Colorimetry is an analytical technique used in inorganic analysis to determine the concentration of a substance in a solution based on the intensity of its color. It is especially useful for metal ions that form colored solutions or complexes.
Principle:
- Many inorganic ions or their complexes absorb light of a specific wavelength.
- The intensity of the color is proportional to the concentration of the substance in the solution.
- By measuring how much light is absorbed using a colorimeter, the concentration of the analyte can be calculated using Beer’s Law (absorbance is proportional to concentration).
Procedure:
- Prepare the sample solution containing the colored ion or complex.
- Select a wavelength of light that the solution absorbs strongly.
- Measure the absorbance using a colorimeter.
- Compare the absorbance with a calibration curve prepared from standard solutions of known concentration.
- Determine the concentration of the unknown solution from the calibration curve.
Applications:
- Estimation of metal ions like iron, copper, chromium, and cobalt.
- Determination of complex formation in solution.
- Environmental analysis, e.g., measuring nitrate or phosphate concentrations in water.
- Quality control in industrial and pharmaceutical samples.
Advantages:
- Simple, fast, and sensitive.
- Requires only small amounts of the sample.
- Can detect ions in very low concentrations.
Limitations:
- Only works for colored ions or complexes.
- Interference from other colored substances can affect accuracy.