In spectrophotometry, absorbance is measured by finding out how much light a sample absorbs when light passes through it.
Here’s how it works, step by step:
1. Light Source
- The spectrophotometer shines a beam of light onto the sample.
- The light passes through a monochromator, which selects one specific wavelength.
2. Passing Through the Sample
- The light goes through a cuvette containing the sample solution.
- Some light is absorbed by the sample, and the rest passes through.
3. Detector Measurement
- A detector measures how much light comes out of the sample.
- It also measures how much light went in (the reference or blank).
4. Calculation
- The instrument compares the light intensity before (I₀) and after (I) it passes through the sample.
- It then calculates absorbance (A) using the relationship between these two values.
5. Display of Results
- The absorbance value is shown on the screen.
- Higher absorbance means more light was absorbed — and usually, a higher concentration of the substance.
In short:
Absorbance is measured by shining light through a sample and seeing how much of that light is absorbed compared to the light that entered.
Less light coming out means higher absorbance.