Spectrophotometry is a useful and widely used technique, but it has some limitations. Here’s a explanation:
1. Interference from Other Substances
- If the sample contains other compounds that absorb light at the same wavelength, it can give inaccurate results.
- Purity of the sample is important.
2. Limited Sensitivity
- Spectrophotometry may not detect very low concentrations of a substance.
- For trace analysis, more sensitive techniques like fluorometry or mass spectrometry may be needed.
3. Requires Clear Solutions
- Turbid, colored, or particulate samples can scatter light, affecting measurements.
4. Narrow Linear Range
- The relationship between absorbance and concentration (Beer-Lambert law) holds only for a limited concentration range.
- Too high or too low concentrations can give non-linear results.
5. Solvent Effects
- Some solvents absorb light themselves, interfering with the measurement.
6. Limited Structural Information
- Spectrophotometry gives quantitative data, but provides little or no information about chemical structure.
7. Temperature and Instrument Factors
- Changes in temperature, lamp intensity, or stray light can affect accuracy.
In short:
Spectrophotometry is simple and fast, but it is limited by interferences, low sensitivity, sample clarity, narrow linear range, solvent effects, and lack of structural information. Proper sample preparation and method control are essential to get reliable results.