Using High Performance Liquid Chromatography (HPLC):
The chromatograms below are simulated with Gaussians using the actual times and peak areas from the original data compiled by Dr. Robert Williams on 4/28/97. The column was a Versapack C18 10 micron 300 mm x 4.1 mm Alltech #28034 . The flow rate was 2.00 mL/minute using an ISCO Model 2350 Pump. The sample loop was 10 microliters. The ISCO V4 Variable Wavelength Detector was set to 254 nm.
"Water" is actually 1.5%(v/v) acetic acid in water. The peaks are acetaminophen, caffeine, aspirin, and salicylic acid -- in that order once they are resolved. An Excedrin tablet was dissolved in 30 mL of Methanol. The tablet composition was stated to be 250 mg Acetaminophen, 250 mg Aspirin, and 65 mg Caffeine. 150 mg of Salicylic Acid in 10 mL of Methanol was added as an internal standard. In the first few chromatograms, only the salicylic acid is resolved as a separate peak. An impurity peak that appeared near the salicylic acid in the last two runs is not shown.
David L. Zellmer, Ph.D.This page was last updated on 1 May 1997
Department of Chemistry
California State University, Fresno