in this issue HPLC: A Practical Technique for Future Chemists Chromatography is a relatively recent addtion to the chemist's list of analytical techniques. M. Tswett's seminal paper was published less than 90 years ago, in 1906. Based on the f a d that the components of a mixture travel a t different rates through a medium because of their varying adsoption by that medium, chromatogrphy allows separations of a wide variety of mixtures in either the gas or liquid state. Thus, a whole family of chromatographys has grown up, with myriad applications in many areas of chemistry. High-performance liquid chromatography (HPLC) is one of the popular members of this family, and the three experiments in our Modem Student Laboratory section this mouth illustrate its versatility. The most common use of all the chromatographic techniqnes is for separating mixtures into their components for individual identification. HPLC has been particularly helpful in separating the large molecules dealt with in biochemistry, and, therefore, i t is essential that future chemists know how to use this technioue routinelv. Commercial HPLC units usually include a UV-detection device t11 cornolete the identification stco of the analvsis. This twical instrumentation is used b i Clapp, ST&, and ~ y e c h -
260
Journal of Chemical Education
mann (page A122) in their experiment that identifies amino acids in unknown dipeptides. When a photodiode array detector is added to the chromatographic apparatus, even more versatility is achieved, since a complete spectrum can be taken a t any point in the run,which aids in the quatitative analysis of selected trace compounds and allows monitoring of peak purity. Remcho, McNair, and Rasmussen (page A1171 point out these important features and present an experiment that demonstrates the utility of this appmach and also serves as an introduction to retention theory in reversed-phase HPLC. Although HPLC is thought of as an analytical technique, it can also be employed for kinetic determinations. Braco, Bafi6, and Abad (page A1131 use it to monitor the progress of a reaction by separating the species under study. The experiment illustrates "a nonmnventional, but very instructive, application of liquid chromatography.'' While it is important for students to learn HPLC technioue for its own sake. all of these ex~erimentahave an adhcd pedagogx value.'~achone cxplois compounds that have oractical, real-life imolicationti: an antihiotic,. . oreservativis and pfasticizers, and amino acids.
