Liquid chromatography (HPLC) is a column chromatography technique that utilizes a liquid solvent as the  phase and employs a finely divided solid stationary phase for separation. Compared to gas chromatography, liquid chromatography offers broader applicability, as it is not limited by the volatility and thermal stability of the analytes, thereby compensating for the limitations of gas chromatography. Approximately 20% of known organic compounds can be analyzed using gas chromatography, while the remaining 80% require liquid chromatography.

The process of liquid chromatography analysis is as follows: Firstly, the solvent is drawn from the reservoir bottle into the chromatographic system using a pump, and then it is delivered and introduced into the injector after flow rate and pressure measurements. The sample of interest is injected into the system via the injector and carried by the liquid phase through the chromatographic column, where separation takes place, before reaching the detector. The detection signal is collected by data processing equipment, processed, and used to generate a chromatogram. The waste liquid is collected in a waste container.

For the separation of complex mixtures, liquid chromatography can utilize a gradient controller to perform gradient elution. This process is similar to the temperature program used in gas chromatography, except that in liquid chromatography, the properties of the liquid phase are modified to achieve optimal separation of the sample components.

Liquid chromatography finds wide applications in various fields:

Environmental field: Used for the analysis of common inorganic ions, polycyclic aromatic hydrocarbons, polychlorinated biphenyls, nitro compounds, harmful heavy metals and their species, herbicides, pesticides, acid deposition components, etc.

Agricultural field: Used for the analysis of soil mineral composition, fertilizers, feed additives, organic and inorganic components in agricultural products such as tea.

Petroleum field: Used for the analysis of hydrocarbon composition and trace components in petroleum.

Chemical industry field: Used for the analysis of inorganic chemical products, synthetic molecular compounds, surfactants, detergent components, cosmetics, dyes, etc.

Materials field: Used for the analysis of liquid crystal materials, synthetic molecular materials, etc.

Food field: Used for the analysis of inorganic ions, organic acids, amino acids, sugars, vitamins, fatty acids, flavors, sweeteners, preservatives, artificial colors, pathogenic microorganisms, mycotoxins, polycyclic aromatic hydrocarbons, and other food components.

Biological field: Used for the analysis of amino acids, peptides, proteins, nucleic acids, biogenic amines, polysaccharides, enzymes, natural molecular compounds, etc.

Pharmaceutical field: Used for the analysis of human body chemical components, various synthetic drug components, chemical components of various natural plant and animal medicines, etc.