1. Concentration determination of acetylsalicylic acid by using ultraviolet spectrometer
Liang Zhang
03/25/2016

2. (acetylsalicylic acid, ASA)
Extracts H2SO4
Willow bark Salicylic acid (SA) Acetic anhydride Acetylsalicylic acid Acetic acid
(ASA, Aspirin)
Medical use:
Treat pain (Headache), fever, and inflammation
Prevent heart attacks, strokes, and blood clot formation
Prevent certain types of cancer (colorectal cancer)
Adverse effects:
Allergic reactions (hives, swelling, and headache)
Temporary tinnitus (ringing in the ears)
Increase the risk of gastrointestinal bleeding
Reye's syndrome (acute encephalopathy and fatty liver, children under 16)

3. Experimental Section:
Theoretical Section:
What
is Characteristic Spectrum (Beer–Lambert law)
What
is the principle of spectrometer
Experimental Section:
How
to use a UV spectrometer
How
to generate a standard calibration curve
How
to determine the concentration of ASA in solution

4. Spectrum
The spectrum is the range of all types of electromagnetic (EM) radiation.
Visible light
Energy that travels and spreads out as it goes in universe;
Mixture of γ-Ray, X-Ray, UV, visible light, Long radio waves;
A mixture of single wavelength lights;
A prism or the atmosphere can separate the lights;
Visible Light is a small portion of spectrum ( nm).
Prism
Violet:   nm 
Indigo:   nm 
Blue:   nm 
Green:   nm 
Yellow:   nm 
Orange:   nm 
Red:   nm
White light
White light

5. Characteristic Spectrum
When visible light goes through a cuvette filled with solution sample containing pure individual element, a certain wavelength light will be absorbed rather than a continuous range of wavelengths, and the human eye sees the complementary color to that which is absorbed.
Visible light
Prism
The maximum absorption of acetylsalicylic acid in solution
max: 250~290nm

6. Ultraviolet spectrometer and Beer–Lambert law
Unico7200
Beer–Lambert law:
The absorbance (A) of a material sample is directly proportional to both the concentration of the attenuating species (c) as well as the thickness of the material sample (ɭ)
A = =
c : Concentration of the sample
ɭ : Length of light transmitted
ɛ : Extinction coefficient 
UV spectrometer Cuvette holder ɭ
I : Intensity transmitted
I0 : Intensity before transmittance
A : Absorption
A =

7. Experimental contents
1. Preparation of four ASA solutions (dilution);
2. Generate absorption curve of ASA to determine max ;
3. Determine the absorption value of each samples under max ;
4. Generate the standard calibration curve;
5. Determine the concentration of ASA in unknown solution;

8. Experimental contents
1. Preparation of four ASA solutions
Standard solution: 1 mg/ml
Blank
Solution-1
Solution-2
Solution-3
Solution-4
Volume from standard solution (ml) 3 4 5 6
Distilled water
Add to 50ml
Bottom of
meniscus
Curve
mark
Fill pipette by suction Remove bulb Adjust the level Drain Never blow out
above the curve cover stem with finger to the curve remaining amount
Adding water Calibration (dropper) Reverse to mix

9. Experimental contents
2. Generate absorption curve of ASA (Blank and Solution-4)
Only hold on the frosted side Transfer the solution Reach 2/3 height Wipe clear sides
(Blank or solution-4) cap the cuvette carefully
Do not hold it too long
Unico7200
Sample lid
Handle
Monitor
Wavelength control knob 1 2 3 4
1 2
UV light
Handle
Handle
Open sample lid Insert the cuvette (Blank to position-1, solution-4 to position-2)
Pre-warm 30mins Make sure: Clear sides are on the light pathway (double check).
Position-1 is on the light pathway (pull or push the handle to adjust).
Then close the lid

10. Experimental contents
2. Generate absorption curve of ASA
Unico7200
Adjust the wavelength
control knob ( nm)
Order 1 2 3 4 5
Wavelength (nm)
250
258
264
270
272
Absorption ? 6 7 8 9 10
274
276
278
284
290
Press “Mode” button to select “Transmittance”
Mode
Transmittance
Press “100%” button to calibrate (BLA to 100)
100%
Unico7200
Pull the handle and switch to position 2
Record the value on the monitor
Press “Mode” button again to select “Absorbance”
Mode
Absorbance

11. Experimental contents
2. Generate absorption curve of ASA, and determine max
max
Wavelength (nm)
Absorption
Order 1 2 3 4 5
Wavelength (nm)
250
258
264
270
272
Absorption ? 6 7 8 9 10
274
276
278
284
290
3. Set up the wavelength to max
1 2
UV light
Handle
Unico7200
Adjust the wavelength
control knob (max )
4. Determine the Absorption value (A) of each samples
Blank
Solution-1
Solution-2
Solution-3
Solution-4
Unknown Solution
Absorption ? 　?

12. Concentration of solution
Experimental contents
5. Generate the standard calibration curve
Blank
Solution-1
Solution-2
Solution-3
Solution-4
Unknown Solution
Concentration of solution √ ?
Absorption
Concentration of solutions
Absorption
6. Determine the concentration of ASA in unknown solution

13. Concentration of solution
Experimental reports
max
(1) Absorption curve and max
(2) Absorption value (A) of each samples
Blank
Solution-1
Solution-2
Solution-3
Solution-4
Unknown Solution
Concentration of solution √ ?
Absorption
(3) Standard calibration curve, and equation
(4) Concentration of ASA in unknown solution

14. Quizzes Why do we need to do measurement under max ?
Why do we need blank solution as reference?
Why do the condition of the solutions need to be identical during measurement?

15. THANK YOU