How to use a spectrometer?

### PRINCIPLE

The measurement is based on the use of Beer-Lambert’s law: $\large A = \log \frac {I_{0}}{I} = \varepsilon \cdot L \cdot C$

It includes two steps:

1. Finding ε: this is the calibration stage. In practice, the length L is fixed by the cuvettes in which the absorbance is measured. The absorbance measurement of several solutions with different concentrations gives a range of values Ai and Ci that allow to draw the graph, which is generally linear. Its slope is ε x L.
2. Counter-calibration: the absorbance measurement gives a value Ax which leads to the concentration Cx after graphical analysis based on the calibration curve.
Both steps use measurements of A that are detailed in the following protocol: