Infrared (IR) spectrometry and mass spectrometry are two pivotal analytical techniques in environmental chemistry, each providing unique insights into the composition, structure, and quantity of chemical species in environmental samples. Both techniques rely on fundamental principles of molecular interaction with energy, allowing scientists to identify pollutants, study chemical transformations, and monitor environmental quality. IR spectrometry is based on the principle that molecules absorb infrared radiation at specific frequencies corresponding to the vibrations of chemical bonds. When a molecule is irradiated with IR light, certain wavelengths are absorbed, leading to vibrational transitions within the molecule. Each functional group in a molecule, such as C=O, O-H, N-H, or C-H, absorbs IR radiation at characteristic frequencies, producing a spectrum that acts as a molecular fingerprint. The absorption of energy occurs because the IR radiation induces changes in the dipole moment of bonds, and these absorptions are detected as peaks in an IR spectrum. This makes IR spectrometry particularly useful for identifying functional groups and elucidating molecular structures. The instrumentation of IR spectrometry typically includes an IR source, a sample holder, a monochromator or interferometer, and a detector. The IR source emits radiation in the mid-infrared region (approximately 4000–400 cm⁻¹), which passes through the sample. The sample may be in the form of a gas, liquid, or solid, often prepared as a thin film or mixed with an IR-transparent matrix for solid samples. The monochromator or interferometer separates the radiation into its constituent frequencies, and the detector measures the intensity of transmitted or absorbed radiation. Modern Fourier-transform infrared (FTIR) spectrometers use an interferometer and computer algorithms to rapidly obtain high-resolution spectra with improved signal-to-noise ratios. In environmental applications, IR spectrometry is employed extensively to monitor air, water, and soil pollutants. It is particularly useful for detecting organic compounds, such as volatile organic compounds (VOCs), polycyclic aromatic hydrocarbons (PAHs), and pesticides, which have distinct IR absorption bands. For example, IR spectroscopy can identify carbonyl compounds, alcohols, or nitrates in contaminated water. In air quality monitoring, IR techniques are