Analysis of a single analyte and purity control

In practice, the first step is the construction of a calibration curve A = f (c) from solutions of known concentration of the compound to be measured, submitted to the same treatment as the sample. This curve, which is most often a straight line for dilute solutions, allows determination of the concentration of the unknown sample. 

Calculation of the concentration of an analyte by expression 9.13 leads to an erroneous result if the sample contains an impurity (absent in the reference solution) which also absorbs at the wavelength of measurement. Therefore a method commonly named confirmatory analysis is used. 

---