Abstract
Aspirin, phenacetin, and caffeine in two commercial analgesic tablets were determined by scanning of fluorescence-quenched zones after separation on high performance TLC plates. Assays for the components ranged from 100 to 88% of label values, and agreement between duplicate samples was better than 5%. Use of phenacetin as an internal standard for determination of aspirin and caffeine was not advantageous. The analysis serves well as an introduction to quantitative TLC in undergraduate laboratory courses.