Pyridine is conventionally detected by the gas chromatography and mass spectrometry methods. Purification can be achieved by preparative chromatography. These chromatographic processes are known as periodic counter-current chromatography (PCC). There are distinct differences between displacement and elution chromatography. Phosphomolybdic acid is used as a reagent for staining phenolics in thin layer chromatography. HPLC is used for nonvolatile mixtures that would not be suitable for gas chromatography. I, delipidation, anion exchange chromatography, cation exchange chromatography, and gel filtration chromatography. Recombinant proteins need many operations involving ultrafiltration and column chromatography. Rotary valves are used for loading samples on columns used for liquid or gas chromatography. Such series are useful for determining necessary solvents needed for chromatography of chemical compounds. These can be separated by ion exchange chromatography. There are various methods, including crystallization, chromatography, and the use of enzymes. This is the immobilized metal ion affinity chromatography announced in 1975. It also does not reduce metals used in immobilized metal affinity chromatography. Instrumental techniques involving gas or liquid chromatography are usually employed for these purposes.