HPLC Lab
SCHA-319
Separation of the Components of Excedrin
And diet cola Using Reverse Phase HPLC
High Performance Liquid Chromatography (HPLC) is a very powerful and commonly
used separation method. Its applications range throughout the chemical, biochemical
biological and pharmaceutical sciences. HPLC has two major advantages over gas
chromatography. First, for GC the analytes must be volatile (only 15% of all compounds
fit this requirement) and second, the mobile phase only serves as a mass transport
function, since gasses make very poor solvents. In HPLC we only need compounds that
are soluble in our mobile phase and we can use mobile phases with differing solvating
powers and thus gain a greater level of control over the separation process.
In this lab we will separate and quantify the amount of caffeine, acetaminophen and
asprin present in Excedrin formulations and will compare this to the amount in a generic
product. We will also examine a diet cola product and quantify the amount of caffeine
present.
The stationary phase used in this lab is the standard packing used most commonly which
is octadecylsilane (or C18). The mobile phase we will use is a mixture of methanol and
water to which a small amount of acetic acid has been added. The mobile phase is very
polar and compounds that are more polar will spend more time in the mobile phase and
thus elute more quickly than less polar compounds.
Procedure:
Prepare your tablets and standards in A335.
Note: Filter sufficient amount of the solutions to proceed to the next dilution step. All
samples injected into the HPLC must be filtered.
You should weigh your tablets before you grind them up so you can determine the
percent active ingredients in a tablet. Cite this value in your report.
Solution 1. Grind up a single Excedrin and dissolve the powder in 65 mL of methanol.
Transfer this solution to a 100 mL volumetric flask. Fill to the mark with 1% Acetic acid
in water. Filter enough of this solution to get 2.00 ml of this solution and dilute up to
25.0 ml in a volumetric. This is your scouting solution. Transfer this solution to an
HPLC vial. Cap and label this vial.
Solution 2 and 3. Also prepare a generic tablet and a Canadian tablet in the same way as
for solution 1.
Solution 4. Acetaminophen Standard. Dissolve 25 mg of Acetaminophen in ~65 mL of
methanol. Transfer this solution to a 100 mL volumetric flask and fill to the mark with
the 1% acetic acid in water.
Solution 5. Asprin Standard. Dissolve 25 mg of Asprin in ~15 mL of methanol.
Transfer this solution to a 25 mL volumetric flask and fill to the mark with the 1% acetic
acid in water.
Solution 6. Caffeine Standard. Dissolve 20 mg of caffeine in ~15 ml of methanol.
Transfer this solution to a 25 mL volumetric flask and fill to the mark with the 1% acetic
acid in water.
Transfer, with filtration, solutions 4- 6 to labeled HPLC vials.
Bring these solutions to A173 for analysis.
Use the sequence table to automate your analysis to capture the quantitative data. You
may start with SCHA319 and modify it. Use Method - SCHA319. Discuss with your
lab instructor the various parameters in the method.
Using solution 1 modify the percentages of the mobile phase components. Comment in
your report on the effects you see. Modify the wavelength of detection. What effect
does this have?
Each run takes about 6 minutes. So you have plenty of time to modify things. Select
other parameters to modify. What effect do these modifications have?
Set up and start your sequence. Run the various tablet samples and your single
compound standards. While the first data is being collected for the first several samples
you may return to A335 and prepare your standards for the quantification part of the
experiment. You sequence may be modified, i.e. added to, on the fly. The method
cannot be.
As part of you sequence Run a sample of the Excedrin that has been sitting in solution for
a while. Do you see four peaks from a sample that has been sitting around for a while?
Why would that be? What is the extra compound?
Additional samples.
Solution M1. Prepare a solution that has a filtered 0.500 ml of each of the actives
(solutions 4 – 6) diluted up to 10.0 mL of mobile phase in a volumetric.
Solution M2. Prepare a solution that has a filtered 1.00 ml of each of the actives
(solutions 4 – 6) diluted up to 10.0 mL of mobile phase in a volumetric.
Solution M3. Prepare a solution that has a filtered 2.00 ml of each of the active
(solutions 4 – 6) diluted to to 10.0 mL of mobile phase in a volumetric.
Solution M4. Prepare a solution that has a filtered 3.00 ml of each of the active
(solutions 4 – 6) diluted to to 10.0 mL of mobile phase in a volumetric.
From the data in solutions M1-M4 and the values obtained from solutions from the three
tablets report the amount of the three actives in the three different products. You will
need to prepare a calibration curve to do this (use Excel). Pay attention to the dilutions
you made and be aware that the FDA will not allow massive deviations from the bottle
assay. Comment in your report on what your sources of error might be. I suggest that
you plot milligrams of the actives on column and then factor back all you dilutions to get
assay results in mg per tablet. Good practice calls for you to do at least duplicate
injections for the quantitative standards and the unknowns.
You should also make a blank injection.
Include a sample of flat diet Pepsi. What is amount of caffeine in a 12 ounce can. How
does this compare to the expected amount. (Search the web) What might be the other
peaks in this assay. Run a suspect or two.
What are the structures of the actives? These should be included in your report.
You may depart the lab when you quantitative data collection has started. This is one of
the major reasons we have an auto sampler. Your sequence should has a shutdown
procedure included. Your instructor will assist you with this.
For your report you should show the structures of the three main components of the
Excedrin tablet. You should also calculate the number of plates on the column and H for
the column. Use the first major peak to calculate this. You should also calculate the
resolution between the first two peaks in the Excedrin tablet.