A high-pressure, high-temperature apparatus has been developed for the analysis of sorbents capable of removing alkali compounds to the concentration levels required by advanced, coal-fired power generating systems. The reactor is capable of operating at temperatures up to1200 °Cand pressures up to 2.0 MPa. A laser-based technique—photofragment fluorescence—enablesin situanalysis of the sodium content in a gas stream before and after a sorbent bed thereby determining the efficiency of the alkali removal by the various sorbents studied (typically alumino-silicate clays). The design and development of both the reactor and the laser-based analytical technique is described. ©1998 American Institute of Physics.