9780521516358book.pdf

strong exchangersbecause they are totally ionised at all normal working pH values,

and carboxylate (–COO) and diethylammonium (–HNþ(CH 2 CH 3 ) 2 ), both of which are

termedweak exchangersbecause they are ionised over only a narrow range of pH

values. Examples are given in Table 11.3. Bonded phase ion exchangers suitable for

HPLC, containing a wide range of ionic groups, are commercially available. Porous

varieties are based on polystyrene, porous silica or hydrophilic polyethers, and are

particularly valuable for the separation of proteins. They have a particle diameter

of 5 25 mm. Most HPLC ion exchangers are stable up to 60C and separations are

often carried out at this temperature, owing to the fact that the raised temperature

Table 11.3Examples of commonly used ion exchangers

Type

Functional

groups

Functional

group name Matrices

Weakly acidic (cation exchanger)COO– Carboxy Agarose

CH 2 COO– Carboxymethyl Cellulose

Dextran

Polyacrylate

Strongly acidic (cation exchanger)SO 3 Sulpho Cellulose

CH 2 SO 3 Sulphomethyl Dextran

CH 2 CH 2 CH 2 SO 3 Sulphopropyl Polystyrene

Polyacrylate

Weakly basic (anion exchanger) CH 2 CH 2 NþH 3 Aminoethyl Agarose

CH 2 CH 2 NþH

j

(CH 2 CH 3 ) 2

Diethylaminoethyl Cellulose

Dextran

Polystyrene

Polyacrylate

Strongly basic (anion exchanger)CH 2 Nþ(CH 3 ) 3 Trimethylaminomethyl Cellulose

CH 2 CH 2 Nþ(CH 2 CH 3 ) 3 Triethylaminoethyl Dextran

CH 2 Nþ(CH 3 ) 2

j

CH 2 CH 2 OH

Dimethyl-2-hydroxyethyl-

aminomethyl

Polystyrene

CH 2 CH 2 Nþ(CH 2 CH 3 ) 2

j

CH 2 CH(OH)CH 3

Diethyl-2-hydroxypropyl-

aminoethyl

460 Chromatographic techniques