How do spectral methods use electromagnetic radiation to analyze substances?

Spectral methods analyze substances by measuring the interaction between electromagnetic radiation and the energy levels of atoms or molecules. These methods rely on the principle that substances absorb or emit radiation at characteristic frequencies as they transition between quantized energy states.12

Mechanisms of Analysis

• Absorption: When a substance absorbs radiation, the frequency of the absorbed energy corresponds to the difference between two energy levels ($E_{hi}-E_{lo}=h\nu$). For example, infrared radiation causes specific vibrational and rotational changes in molecules, allowing for the identification of functional groups.13
• Emission: In emission spectroscopy, atoms are excited by energy sources like electrical discharges or flames. As these atoms return to lower energy states, they emit light at characteristic frequencies, which are then dispersed and measured to identify elemental composition.2

Quantitative and Qualitative Applications

By dispersing radiation into its component wavelengths using spectrometers, scientists can measure the intensity of light absorbed or emitted. The intensity is often proportional to the concentration of the substance, a principle utilized in techniques like colorimetry and atomic absorption spectrometry.425