PhilaU CHEM 201L - Analysis of Analgesic Tablets by Thin Layer Chromatography (19 pages)

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Analysis of Analgesic Tablets by Thin Layer Chromatography



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Analysis of Analgesic Tablets by Thin Layer Chromatography

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Pages:
19
School:
Philadelphia University
Course:
Chem 201l - Organic Chemistry I Laboratory
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Analysis of Analgesic Tablets by Thin Layer Chromatography TLC Organic Chemistry Lab I Fall 2008 Dr Milkevitch Oct 12 14 2009 Separating Molecules Today Learn a separation technique Molecules can be separated by a number of methods Extraction Precipitation Chromatography Chromatography to write in color Originally developed to separate components of inks Thin Layer Chromatography Thin Layer Chromatography The separation of moderately volatile or nonvolatile substances based upon differential adsorption on an inert solid stationary phase immersed in a organic solvent or solvent mixture mobile phase Makes use of A stationary phase solid support Mobile phase a fluid Basic principle of separation Differential interactions of molecules with these 2 phases How the separation works Molecules can move with the mobile phase Or they can remain fixed on the stationary phase Called partitioning How molecules partition between the 2 phases depends on Properties of the phases Properties of the molecules being separated How this works continued Molecules that partition into the mobile phase Will move more rapidly than molecules that partition into the stationary phase Therefore they will separate from those that are partitioned into the stationary phase Faster moving component partitioned more into mobile phase Slower moving component partitioned more into stationary phase Solvent movement Two component mixture applied to TLC plate Nuts and Bolts of the Method You must carefully select mobile and stationary phases to achieve full separation of mixtures of molecule Trial and error Stationary phase thin layer of silica spread on a surface Mobile phase solvent system that migrates through the silica Samples are spotted on the plate Moved along by the solvent s migrating through the silica Rf Values Molecules that are separated will migrate as spots and their migration can be measured Migration usually reported as an Rf value Calculation of an Rf value Ratio of sample migration how far spot moved to solvent migration how far the solvent moved Can be used to identify components in a mixture Compared to standards Today look at the components of analgesic tablets by TLC Look for the actives Calculating an Rf Value Solvent Front Solvent Front 5 cm Origin Spot 1 Spot 2 Spot 1 moved 1 cm Rf 1 5 0 2 cm Spot 2 moved 4 cm Rf 4 5 0 8 cm Analgesic Medications Analgesia Greek for the deadening or absence of pain without loss of consciousness Analgesics compounds that relieve pain Range from aspirin to morphine and other related narcotics Many OTC over the counter analgesics available Tylenol Advil Excedrin Aspirin various preparations Actives OH O N OTC analgesics contain many compounds The active is what relieves pain Other compounds are binders flavorings colorants stabilizers solubility enhancers Paracetamol acetaminophen O OH Ibuprofen N N O N N O Caffeine Procedure Obtain a silica gel plate from me This plate will have a UV indicator in it Draw a straight line lightly in pencil approximately 2 cm from the bottom edge of your TLC plate Use a ruler to do this This is called the origin Draw a straight line lightly in pencil about 1 cm from the top edge of your TLC plate Again use a ruler to do this This is called the solvent front Mark 5 spots in pencil along the origin Distribute the spots evenly along the origin Obtain the TLC standards These are solutions of known components of the analgesic tablets They include Caffeine Acetylsalicylic Acid aspirin Ibuprofen Acetaminophen Procedure con t Spot the TLC plates with the TLC standards and 1 unknown Use a spotting capillary or the small diameter plastic dropper Make the spots small approx 1 mm in diameter Before you do this ask me or Scott Nicole to demonstrate on your plate Preheat the TLC plate in the 50 C oven for 5 min This will dry the spots Sometimes you will need to dry the plates for a longer period of time What your TLC Plate will Look Like Solvent front drawn lightly in pencil origin Procedure con t Make a TLC tank called a developing tank Use a 250 ml beaker Add a few ml of the mobile phase to the beaker Mobile phase ethyl acetate Place a piece of filter paper in the beaker Will allow the beaker to fill with solvent vapor Cover TLC tank with a watch glass parafilm TLC Tank Watch glass Filter paper Mobile phase Developing Place TLC plate spotted in the tank Solvent level must be below the origin otherwise you ll lose your spots Tilt plate over a bit onto the side of the beaker Shouldn t touch the filter paper Watch the migration of the solvent Remove the plate from the TLC tank when the solvent is exactly at the solvent front line Let the plate dry Visualize the plate using the UV box See me to demonstrate use of the UV box After this further develop the plate in the iodine tank Iodine will react with the spots Makes the spots yellow When fully developed remove and circle the spots with pencil Results Measure the distance the solvent mobile phase traveled Bottom to the solvent front line Measure the distance from the center of each spot to the origin Calculate Rf values for each spot Rf Distance spot traveled Distance solvent traveled Results II Attempt to identify what the spots are in your unknown Compare the Rf values of the standards versus the Rf values of the spots in your unknown If they match closely then you have that component in your unknown Can you identify what unknown you have Possibilities Advil Tylenol Excedrin Be sure to draw a figure of your TLC plate Identify all standards and all spots Show calculations of your Rf values Conclusions Things to Think About What can we conclude Did your TLC plate work Were you able to spot your plate successfully and develop the plate Did you see the spots for the standards For your unknown did you see a spot or spots Were you able to resolve the different spots Did the spots separate from each other This is what we are trying to do Could you identify your unknown See me for the identity of your unknown If you did then you have successfully utilized TLC to identify your unknown compound


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