A wide range of stimulants was rapidly and efficiently separated with symmetrical peak shapes with a tertiary supercritical mobile phase and a cyanopropyl liquid chromatography column. Compared with other drug families studied in this series, the stimulants exhibited a much broader range of retention. Several strong bases, including primary aliphatic amines, were easily eluted with a modified mobile phase. The stimulants were generally more retained than antipsychotic drugs. Compared with antidepressant drugs, a few stimulants behaved similarly, but most were more strongly retained. Modifier concentration proved to be the most effective means for changing both retention and selectivity. An over-the-counter eye drop solution (an aqueous buffer) was analyzed for tetrahydrozoline. The positive results with good peak shapes indicate that packed-column supercritical fluid chromatography is compatible with at least small aqueous samples.
