditioning temperature, the signal intensity of the baseline is recorded in picoamps (pA) with the flame ionization detector (FID). The oven temperature is then taken down from the conditioning temperature to the testing temperature, typically 100°C to 140°C depending on the column. At this temperature column bleed is negligible and the resulting signal represents the baseline instrument and detector response.

This baseline signal is recorded at this test temperature. The signal recorded from the lower test temperature is then subtracted from the signal recorded at the conditioning temperature, and the difference is the result of column bleed. This is the value in pA that is reported on every Zebron QC document.