Determination of Acetaminophen in Analgesics by the Standard Addition Method: A Quantitative Analytical Chemistry Laboratory


Chemistry and Biochemistry

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The ability of the standard addition method to correct for interference was evaluated by analyzing Tylenol and Migraine tablets for acetaminophen. These formulations are ideal for standard addition method study because they provide varying degrees of interference. For Tylenol tablets, the spectrum of diphenhydramine interferes with that of acetaminophen around 200 to 235 nm while there is minimum interference between 235 to 260 nm. In Migraine tablets (acetaminophen, aspirin, caffeine), all the active ingredients overlap strongly with the spectrum of acetaminophen. The two extremes provide a basis for observing the performance of the standard addition method versus the external standard method. A BioCary100 UV/Vis spectrophotometer was used to obtain absorbance spectra of tablets dissolved in 20% aqueous ethanol in the 200 to 310 nm range. A Dionex high-performance liquid chromatograph (HPLC/UV) was used to provide reference results. For Tylenol analysis, the standard addition method gave 2.6% relative error under conditions where the external standard method gave 10% relative error for acetaminophen. With the Migraine analysis, no suitable analytical window could be found, and the results were statistically unsatisfactory.