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 separate 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

The relative standard deviation is calculated by the following formula: s/x * 100.

Single determination on one pill in measurement step = 2.0

Standard deviation in measurement step = 0.1

b.single determination on each of the 10 pills = 2.0

Single determination of average of analysis of 10 pills = 2.0.

c. Single determination of the mix of 10 pills = 2.0

d. Single determination of the required procedure = 2.0.

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