Biochemical Techniques and Instrumentation

2.3.4. Ion exchanger support matrix

The support matrix are mainly made of cellulose, dextran, polyether, polystyrene, polyacrylate, agarose and silica. They have either an anionic or a cationic functional group derivatized to its surface. These two groups are further divided into weak and strong ion exchangers.

1. Weak Ion exchanger: Most common weak ion exchangers carry either the diethylaminoethyl (DEAE) or carboxymethyl (CM) groups derivatized to the support matrix. The former is an anion exchanger while the latter is a cation exchanger. Another weak anion exchanger is polyethyleneimine (PEI) which is used specifically to separate proteins and nucleic acids.
2. Strong Ion exchanger: Strong anion exchanger groups are quaternary aminoethyl (QAE), while strong cation exchangers carry sulfopropyl (SP) groups on their surface. These ion-exchange groups are fully ionized over a wide pH range.

Separation by adsorption of the molecule to the support matrix is preferable when several different molecules are to be separated. Separation by adsorption of the unwanted materials to the support matrix is preferable when single molecule is to be separated.

The different type of exchangers, their functional groups and the support matrix are given in the Table 2.3.1.

Type	Functional groups	Functional group name	Resins
Weakly acidic (cation exchanger)	-COO-	Carboxy	Agarose
	-CH2COO-	Carboxymethyl (CM)	Cellulose Dextran Polyacrylate
Strongly acidic (cation exchanger)	-SO3-	Sulpho	Cellulose
	-CH2SO3-	Sulphomethyl	Dextran
	-CH2CH2CH­ SO3-	Sulphopropyl	Polystrene, Polyacrylate
Weakly basic (anion exchanger)	-CH­2CH2N+H3	Aminoethyl	Agarose
	- CH­2CH2N+H I (CH2CH3)2	Diethylaminoethyl (DEAE)	Cellulose Dextran Polystyrene Polyacrylate
Strongly basic (anion exchanger)	- CH2N+(CH3)3	Trimethylaminomethyl	Cellulose
	- CH2CH2N+(CH2CH3)3	Triethylaminoethyl	Dextran
	- CH­2N+(CH3)2 I CH2CH2OH	Dimethyl – 2- hydroxyethyl - aminomethyl	Polystyrene