High-Performance Liquid Chromatography (HPLC) is a sophisticated analytical technique widely used in environmental chemistry for separating, identifying, and quantifying components in complex mixtures. The underlying principle of HPLC is based on the differential partitioning of analytes between a mobile phase and a stationary phase. The mobile phase, usually a liquid solvent or a mixture of solvents, carries the sample through a column packed with the stationary phase, which is typically composed of finely divided particles with specific chemical properties. Components in the sample interact differently with the stationary phase depending on their polarity, size, or affinity, resulting in their separation as they travel through the column at varying rates. The separation can be further influenced by the composition, pH, and flow rate of the mobile phase, as well as the nature and particle size of the stationary phase. HPLC systems generally consist of several essential components designed to achieve precise and reproducible separation. The first component is the solvent reservoir, which contains the mobile phase. The choice of solvent or solvent mixture is crucial, as it must adequately dissolve the sample and interact optimally with the stationary phase. The mobile phase is then delivered through the system by a high-pressure pump, which maintains a constant flow rate, typically in the range of milliliters per minute. Modern HPLC pumps can generate pressures up to 6000 psi or more, which is necessary to push the solvent through densely packed columns efficiently. A sample injector or autosampler introduces a precise volume of the sample into the mobile phase stream, ensuring reproducibility and minimizing human error. The column, which is the heart of the system, contains the stationary phase and is often maintained at controlled temperatures to enhance resolution and reproducibility. The detection system in HPLC is critical for monitoring the separated analytes as they elute from the column. Several types of detectors are commonly employed, depending on the chemical nature of the analytes and the sensitivity required. Ultraviolet-visible (UV-Vis) absorbance detectors are widely used due to their simplicity, versatility, and ability to detect compounds with chromophores. Fluorescence detectors offer higher sensitivity for compounds that naturally fluoresce or can be derivatized to fluoresce. Refractive index detectors measure changes in the refractive index of the eluent and are suitable for analytes lacking UV absorbance. More advanced detectors, such as mass spectrometers (HPLC-MS), provide structural information and extremely high sensitivity, making them invaluable in trace environmental analysis. Data from the detector are processed and displayed as a chromatogram, where peaks represent individual analytes. Retention times, peak areas, and peak heights are used for qualitative and quantitative analyses. Environmental applications of HPLC are vast due to its