Infrared (IR) spectrometry and mass spectrometry are two powerful analytical techniques widely employed in environmental chemistry to identify, quantify, and study the behavior of chemical substances in natural and polluted environments. Both methods rely on the interaction of matter with energy, but the nature of that energy differs, leading to unique principles, instrumentation, and applications. The principle of IR spectrometry is based on the absorption of infrared radiation by molecules, which causes vibrational transitions in chemical bonds. When a molecule is exposed to IR radiation, specific frequencies are absorbed corresponding to the vibrational energies of particular functional groups. Each type of chemical bond, such as C–H, O–H, N–H, or C=O, has characteristic absorption frequencies, and the resulting IR spectrum acts as a molecular fingerprint that can be used to identify compounds. The technique primarily provides qualitative information about the molecular structure and can also offer semi-quantitative data based on absorbance intensity. The instrumentation of IR spectrometry typically includes an IR radiation source, a sample holder or cell, a monochromator or interferometer, and a detector. The radiation source emits IR light that passes through the sample. In a dispersive IR spectrometer, a monochromator separates the light into its component wavelengths, while in a Fourier-transform IR (FTIR) spectrometer, an interferometer modulates the IR light, and a mathematical Fourier transformation generates the spectrum. The detector measures the transmitted or absorbed radiation, producing an absorption spectrum that shows peaks corresponding to various vibrational modes of the molecules. Modern FTIR instruments are highly sensitive, allowing rapid