CH 461/461H

Sample Preparation for Experiment 2A - Vitamin Pills

    You will analyze a commercial Vitamin B Complex tablet for the amount of vitamin B2. This B Complex formulation contains B2 and other B vitamins and other inert materials (e.g., starch & inorganic binders) that you will not be determining at this time. Measure the weight of one intact vitamin tablet to 0.1 mg. Crush the tablet using a mortar and pestle and make three test solutions using about 1/10 of the tablet weight (-0.1 g) for each solution. Weigh the solid into separate clean labeled medium sized test tubes (obtain from instructor). You will need to know the actual mass used for each of the three sample solutions to a precision of 0.1 mg. Record all weighing data in your lab notebook and attach carbon copies to your final report.
    For each of the three sub-samples in test tubes, add 10 mL of the solvent mixture of 80/20 MeOH/H₂O and add 2 mL of glacial acetic acid with the aid of a 10-mL graduated cylinders. CAUTION: methanol is toxic: wear gloves, keep off skin, etc.; glacial acetic acid is a concentrated acid (99.8 wt%). Warm the test tubes with occasional shaking or swirling at 60 °C in one of the driblock heaters for 45-60 min (record the time used). CAUTION: Be especially careful not to point the test tube toward yourself or others when heating. Note that some solid inert materials and binders will not dissolve. Cover each test tube with aluminum foil. Store all 3 solutions (even if you do not get to the dilution or transfer) in the refrigerator in the balance room on the 3rd floor. All bottles should be clearly labeled with identification including class, date, and group number.
    Cool the contents to room temperature in a cold water bath and quantitatively transfer the entire contents of each test tube into a separate labeled clean 100-mL volumetric flask. To quantitatively transfer means to carefully rinse the test tube with solvent using the wash bottle into the volumetric flask without losing any analyte solution (OK to leave solids behind). Finally, dilute to volume with MP water. These solutions will be designated as X solutions, e.g., X1, X2, & X3. After mixing thoroughly, allow the flasks to stand undisturbed for 1 min to allow the undissolved materials to settle. Transfer solution X for each sample into clean labeled 125-mL amber bottles for storage. Note: be sure to rinse the bottle with a little of the solution to be stored in it before transferring the remains of solution.
    Make a quantitative 1/5 dilution of solution X for each sample in a 50-mL volumetric flask using MP water as the solvent. Transfer these solutions, denoted as Y solutions (Y1, Y2, Y3) to clean and rinsed 125-mL amber bottles as you will need the flasks. Label the bottles and store these bottles in the refrigerator when not in use.
    Because solution X contains considerable methanol, when it becomes time to dispose of it, dispense into a waste container in the hood marked "non-halogenated solvents" and log in the amount recycled on the nearby clipboard.