QualitativeAnalysis of Analgesic Tablets An Experiment Employing High Pressure Liquid Chromatography Rodney W. Beaver, John E. Bunch, and Louis A. Jones North Carolina State University. Raleigh, NC 27650 T h e role of high pressure liquid chromatography (HPLC) in analytical chemistry is rapidly expanding. However, due to the very high cost of HPLC instrumentation, undergraduates are seldom introduced to the technique via practical, "hands on" exoeriments. For exam~le. . . a t this Universitv... chemistry majors receive no instrurt~onin HP1.C save for a brief l e ~ t u r ein the senior-lwel analvtical coura.. We soueht to develop an experiment which woild allow the studentiin the iunior-level aualitative oreanic analvsis course to actuallv "do:' H PLC, huiwhich would require the use of our research HPLC instruments for a minimum amount of time. The experiment developed involves the qualitative assay of several over-the-counter (OTC) analgesic tablets. T h e student is providrd with sweral standards (acetominophrn (I). caffeine (11). salicvlamide (Ill), acetvl salirvl;~te(IV),and phenacetin (v)-see eig. 1for stru&uresj which are commonly found either singlv or in various combinations in several common OTC &aigesic tablets. T h e student then develops a chromatogra~hic - - system capable of resolving all five standards. Acetominophen (I)and acetyl salicylate (2)have been determined using normal phase HPLC on Silica-Gel columns. However, we preferred to utilize a reversed-phase system employing an octadecylsilane (C-18) column and chose to use a system similar to the one reported by Williams e t el. (3)for the determination of caffeine, acetyl salicylate, salicylic acid, and phenacetin. A reversed-phase (RP) commerical C-18 column was provided, and the students were instructed to develop the separation usine mobile ~ h a s e cs o m ~ o s e dof varvine . ...Dercentaees of methanol in wsrer (since some of the compuunds being a n a k ~ e dconrain ionizable acidic Drotms, the addirion of -J"i acetic acid to the methanol:wate~mixtur&assures acceptable oeak svmmetries-this is a standard chromatoara~hictechnique known as ion-suppression ( 4 ) . Figure 2 ifiuitrates the
I OH
baseline separation obtained for all components using a 30 cm X 3.9 mm i.d. C-18 column and 35% aqueous methanol (4% acetic acid added) as the mobile ahase. After adjustinithe mobile phase to obtain resolution of all com~ounds.the students were reouired to identifv, each oeak in tl;e chro&tngram. This is eas'ily accomplished either by iniection o i a solution rontainine each standard individuallv o'by add in^ the irand:jrd: one HI a time to the soluti
