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GC can be divided into two categories: gassolid chromatography. In GSC, the mobile phase is a gas and the stationary phase is a solid that retains the analytes by adsorption.GSC is most suitable for low molecular weight gaseous species like nitrogen oxides and carbon dioxide.GLC is based upon partition of the analytes between an immobilized liquid and a gas phase.Several different liquid <a href="http://www.targetmol.com/compound/Vorinostat"></a> phases exist for GLC with a wide range of applications.This technique is suitable for all kinds of volatile analytes, such as steroids, alcohols, amino acids, fatty acids and sugars.Efficient separation of compounds in GC is dependent on the compounds travelling through the column at different rates.Longer columns are employed to obtain better separation.Column temperature, the polarityof the column, flow rate, and length of a column are supposed to be constant during analysis.For each planned GC experiment, these factors have been optimized to separate compounds. HPLC utilizes a column that holds chromatographic packing material through the column, and a detector that shows the retention times of the molecules.Retention time varies depending on the interactions between the stationary phase, the molecules being analyzed, and the solvent used.HILIC most often uses a bonded polar stationary phase and a nonpolar, water miscible, mobile phase.Partition HPLC has been used historically on unbonded silica or alumina   supports.Each works effectively for separating analytes by relative polar differences, however, HILIC has the advantage of separating acidic, basic and neutral solutes in a single chromatogram.The polar analytes diffuse into a stationary water layer associated with the polar stationary phase and are thus retained.Retention strengths increase with increased analyte polarity, and the interaction between the polar analyte and the polar stationary phase increases the elution time.The interaction strength depends on the functional groups in the analyte molecule which promote partitioning but can also include coulombic interaction and hydrogen donor capability.Use of more polar solvents in the mobile phase will decrease the retention time of the analytes, whereas more hydrophobic solvents tend to increase retention times.Partition and NPHPLC had fallen out of favor in the s with the development of reversedphase HPLC because of a lack of reproducibility of retention times as water or protic organic solvents changed the hydration state of the silica or alumina chromatographic media.Recently it has become useful again with the development of HILIC bonded phases which improve reproducibility.It was one of the first kinds of HPLC that chemists developed.NPHPLC uses a polar stationary phase and a nonpolar, nonaqueous mobile phase, and works effectively for separating analytes readily soluble in nonpolar solvents.The analyte associates with and is retained by the polar stationary phase.Adsorption strengths increase with increased analyte polarity, and the interaction between the polar analyte and the polar stationary phase increases the elution time.The interaction strength depends not only on the functional groups in the analyte molecule, but also on steric factors.The effect of sterics on interaction strength allows this method to resolve structural isomers.The use of more polar solvents in the mobile phase will decrease the retention time of the analytes, whereas more hydrophobic solvents tend to increase retention times.

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