STABILITY/KINETICS OF ASPIRIN HYDROLYSIS
to write about this experiment uploaded:
-Purpose:
-Hypothesis:
-Introduction:(how is it relevant to industry of pharmacy
PHSC 419/515
STABILITY/KINETICS OF ASPIRIN HYDROLYSIS
Laboratory Procedure:
Note: All samples are analyzed for SA molar concentration at 310 nm (all readings must be below 1.000 absorbance unit)
? Each group will be assigned one pH buffer
? You will need to prepare a new calibration curve for SA with standards you prepare from the stock (0.5 mM) SA. (3 dilutions/data points plus 0,0)
Hydrolysis process:
• At the assigned pH buffer (pH 7)
• At two temperatures (45° and 65°C), and
• Collect and analyze samples after each hydrolysis period of 45, and 90 minutes
Provided: Heated pH buffer solutions (assigned in class): placed into two temperature baths (45°C and 65°C).
1. Accurately weigh 150 mg ASA powder and quantitatively transfer it to a 125 mL conical flask. Add 2 mL of Ethanol and completely dissolve the ASA. Add 48 mL of the assigned hot buffer solution from one of the two temperature water baths; begin timing of the hydrolysis process.
2. Thoroughly mix the solution and place the flask in the same temperature water bath (from which the buffer solution was taken)
3. Remove 0.25 mL sample from the flask after each hydrolysis time interval of approximately 45 min, and 90 min (record your exact time), dilute it to 10 mL with water, and analyze the diluted sample for SA concentration [M] at 310 nm; further dilution may be necessary to get absorbance values below 1.000.
4. Follow the hydrolysis reaction by analyzing all samples.
5. Record absorbance values and dilution factors (where required) for all samples.
6. Follow steps from 4 to 6 for the samples from the second temperature water bath.
Topics to be included in typed documents:
1. Results/Discussion
a. Determine the concentration [mM] of SA present in each hydrolysis sample at time X, (use the SA Calibration Curve)
b. Calculate the concentration [mM] of ASA remaining at each sample time by subtracting the SA conc [mM] (remember for each mole of ASA hydrolyzed, one mole of SA is formed) from the initial ASA concentration
c. Plot natural log (ln) ASA [mM] remaining vs. time (min) for each temperature
d. Determine the slope (= K app) of the line at each temperature
e. Determine Ea from the equation Log (K2/K1) = Ea(T2 – T1)/2.303xRxT2xT1
f. Plot natural log (ln) Kapp vs. 1/T (K) – temperature in Kelvin – and determine the slope = E a /R; determine the activation energy (E a ) for the hydrolysis of ASA; where R=1.987 cal/Kmole
g. Compare the Ea from the two methods
h. Determine the Kapp at body temperature (37°C) using the same equation as in e
i. What’s the half-life (T½) for ASA solution at 37°C and pH 7?
j. What is the relevance of this value?
