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

(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)

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

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 (400-700 nm). Prism Violet:   400 - 420 nm  Indigo:   420 - 440 nm  Blue:   440 - 490 nm  Green:   490 - 570 nm  Yellow:   570 - 585 nm  Orange:   585 - 620 nm  Red:   620 - 780 nm White light White light

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

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 =

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;

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

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

Experimental contents 2. Generate absorption curve of ASA Unico7200 Adjust the wavelength control knob (250-290nm) 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

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 ? 　?

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

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

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?

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