A recently designed Attenuated Total Reflection (ATR)-FTIR flow cell reactor is used to measure the infrared spectrum of molecules adsorbed on carbonate, oxide and clay powders. The reactor is particularly well-suited to measure reaction kinetics as a function of relative humidity [Hashim Ali Ph.D. Dissertation, University of Iowa, 2005]. Experiments done to investigate the uptake of organic acids on carbonate surfaces recently demonstrated the utility of this flow reactor. A commercial ATR horizontal liquid cell apparatus (Pike Technology) was modified for these experiments (see schematic). Approximately 50 mg of the powdered sample (e.g. CaCO₃) is evenly dispersed on an AMTIR element. The top plate of the commercial liquid cell is replaced with a Teflon lid. The Teflon lid contained four openings for a relative humidity sensor, a temperature sensor and the remaining two for the humidified air/organic acid inlet and outlet flows. The commercial air dryer used to purge the FTIR spectrometer is used as the air source. As shown in the flow cell schematics, the humidity of the air was controlled by mixing dry and wet air to reach the desired relative humidity as measured by the RH sensor. The organic vapor pressure was controlled by mixing air saturated with the organic acid vapor with dry air. The two flow streams, humid air and air containing the organic acid, were sent into the modified commercial ATR cell where the reaction was monitored. Data collected for formic acid uptake on CaCO₃ at 33% RH is shown below.