Using the conditions in Table 1, analytical figures of merit for codeine and thebaine for the analysis of aqueous mixed standard solutions of the two analytes were obtained (Table 2).The detection limits for codeine and thebaine were at least an order of magnitude superior to those achieved with other separation methodologies. This enhanced detectability resulted from reduced band broadening and the superior compatibility between the high flow rates through the monolithic column and the kinetics of the chemiluminescent reaction within the detector.