Chromatographs

Chromatographs are analytical instruments that perform chromatography, a process for separating the components of a mixture as they are carried by a mobile phase through a column containing a stationary phase. Different compounds interact with the stationary phase to different extents, causing them to travel at different speeds and exit the column separately. The instrument's detector records a signal as each component arrives, producing a chromatogram, a plot of detector response versus time or volume. The resulting peaks are used to identify components and, with calibration, to estimate their concentrations.

The main categories are gas chromatography (GC) and liquid chromatography (LC). In GC the mobile phase is a gas and separating columns are typically capillary or packed with a stationary phase; common detectors include flame ionization, thermal conductivity, and mass spectrometry. LC uses liquids as the mobile phase and often employs high-performance liquid chromatography (HPLC) or ultra-high-performance LC; detectors include UV–visible, refractive index, and mass spectrometry. Modern systems integrate autosamplers, temperature-controlled ovens, multiple detectors, and advanced data-processing software.

Historically, the term chromatography was coined by Mikhail S. Tsvet in 1903, who used it to separate plant pigments and introduced the concept of a partitioning process between stationary and mobile phases. Today chromatographs are used across chemistry, biology, environmental science, medicine, and industry to separate, identify, and quantify components in complex mixtures.

Practical considerations include instrument maintenance (column life, detector calibration, carrier-gas purity) and method development to achieve adequate resolution. Limitations include method-specific selectivity, potential sample loss, and the need for standards for accurate quantification.