In the Laboratory
Identification and Quantitative Analysis of Acetaminophen, Acetylsalicylic Acid, and Caffeine in Commercial Analgesic Tablets by LC-MS Christopher J. Fenk,* Nicole M. Hickman, and Melissa A. Fincke Department of Chemistry, Kent State University Tuscarawas Campus, New Philadelphia, Ohio 44663 *
[email protected] Douglas H. Motry Department of Chemistry, Kent State University Salem Campus, Salem, Ohio 44460 Barry Lavine Department of Chemistry, Oklahoma State University, Stillwater, Oklahoma 74078-3071
Integration of modern instrumentation into the undergraduate setting is becoming increasingly important as more advanced technical knowledge and skills are expected of college graduates. With the plethora of instrumental methods now available in modern chemistry laboratories, great emphasis must be placed on the judicious selection of appropriate methods for introduction into the undergraduate setting (1). Considerations that weigh heavily in this selection are instrumentation cost, ease of use, availability, general maintenance, and range of application. A powerful and emerging analytical technique that is conspicuously absent from the undergraduate curriculum is liquid chromatography-mass spectrometry (LC-MS). Over 80 undergraduate laboratory experiments that exemplify gas chromatographymass spectrometry (GC-MS) techniques have appeared in this Journal (including recently refs 2-5)). Conversely, only 8 references to undergraduate LC-MS experiments have been reported in this Journal (6-14). Of these, only one takes advantage of both the separating power of liquid chromatography and the quantitative ability of mass spectroscopy (6). However, this article uses tandem mass analysis to quantify the amount of analyte in the matrix being investigated and does not require the use of the dual-detection mode available on many LC-MS instruments. LC-MS, unlike its counterpart GC-MS, has yet to be incorporated into the undergraduate curriculum in a meaningful way. The reasons for this discrepancy are numerous. Liquid chromatography is often considered problematic for use in the undergraduate setting. This is due primarily to long equilibration times necessary between chromatographic runs when optimizing separation conditions and the relatively high maintenance of LC systems as compared to GC systems. LC-MS was also slower in its development than GC-MS owing to the significant problem of sample molecule detection in the presence of large volumes of solvent. These problems are now rapidly being overcome with the advent of microsampling techniques and improved detection methods for analyte molecules (i.e., thermospray and electrospray ionization). The introduction of microcolumn technology to LC has facilitated the use of MS detectors and the incorporation of LC-MS into the undergraduate curriculum. Column flow rates of 0.25 mL/min or less with total column volumes of less than 838
Journal of Chemical Education
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0.5 mL are common. This allows for rapid column equilibration (
