Thin Layer Chromatographic Separation of Common Analgesics-A
Consumer Experiment
organic compounds. ~ & the m tlc experiment studentilearn not only the basic principles of chromatography hut also those of polarity and solubility. No student should go through a course in organic chemistry without completing a t least one exoeriment in tlc.
h) alwut 10.1itudtnts in R lirst s w n e i l ~ urgnnir~htmisrr) r latwmtory. C h a m h r thiq rrprrimmt nre six co!nmamlg usrd, over-thr-muntrr anolgeiivs; hnarin ?, H d y w .4~1)irin@. llufftrin~, Kmprrm ' , Kxrrdrm' a d 'l'ylend?. The nrtiw ingredients nhirh arc cunlilincd -1ngly o r in comhinatim in the.+ grrpnrations are acetammophen, aspirin, caffeme, phenketin, and salievlamide. A descriition of the experimental procedure is given below. Grind one tablet each of the six analgesics into a powder and extract with 5 ml of chloroform. Draw out several micro capillaries from open-ended capillary tubes. Obtain two 5 X 10emEastman #I3181 100 p silicagel tlc plates impregnated with fluorescent indicator. On a horizontal line about 1cm from the bottom, apply the six analgesic extracts using a clean miero-capillary for eaeh. Prepare a developing chamber from an 800-ml beaker covered with a watch glass and containing a strip of filter paper. Placein the chamber about 20 ml of developingsolvent composed of a 2:9:9 mixtureof n-butyl alcohol, methyl isobutyl ketone, and ethyl acetate, respectively. Place the tlc plate in the developing chamber, and allow the solvent to rise to within 1 cm of the top. Remove the plate and allow the solvents t o evaporate. Then use ashort-wave uv source to visualize the separated components, and outline eaeh spot with a pencil. Measure the distance traveled ofeaeh component compared to the solvent front and compute Rf values. In ,order to identify each separate component of the above preparations, i t is necessary t o determine the Rf values of standard samples. On the second tle plate, apply solutions (1 g/lW ml chloroform) of the known ingredients as above. Develop the plate and measure Rf values as before. Under the present conditions, the Rf values for the component ingredients are: acetaminophen (OX), aspirin (0.15, caffeine (0.35), phenacetin (0.661, and salicylamide (0.67). I t will be noted that phenacetin and salicylamide have identical Rf values. In fact, these two compounds were completely inseparable under all conditions attempted. They are, however, easily distinguishable, since salicylamide exhihits a brilliant blue fluorescence when exposed to short wave uv lieht. Moreover, none of the analgesics used contains both salicylamide and phenacetin. Thus, in a relatively simple experiment requiring 2-2'12 hr, including a short discussion period, students are able to separate and identifv the active inmedients of several common analeesics. In so doine. -. the".also eain hands-on experience with a very important and useful Gboratory technique. Metropolitan State College Russell A. Cormier Denver, Colorado 80204 William B. Hudson J a y A. Siegel
180 / Journal of Chemical Education
