Page 21 - Pharmaceutical Analytical Chemistry III

Example Proportional Error

Analyzing sample with impurities: (1) Analyte conc is 50 ppm
(true value), calculated amount is 55 ppm.

(2) Analyte conc is 500 ppm (true value), calculated amount is
550 ppm
For first case,
Absolute error = 55-50= 5 ppm
Relative Error (%Er) = (5 / 50) × 100 = 10%
For second case,
Absolute error = 550-500= 50 ppm
Relative Error (%Er) = (50 / 500) × 100 = 10%

relative error is constant