Shelf Life Determination

8/10/2019 Shelf Life Determination

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SHELF LIFE DETERMINATION

Santos, G.1, Silverio, A.1, Soriano, R.1, Tan, J.1, Tequillo, H.1

University of Santo Tomas, Faculty of Pharmacy1

Group 8 3F Pharmacy Physical Pharmacy Laboratory

ABSTRACT

The experiment was performed to understand the process of shelf life determination. Acetylsalicylic acid, also

known as aspirin, is one of the most commonly used analgesics worldwide and was used for this experiment. From a

stock solution of salicylic acid, five standard solutions were prepared and their absorbance values were determined

using the UV-VIS spectrophotometer at 296 nm. The best fit line was determined using linear regression. A sample

solution containing aspirin dissolved in water was placed in an oven at 50C. The absorbance readings at 296 nm

were taken after 15, 30, 45, 60 and 90 minutes. From this data, the concentrations of aspirin remaining together with

its logarithmic equivalent were determined. Using linear regression, the best fit line was once again obtained, which

is essential for the computation of shelf-life.

INTRODUCTION

Shelf life is best defined as the time span

over which the quality of a product remains within

specifications. That is, it is the time period over

which the efficacy, safety, and esthetics of a product

can be assured. When the degradation of the essential

components cannot be adequately described by a rate

expression, shelf life cannot be easily estimated or

projected.

Estimation of product shelf-life is done by

two methods estimation from data obtained under

the same conditions as those that the final product is

expected to withstand and the estimation from tests

conducted under accelerated conditions. [4]

Half-life is the amount of time required for a

quantity to fall to half its value as measured at the

beginning of the time period. It is used to describe a

quantity undergoing exponential decay, and is

constant over the lifetime of the decaying quantity.

[8]

Aspirin, also known as acetylsalicylic acid,

is a derivative of salicylic acid. It is the most widely

used medicine in the world. It has the ability to

reduce fever (antipyretic), reduce pain (analgesic),

relieve swelling and pain associated with rheumatism

and arthritis (anti-inflammatory), enhance the

elimination of uric acid (uricosuric), and interfere

with the bodys production of prostaglandins and

their products (thromboxanes), which are associated

with headaches, platelet aggregation and

vasoconstriction. [1]

Aspirin is a part of a group of medications

called nonsteroidal anti-inflammatory drugs

(NSAIDs), but differs from most other NSAIDs in

the mechanism of action. Aspirins ability to suppress

the production of prostaglandins and thromboxanes is

due to its irreversible inactivation of the

cyclooxygenase (COX) enzyme. Aspirin acts as an

acetylating agent where an acetyl group is covalently

attached to a serine residue in the active site of the

COX enzyme. This makes aspirin different from

other NSAIDs (such as diclofenac and ibuprofen),

which are reversible inhibitors. [3]

Aspirin undergoes hydrolysis with the

resultant degradation products being salicylic acid

and acetic acid. [2]

Figure 1. Hydrolysis of Aspirin


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Ultraviolet-visible spectrophotometry (UV-

Vis) is the absorption spectroscopy or reflectance

spectroscopy in the ultraviolet-visible spectral region.

This means it uses light in the visible and adjacent

(near-UV and near-infrared) ranges. The absorption

or reflectance in the visible range directly affects the

perceived color of the chemicals involved. Beer-

Lambert law is most often used to determine

concentrations quantitatively. The instrument used is

UV-Vis spectrophotometer. [6]

The Arrhenius equation is a simple but

remarkably accurate formula for the temperature

dependence of reaction rates. The equation was

proposed by Svante Arrhenius in 1889, based on the

work of Dutch chemist Jacobus Henricus vant Hoff

who had noted in 1884 that Vant Hoffs equation for

the temperature dependence of equilibrium constants

suggests such a formula for the rates of both forward

and reverse reactions. Arrhenius provided a physical

justification and interpretation for the formula.

Currently, it is best seen as an empirical relationship

and can be used to model the temperature variation of

diffusion coefficients, population of crystal

vacancies, creep rates, and many other thermally-

induced processes or reactions. [7]

MATERIALS AND METHODS

A.

Compounds TestedAspirin has the chemical formula C9H8O4 and the

IUPAC name 2-(acetyloxy) benzoic acid. It has the

molecular weight of 180.16g/mol. It has a density of

1.40g/cm3and a melting point of 136oC. [5]

B.

Procedure

1.

Preparation of Standard Solutions

20 mg of salicylic acid was weighed accurately and

was transferred into a 100mL volumetric flask. The

volume was filled with distilled water. (Stock

solution) 20mL from stock solution was transferredto a 50mL volumetric flask and was diluted to

volume. It was labeled as Solution A. Another 20mL

from the stock solution to a 100mL volumetric flask

and, again, was diluted to volume. It was labeled as

Solution B. Next, 20mL from Solution A was

transferred to a 50mL volumetric flask and was

diluted to volume. It was labeled as Solution C. 20mL

from Solution A was transferred to a 100mL

volumetric flask and was diluted to volume. It was

labeled Solution D. 20 mL from Solution C was

transferred to a 50mL volumetric flask and was

diluted. It was labeled as Solution E.

2.

Preparation of the Standard AbsorbanceConcentration Curve

Absorbance reading of the prepared standard

solutions were determined at 296nm using the UV-

vis spectrophotometer. The absorbance values were

plotted against the known Salicylic acid

concentration. Linear regression was used to obtain

the best fit line.

3. Preparation of Sample Solutions

40mg of Aspirin was weighed and transferred into a500mL volumetric flask. Volume was filled using

distilled water. Enough samples were taken and

subjected to absorbance reading at 296nm. 100mL of

the solution was transferred into 4 separate beakers

and was placed in ovens set at 50C.

4.

Preparation of Sample Solutions

Enough samples were gotten at 15, 30, 45, 60, 90,

and 120 minutes. The absorbance reading for each

sample was taken at 296nm. The concentration of

Aspirin remaining was determined based on thestandard absorbance-concentration curve. Log C of

the Aspirin vs. the remaining time was plotted. Then,

the degradation rate constant (k) of Aspirin was

determined for each temperature setting. Log k vs.

1/T was plotted. Using the Arrhenius equation, the

degradation rate constant at 25C was calculated.

RESULTS AND DISCUSSION

The experiment was conducted with a barometric

pressure of 74.7cmHg and a room temperature of

25.6oC.

Upon calculation of the concentration of each

solution prepared, the following values were obtained

(Table 1). Absorbance readings of each of the

prepared solution were done at 296nm using the UV-

VIS spectrophotometer and results can be seen

below.


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Computation for the concentration of each solution

follows the formula C1V1=C2V2as seen below.

Stock Solution= 0.20mg/mL

Solution A

C1V1=C2V2

0.20mg/mL (20mL) =C2(50mL)

C2=0.08mg/mL

Solution B

C1V1=C2V2

0.20mg/mL (20mL) =C2(100mL)

C2=0.04mg/mL

Solution C

C1V1=C2V2

0.08mg/mL (20mL) =C2(50mL)

C2=0.032mg/mL

Solution D

C1V1=C2V2

0.08mg/mL (20mL) =C2(100mL)C2=0.016mg/mL

Solution E

C1V1=C2V2

0.032mg/mL (20mL) =C2(50mL)

C2=0.013mg/mL

The a and b values were obtained after performing

linear regression in a calculator using the stat

function.

In graph form, here are the results.

Graph 1.Standard concentration absorbance curve

The concentration of aspirin solution was obtained by

computation. The absorbance reading was 1.167.

40mg/500mL = 0.08mg/mL

In order to obtain the concentration of salicylic acid

remaining as time passes at a temperature of 50oC,

the linear regression equation was utilized. The

tabulated results can be seen in Table 2.

y = bx + a

Where y = absorbance of sample

b = best fit line from standard solutions

a = a value from standard solutions

x = concentration of salicylic acid remaining

15 minsy = bx + a

0.986 = 14.32x + 1.06

x = -5.447X10-3mg

30 mins

y = bx + a

1.002 = 14.32x + 1.06

x = -4.3297X10-3mg

45 mins

y = bx + a

1.022 = 14.32x + 1.06

x = -2.933X10-3mg

60 minsy = bx + a

1.025 = 14.32x + 1.06

x = -2.723X10-3mg

90 mins

y = bx + a

1.030 = 14.32x + 1.06

x = -2.374X10-3mg

The concentration of acetylsalicylic acid remaining

as time passes at 50oC is taken from the computed

concentration of aspirin and the computed

concentration of salicylic acid, using the formula:

conc. of ASA = original conc. ASASA remaining

15 mins


x = 0.08 - (-5.447X10-3)

x = 0.085447 mg30 mins


x = 0.08(-4.3297X10-3)

x = 0.0843297 mg

45 mins


x = 0.08(-2.933X10-3)

x = 0.082933 mg

60 mins


x = 0.08(-2.723X10-3)

x = 0.082723 mg90 mins


x = 0.08(-2.374X10-3)

x = 0.082374 mg

The logarithmic equivalent of each value is taken in

order to plot the data in a graph. Using the formula:


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x = log (conc. of ASA)

15 mins


x = log (0.085447)

x = -1.0683

30 minsx = log (conc. of ASA)

x = log (0.0843297)

x = -1.0740

45 mins


x = log (0.082933)

x = -1.0813

60 mins


x = log (0.082723)

x = -1.0824

90 minsx = log (conc. of ASA)

x = log (0.082374)

x = -1.0842

The a and b values were obtained after performing

linear regression in a calculator using the stat

function.

Graph 2.Log concentration of aspirin vs. time graph

Using Arrhenius equation, the degradation rate

constant at 25oC was found as well as the half-life of

the drug and its shelf life.

Where k2 = degradation rate constant at T2

k1 = degradation rate constant at T1Ea = activation energy

R = gas constant

T1 = first temperature

T2 = second temperature

The degradation rate constant at 25oC is

3.35x10-5/min.

For the computation of half-life, the following

formula is used:

The half-life of the drug is at 14 days, 8 hours and 47

minutes.

In the computation of shelf-life, the following

formula is used:

The shelf life of the drug is at 2 days, 4 hours and 14

minutes.


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CONCLUSION

Shelf-life is the time required for 10% of the drug to

degrade and 90% of the drug to remain intact. The

computed value for aspirin at 25oC is 2 days, 4 hours

and 14 minutes. Half-life is the time required for 50%

of the drug to degrade and 50% of the drug to remain

intact. The computed value for aspirin at 25oC is 14

days, 8 hours and 47 minutes.

REFERENCES

[1] Bayquen, A., et. al. (2009). Synthesis of

Acetylsalicylic Acid (Aspirin). InLaboratory

Manual in Organic Chemistry(p. 141). Quezon City,

Philippines: C & E Publishing.

[2] https://pharmahub.org/resources/535/download/

ASA_Freshman_Lab_Handout.pdf

[3]http://en.wikipedia.org/wiki/Aspirin

[4] Yoshioka, S., et. Al (2000). Stability of Drugs andDosage Form. Springer Science and Business Media.

[5]http://en.wikipedia.org/wiki/Aspirin

[6]

http://en.wikipedia.org/wiki/Ultraviolet%E2%

80%93visible_spectroscopy

[7]http://en.wikipedia.org/wiki/Arrhenius_equation

[8] http://en.wikipedia.org/wiki/Half-life
http://en.wikipedia.org/wiki/Aspirinhttp://en.wikipedia.org/wiki/Aspirinhttp://en.wikipedia.org/wiki/Arrhenius_equationhttp://en.wikipedia.org/wiki/Arrhenius_equationhttp://en.wikipedia.org/wiki/Aspirinhttp://en.wikipedia.org/wiki/Aspirin

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Shelf Life Determination