Spectroscopy is the study of how light interacts with matter and subsequently, spectrophotometry works thanks to the fact that light gets absorbed by matter. When a light passes through a solution, some of it will get absorbed in this manner. The higher the concentration of the substance in the solution, the more light will get absorbed and the less light gets transmitted through the solution or in other words, the less light will shine through.
It gives us an absorption spectrum which shows us how much light and at which wavelength gets absorbed by our sample. On the y-axis, the absorbance is displayed and on the x-axis, the different wavelengths. Where peaks occur, not as much light is reaching the detector, or in other words, light of these particular wavelengths get absorbed. In addition to this spectrum, most photospectrometers give the absorbance value as just a number. This is what we use to calculate the concentration of the sample solution.
To calculate the specific concentration of the solution used in the spectrometer, we use Beer’s law: $A = ebc$, A = absorbance, e = molar absorptivity, b = path length, c = concentration.
So why is this useful? Well as we just demonstrated together spectrophotometry can be used to quantify the amount of a certain substance in a solution. In addition it is especially useful when we want to measure the change in concentration of a solution over time. It is widely used in chemistry, physics, biology, biochemistry as well as material and chemical engineering…