1. RECRYSTALLIZATION, MELTING POINT, and HPLC ANALYSIS of ANALGESICS
Experiment 7:
RECRYSTALLIZATION,
MELTING POINT, and
HPLC ANALYSIS of ANALGESICS

2. Objectives To learn the purification technique of recrystallization.
To further purify aspirin and acetaminophen samples isolated by extraction.
To learn the technique of melting point analysis.
To analyze purity of samples by melting point and HPLC analysis.

3. BEFORE COMING TO LAB… Watch the following videos: Recrystallization
Melting Point Analysis

4. EFFECT OF TEMPERATURE ON SOLUBILITY
At low temperature the substance is much less soluble. (Note that even at low temp. some of the substance will remain dissolved.
At elevated temperature the substance is very soluble.

5. ANALGESICS IN GOODY’S POWDERS

6. PERCENT RECOVERY
Percent recovery: an indication of how much of the active ingredient you were able to recover after the purification method.
HPLC Area %: the percent of the active ingredient present in the sample submitted for analysis.
The percent recovery of compound B is calculated by:

7. OVERVIEW ASPIRIN Reweigh aspirin + filter papers from last lab.
Subtract out filter paper weights to get ACTUAL RECOVERY OF ASPIRIN.
Prepare 2 melting point capillaries of the EXTRACTION ASPIRIN.
Dissolve aspirin in hot ethanol, then hot water, then few drops of hot ethanol.
Cool to room temp, then in ice for 15 minutes.
Suction filter.
Prepare HPLC sample.
Secure small filter paper + aspirin in larger filter paper and submit.
No final weight or melting point sample until next lab!

8. OVERVIEW ACETAMINOPHEN
Transfer acetone/acetaminophen solution from vial to beaker and evaporate acetone completely.
Dissolve acetaminophen in hot water (dropwise).
Cool to room temp, then in ice for 15 minutes.
Suction filter.
Prepare HPLC sample.
Secure small filter paper + aspirin in larger filter paper and submit.
No final weight or melting point sample until next lab!

9. Table 7.1 % Recovery is ≠ HPLC Area % Aspirin Acetaminophen
* Theoretical recovery after extraction (g)
Same # as
Table 6.1
*Actual recovery after extraction (g)
*% Recovery after extraction
Theoretical recovery after recrystallization (g)
Same as…
Actual recovery after recrystallization (g)
Obtain weight during next lab
% Recovery after recrystallization
Actual X 100
Theoretical
Actual X 100
% Recovery is ≠ HPLC Area %

10. OVERVIEW MELTING POINT ANALYSIS
Prepare a melting point capillary containing the provided impure aspirin.
Perform a melting point analysis on this along with the EXTRACTION ASPIRIN prepared above.
Begin MelTemp on setting of 4. Back down temp slightly as thermometer approaches 20o C from the expected melting point (lit value).
Record melting range (Ti-Tf).

11. EXPERIMENTAL PROCEDURE (Melting Point)
Dip the open end of a mp capillary tube into the sample to be tested.
Invert the capillary tube and tap it on the bench top to pack the sample into the closed end.
Insert the capillary tube into one of the slots in the heating block of the Mel-Temp melting point apparatus.

12. EXPERIMENTAL PROCEDURE (Melting Point)
Turn the Mel-Temp power on and adjust the temp control to the desired rate of heating.
In order to obtain an accurate mp, it is necessary to heat
S L O W L Y, at a rate of 2-3oC/min.
Heating too fast may lead to inaccurate results because of insufficient time for heat transfer.
Thermometer
Sample slot
Eyepiece
Power
Temp control

13. Table 7.2 Aspirin Acetaminophen Impure Aspirin preparation (Week 1)
Ti-Tf
---
Extraction sample melting range (oC)
Recrystallized sample melting range (oC)
(Week 2)
Literature melting point value (oC)

14. HPLC retention times (min) and area %
Table 7.3
Sample
Compound
HPLC retention times (min) and area %
Standards
Aspirin
Chromatogram
Acetaminophen Rt
(min)
area %
Samples containing a single compound are considered PURE samples, while those containing both compounds are considered MIXED (IMPURE) samples.
Be sure to attach both sample chromatograms to final lab report!
ANY SAMPLE CONTAINING VISIBLE SOLID WILL BE DISCARDED. Student will receive a penalty for not providing a sample.

15. SAFETY CONCERNS
Ethanol and reagent acetone are both extremely flammable. Keep away from open flames, and use extreme caution when applying heat!

16. WASTE MANAGEMENT
Place all liquid waste from recrystallization in container labeled “LIQUID ORGANIC WASTE”.
Used melting point capillaries should be thrown in the broken glass box, NOT the trashcan!
Any student leaving the melting point capillary tubes in the MelTemp apparatus will receive a technique grade penalty!

17. LABORATORY NOTEBOOK (Pre-lab)
OBJECTIVE (Must clearly state…)
What is the goal of the experiment?
How will you accomplish this goal?
How will you determine if it worked?
TABLE OF PHYSICAL DATA (Complete the following table using MSDS sheets from a site on WWW Links ONLY. Wikipedia is unacceptable)
REFERENCE TO PROCEDURE (Must include…)
full title
Edition
authors
page numbers where actual procedure can be found
Compound
MW (g/mol)
bp (Co)
mp (Co)
d (g/mL)
HAZARDS
Acetone
XXX
Ethanol
aspirin
acetaminophen

18. LABORATORY NOTEBOOK (In-lab)
DATA/CALCULATIONS
ASPIRIN
Weight of large filter paper + small filter paper + aspirin (from extraction)
Actual weight of aspirin (from extraction)
Weight of small filter paper
Weight of large filter paper (for storage)
Experimental melting point of extracted aspirin
Experimental melting point of IMPURE aspirin
HPLC vial slot #
ACETAMINOPHEN
Initial weight of acetaminophen (from extraction)
EXPERIMENTAL PROCEDURE
In paragraph form, describe the procedure that you actually followed during the lab.
Paragraph must be written in PAST TENSE, PASSIVE VOICE.
Include any volumes or weights of chemicals used during the experiment.
Include any mistakes, accidents, or observations if necessary.