The amount of gas chemisorbed in a sample is measured by sending pulses of a selected gas onto the sample and measuring its concentration at the reactor exit with the TC cell. In the example shown we see fractional pulses emerging when pulses of 0.5 cc of CO are sent into 45 mg of a 05%Rh/alumina catalyst at room temperature. Subtracting the fractional amounts from the un-adsorbed pulse gives the amount of CO adsorbed. Knowing he amount gas chemisorbed and the amount of catalyst the active area can be estimated.