What is the principle behind the operation of a spectrophotometer?

The principle behind the operation of a spectrophotometer is the absorption of light by a solution. A spectrophotometer measures how much light of a specific wavelength is absorbed by the sample. When light passes through a solution, certain wavelengths of light may be absorbed by the molecules of that solution, depending on their electronic structure. This absorption corresponds to electronic transitions within the molecules and is unique to the specific compounds present in the solution.

By quantifying the amount of light absorbed at various wavelengths, a spectrophotometer can provide valuable information about the concentration of the absorbing species in the solution, following Beer-Lambert law. This law states that the absorbance is directly proportional to the concentration of the absorbing species and the path length of the light through the solution, allowing for quantitative analysis.

This operational principle distinguishes spectrophotometry from the mechanisms of reflection, refraction, and diffraction, which involve the bending, spreading, or bouncing of light rather than its absorption. Understanding the absorption of light is fundamental to interpreting spectrophotometric data and applying it in various chemical analyses.