Week 6 TLC of Analgesics Today’s Agenda: Analgesics Polarity Thin layer chromatography. Constructing a report.

In your groups, summarize what you know about pain killers. How do they work? What’s the best? Pain Killer Comparison

Extracting pain killers Let′s think! Extracting pain killers In your groups review your responses to the following pre-lab question and come up with a consensus answer. Using the Summary of Steps given in section 7-1 of the lab book and the notes from the experiment guide as your guides prepare a set of directions for extracting the analgesics from one pain-killer tablet.  Make sure to include all the materials and equipment you expect to use. 

Thin Layer Chromatography (TLC) In your groups discuss what TLC is. explain how TLC will be used to identify the components of OTC pain killers. give the chemical explanation for how TLC can achieve separation of chemical compounds.

What makes a molecule polar? Let′s think! POLARITY What is it? What makes a molecule polar?

POLARITY Why does it matter? Let′s think! POLARITY Why does it matter? The solubility of one substance in another depends on the relative strength of the attractive forces between their particles AA , BB >> AB Insoluble, Immiscible AA, BB <= AB Soluble, Miscible Or, more commonly, “like dissolves like”

Animation: http://www.youtube.com/watch?v=SdYb6GgBQ7s Chromatography Separation based on unequal attractions between the different components of a moving mixture an a stationary phase. Animation: http://www.youtube.com/watch?v=SdYb6GgBQ7s Mobile phase Stationary Support

BASED ON MOLECULAR INTERACTIONS PREDICT HOW WILL MOVE THROUGH THE TUBE Imagine we inject a substance composed of molecules that have weak attractive forces with the STATIONARY PHASE MOBILE PHASE or ELUTANT BASED ON MOLECULAR INTERACTIONS PREDICT HOW WILL MOVE THROUGH THE TUBE

BASED ON MOLECULAR INTERACTIONS PREDICT HOW WILL MOVE THROUGH THE TUBE What if we injected molecules with strong attractive forces with the stationary phase? BASED ON MOLECULAR INTERACTIONS PREDICT HOW WILL MOVE THROUGH THE TUBE

Suppose we put a mixture of two solutes and one solvent (mobile phase) into our coated tube. What do you expect to happen? What will happen if more solvent is added?

With the proper selection of stationary and mobile phases you can separate materials based on intermolecular forces. Gas chromatography

Analgesics Pre-lab

Polarity of analgesics Let′s think! Polarity of analgesics In your groups review your responses to the following pre-lab question and come up with a consensus answer. Which of the known compounds you'll be evaluating - aspirin, acetaminophen, ibuprofen and caffeine - is the most polar.  Explain why you believe  your choice to be the most polar.

Extraction Pointers Best performed in a centrifuge tube Let′s review! Best performed in a centrifuge tube Do not overheat the extraction mixture. The whole pill will not dissolve. For the pill with a coating make sure you crush it up real good. Centrifugation may be needed to remove solids. Use no more than 5 mL of solvent Extraction Pointers

Polarity of analgesics Let′s think! Polarity of analgesics In your groups review your responses to the following pre-lab question and come up with a consensus answer. Describe how you will go about performing TLC on the various samples listed in the experiment guide (assume that the various pills have already been extracted).  Use the outline given in chapter 8 of the lab book.  Make sure to detail all the equipment and materials you expect to use.

Rf What does Rf stand for? Why are Rf values needed? What will you need to be able to calculate Rf values?

TLC pointers Let′s review! Each plate can accommodate four spots. You will have many more to run. Have a plan. How to evaluate consistency amongst plates? don’t cover the spots with solvent! Mark the solvent front and circle the spots. Use pencil & don’t forget – capillary tubes are GLASS WASTE!

UV Light – can damage the retina. Avoid looking at the lamp. Seeing Spots Safely REMINDER UV Light – can damage the retina. Avoid looking at the lamp.

Caution – iodine stains the skin. Fumes are acrid Seeing Spots with Iodine Caution – iodine stains the skin. Fumes are acrid To work effectively, the iodine needs to come in contact with the plate. After securing the plate in the chamber, shake it to coat the plate with the iodine powder.

Thin Layer Chromatography Let′s explore! Today’s Challenge Thin Layer Chromatography Available resources: TLC plates. Solvent: use .1% acetic acid in ethyl acetate Your aspirin, reagent grade aspirin and an aspirin tablet. You have 45 minutes

The Report To be submitted next week: Introduction. Background information necessary to understand the experiment. Results. An organized presentation of the results obtained. Discussion. A discussion of the results obtained, their credibility and their meaning. You are to write a complete report for all three weeks of this experiment. To be submitted BEFORE leaving class or included in the report as appendices: Raw data. A copy of all measurements and observations you collected in lab. Calculations. Examples of the percent yield and Rf calculation.

Discussion Your report will need to address the following Discuss your yield of aspirin. Is it a good yield? Defend your opinion. How pure is your aspirin? Discuss whether or not your aspirin is pure enough to be consumed. Can your yield be improved upon? How and where? Discuss what you discovered in each of the six OTC pain killers. Did you observe any evidence of additional components (other than the four knowns)? Discuss what variation, if any, was observed from plate to plate and how this affects the credibility of your conclusions.