The three major groups of chromatographic techniques are gas chromatography (GC), high-performance liquid chromatography (HPLC), and electrophoretic techniques, which differ in the applied mobile phase (gas or liquid) and in the type of retention and flow mechanism. GC is used for the separation of volatile compounds. Thus, it is useful for determination of low-molecular-weight compounds (below 500 Da) but cannot be used for large, highly polar, or thermally labile compounds. Implementation of GC is simple and routine. GC is mostly coupled with flame ionization detection (FID), electron capture detection (ECD), or mass spectrometry (MS). HPLC is used for nonvolatile compounds and is well suited for the analysis of low- and high-molecular weight compounds such as peptides and proteins. HPLC is mostly coupled with ultraviolet visible (UV-VIS) wavelength spectroscopy or mass spectrometric detection. Electrophoretic techniques are used for nonvolatile compounds, which are permanently or temporarily charged, such as proteins or organic salts. Electrophoretic techniques have an increasing importance in biomedical fields, such as proteomics. Chromatographic techniques help in ensuring the selectivity and sensitivity necessary for clinical analysis, and contribute to the success of the analytical process. Complete separation in biological samples is rarely feasible. The purpose is more often to reduce the complexity of a mixture, enrichment of a given component, or removal of interferences.
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