Pharmaceutical Analysis

gas-solid chromatography. Comprises all gas chromatographic methods in which the stationary phase is an active solid (e.g. charcoal, molecular sieves). Separation is achieved by adsorption of the components of a sample. 

Gel filtration is a technique of partition chromatography in which the partitioning  is based on the molecular size of the substances to be separated . In Gel Filtration chromatography, the stationary phase consists of porous beads with a well-defined range of pore sizes . proteins that are too large to fit inside any of the pores are said to be excluded .They have access only to the mobile phase between the beads and, therefore,elute first.

Gel permeation chromatography is a type of size exclusion chromatography, that separates analytes on the basis of size. This technique is generally used for the analysis of ploymer

steady changes of the mobile phase composition during chromatographic run is called gradient elution .The main purpose of the gradient elution is to move strongly retained components of the mixture faster but having least retained  component well resolved.