**4. Conclusion**

Liquid chromatographic techniques have been widely used in pharmaceutical and clinical laboratories. Reversed phase, ion exchange, size exclusion and normal phase chromatogra‐ phy are commonly used types of these techniques. Affinity chromatography which provides analysis of bioactive molecules based on their biological functions or individual struc‐ tures has become increasingly important as another liquid chromatography technique [1,12]. Affinity chromatography is based on the simple principle that every biomolecule recog‐ nize another natural or artificial molecule such as enzyme and substrate or antibody and antigen [2,7]. In fact this technique is one of the oldest forms of liquid chromatography method [8]. The first use may be considered as the isolation of α-amylase by using an insoluble substrate, starch, in 1910 just three years after the discovery of chromatography by Tsewett [6,9]. The modern applications have started since 1960s with the creation of beaded agarose supports and the use of cyanogens bromide immobilization method. Since then, affinity chromatography has been gaining attention as a widely applicable techni‐ que for discovering the target proteins for bioactive compounds [3]. Up to the present time many different types of target proteins for bioactive compounds have been isolated and identified by affinity chromatography [21]. Today affinity chromatography is utilized as a valuable technique for the separation, purification and analysis of compounds present in complex samples and used in biochemistry, pharmaceutical science, clinical chemistry and environmental sciences. Application of affinity chromatography has significant advantag‐ es. The important one is that affinity chromatography involves many types of interac‐ tions between ligand and target such as steric effects, hydrogen bonding, ionic interactions, van der Waals forces, dipol-dipol interactions and even covalent bonds while other chromatographic techniques involve just one or a few of them. The combination of these multiple interactions leads to separation with high selectivity and retention in affinity chromatography [8]. However there are also several drawbacks in affinity chromatogra‐ phy system, such as non-specific binding of irrelevant proteins during affinity purifica‐ tion and chemical modification of bioactive compounds of interest used as ligands. These drawbacks limit its extensive application. After the completion of the Human Genome Project drug discovery research has focused on an approach that includes identification and characterization of molecular and cellular functions of a wide variety of proteins encoded by genomes. Thus, bioactive compounds become more important not only as therapeutic agents to treat diseases and disorders but also as useful chemical tools to examine their complex biological processes in vitro and in vivo [30]. Affinity chromatography which allows explaining the mechanism of action of bioactive compounds that are used as pharmaceutical drugs and biologically active natural products, therefore, has also signifi‐ cant importance in modern drug discovery [30].
