Page 22 - Quality control of pharmaceuticals (07-PA 704)

If the sample size is small, relative error is large.

Example Constant Error
1- The effect of solubility losses: solubility loss of 0.5 mg of a

precipitate,
A precipitate of weight of 500 mg,

Absolute error = 499.5-500= - 0.5 mg
Relative Error = (– 0.5 / 500) × 100 = – 0.1%
A precipitate of weight of 50 mg,

Absolute error = 49.5-50= - 0.5 mg
Relative Error = (– 0.5 / 50) × 100 = – 1%
If the ppt amount is small, relative error is large

The Effect of Determinate Errors Upon Analytical Results
Proportional Errors:
They increase or decrease is proportional to the size of the sample.
Absolute error varies with size of sample.
Relative error is constant, equally significant for all values of

measurement.
Example: Presence of an interfering impurity in sample, the amount of an
interferent increases with the size of the sample.
The determination of Cu2+ iodometrically, if the sample contain