A random sample of aspirin tablets Is taken for analysis of salicylic acid, an i

Question

A random sample of aspirin tablets Is taken for analysis of salicylic acid, an impurity which causes stomach inflammation. Each tablet contains about 5.0 mg with a pill-to- pill standard deviation of 0.20 mg or a 4.0% relative standard deviation. A single determination using a fluorescence method exhibits a relative standard deviation of 2.0% in the measurement step alone. Calculate relative standard deviation of the results of the following schemes: (a) Run a single determination on one pill (b) Analyze each of 10 pills separately and average the 10 determinations. (c) Mix together 10 pills; run a single determination on 1/10 of the pool. (d) Mix together 10 pills; run a determination on 1/10th portion; repeat the entire procedure 10 times and average the 10 results (consume 100 pills total but make only 10 determinations).

Explanation / Answer

given data:-

total contain in one tablet=5mg

standard deviation(s)=0.2mg or 4%

lets say the total number pills be x

que. run a single determination on one pill

ans. as given std deviation is 0.2 mg

i.e 5+0.2mg or 5-0.2mg

R.S.D=100*s/x

R.S.D=100*0.2/5

=4%

now a single determination by fluorescence method

by this method R.S.D is given 2% i.s 0.1 mg

R.S.D=100*s/x

5=100*s/5

s=0.1

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