By comparing the measured benzene spectra to one measured with the same spectrometer without using the enrichment, we can determine that the benzene concentration in the enriched samples inside the CEPAS cell was 57 times larger than the benzene con-Figure : Detected benzene concentration from a measurement set with varying benzene levels. The benzene concentration in the sample for the four steps were 2, 1, 0.8 and 0.5 ppb. At the end, the concentration was again set to 2 ppb to demonstrate the repeatability over a measurement period of 4.5 h. In between the steps, the benzene concentration was set to zero. centration in the sample flow. That is, the enrichment offered an enhancement factor of 57. The flow rate into the measurement device was about 0.5 l/min. We estimated before that the effective adsorption period was approximately 30 s. Therefore, we estimate that benzene contained in about 0.25 L volume of sample was captured in one adsorp-tion period. If we further assume that all of this was transported into the CEPAS cell by the gas expanding through the sorbent tube during the desorption step, we can calculate a maximum for the predicted enhancement factor. This assumption would mean that benzene is only moving towards the CEPAS cell with the flow from the volume V d and that all of it escapes the adsorbent, which is clearly an overestimation. The final pressure inside the CEPAS cell was about 440 mbar and the cell volume is about 8 mL. Ignoring the temperature difference of about 20 K, the benzene contained in a gas volume of 0.25 L was effectively measured from a gas volume of 3.52 mL, giving an enhancement factor of 71. This is a rough estimate for the maximum attainable enhancement factor and it is in reasonable agreement with the measurements.