Aspirin is toxic in high concentrations.
That's why aspirin tablet manufacturers must ensure that their product contains
between 90% and 110 % of the amount of active ingredients stated on the label.
Does your brand of aspirin pass the test?
In this video, you will learn how to use PASCO's UV-Vis Spectrometer
to analyze the aspirin content in an aspirin tablet as an application of Beer's law.
[Analysis of Aspirin Tablets]
The solution preparation and analysis techniques in this video can be applied
to any one-solute solution that absorbs light between 180 nm and 1,050 nm.
You'll need a Windows or Mac computer and the latest version of the Spectrometry app,
which is available for free at pasco.com/downloads.
The chemical name for aspirin is acetylsalicylic acid, or ASA for short.
You can determine the amount of ASA in an individual 325 mg aspirin tablet
by comparing the absorbance of several colorless ASA solutions of known concentrations
against the absorbance of a solution made from an individual aspirin tablet.
ASA degrades fairly quickly in solution,
so all solutions should be used within an hour or so of mixing.
First, mix 100 ml of a 2.2 mM stock ASA solution.
Make this by dissolving less than a gram of solid ASA in 95% ethanol in a volumetric flask.
So you'll need an analytical balance readable to the ten-thousandths place.
Next, five solutions labeled A through E are made by taking 2, 4, 6, 8, and 10 ml of stock solution,
and diluting each to 100 ml with distilled water in a volumetric flask.
Students must use the dilution equation M1V1=M2V2 to calculate the new concentration of each solution
based on the volume of stock solution used.
Next, a calibration solution is made by mixing 0.8 mL of 95% ethanol
with 9.2 mL of distilled water.
Now you can construct the calibration curve for an ASA absorbance versus concentration graph.
Use quartz cuvettes for best results.
Fill each cuvette three-fourths full.
Handle each cuvette by the frosted sides,
and wipe the clear sides with a lint-free lens wipe before placing in the spectrometer.
Orient the cuvette so that light travels through the clear sides from the light source to the detector.
Start with the calibration solution.
First calibrate dark, then calibrate light.
Next, I need to use an ASA solution to choose an appropriate analysis wavelength.
I'm choosing solution D,
since it is neither the most concentrated nor the most dilute in the series.
Start recording data and make the adjustments necessary to improve the data display.
I'm going to change the number of averaged scans.
And increase smoothing.
Then I'm going to move the coordinate tool to a distinct peak,
and select the check mark to set the analysis wavelength.
Now I'll stop recording data and go to the Concentration tab.
The concentrations for each solution are reported in millimolar,
so you'll need to change the unit in the table.
Millimolar is the same as millimoles per liter.
Update the concentration values in the table
to match your calculated values for solutions A through E.
Start recording data.
Starting with solution A,
click the check mark to keep that solution's absorbance value.
Next go to B,
C,
D,
and lastly E.
Notice all my absorbance values are very close to or below 1, as they should be.
I can add a linear fit to get the slope,
and I can scale the data.
We'll need the slope, m, and y-intercept, b, for a later calculation.
Now it's time to determine the absorbance of an aspirin tablet solution.
To make the solution, first record the exact mass of an aspirin tablet.
Then grind it to a very fine powder with a mortar and pestle.
Measure about 0.04 g of the tablet powder.
Record the exact mass collected.
Bring the solution to volume with ethanol in a 100 mL volumetric flask.
Then use a quantitative filter apparatus to remove impurities from the solution.
This system uses a simple hand-operated vacuum pump,
but your setup may incorporate a water aspirator.
Take 6 mL of the filtrate and add it to a 100 mL volumetric flask,
but this time bring the solution to volume with distilled water.
Then add the solution to a quartz cuvette.
Record the absorbance of a solution of unknown concentration
here in the bottom table in the Spectrometry app.
Once you have the absorbance, which is the y value from the graph,
you can either estimate the concentration based on where the absorbance value intersects the slope,
0.514 is about here,
or, even better, use the linear equation y=mx+b to find the x-axis value, which is concentration.
Just plug in y, m, and b to solve for x.
You can enter your calculator- estimated concentration in this box,
and the app will plot the point for you.
The closer your data point is to bright green,
the closer your value is to the concentration predicted by the linear fit.
Once you are confident in the concentration, you can calculate the mass of ASA in the original tablet.
Then you can compare that mass to the 325 mg value stated on the bottle
to see whether the aspirin mass falls within plus or minus 10% of 325 mg per tablet.
For more investigation ideas with the UV-Vis Spectrometer or other equipment,
visit pasco.com.
Thanks for watching and see you next time.