FAQs on Analysis with Ion Exchange Chromatography

Which ion-exchange chemistries do you offer for HPLC columns?

Polymer-based columns: Weak and strong anion and cation exchangers are available. These columns are designed with 100 nm pore size and various column sizes ranging from analytical to semi-preparative scale.

Table 1: Functional groups available on TSKgel ion exchange columns

Functional group	Cation-exchange	Anion-exchange
Weak	Carboxymethyl	Diethylaminoethyl
Strong	Sulfopropyl	Quarternary ammonium

Also available are BioAssist Q (a polyamine anion exchanger) and BioAssist S (a sulfopropyl cation exchanger), both are very large pore size, high capacity, ion exchangers.

Silica-based columns: Weak and strong anion and cation exchangers are available. These columns are designed with 12.5 nm (upper molecular weight limit of 10 kDa) and 25 nm (upper molecular weight limit 30 kDa) pore sizes.

Specialty columns: Cation and anion exchange ligands are attached to a polystyrene-divinylbenzene (PS-DVB) polymeric support. These are used for the separation of carbohydrates, amino acids and, organic acids.

Do I need anion-exchange or cation-exchange?

Whether an anion- or cation-exchanger is suited for the separation depends on the isoelectric point of the analyzed molecule and on the pH at which analysis occurs. Anion-exchange separates negatively charged molecules. A molecule is negatively charged if it is present at a pH above its isoelectric point. For separations at pH 7 the molecule is negatively charged if the isoelectric point (pI) is lower than 7. The opposite is true for cation-exchange: it separates positively charged molecules. A positive charge is present if a molecule is analyzed at a pH below its isoelectric point, for a pH of 7 for analysis this means the molecule has a pI higher 7.

What is the difference between strong and weak ion exchange columns?

The terms weak and strong ion exchanger refer to the sensitivity of the ionization of ligands to pH changes. Strong ion exchangers are ionized over a broad range of pH values whereas weak ion exchangers have only a narrow range. This means the amount of charges present to interact with a charged molecule changes with pH. Strong ion exchangers are less susceptible to pH changes and are regarded to be easier for method development, whereas weak anion exchangers provide more possibilities to adjust their selectivity by pH changes.

What is the difference between TSKgel columns DNA-NPR and DNA-STAT?

DNA-NPR and DNA-STAT columns share their suitability for analyzing nucleic acid-based molecules and their non-porous base matrices. However, they differ in the following characteristics:

Table 2: Difference between DNA-NPR and DNA-STAT column

	Particle size	Dimensions	Ligand	Application
DNA-NPR	2.5 µm	4.6 mm ID x 7.5 cm L	DEAE	For very low sample amounts and fastest analyses
DNA-STAT	5 µm	4.6 mm ID x 10 cm L	Q	Higher binding capacity à for higher sample amounts

What is the difference between TSKgel columns DNA-NPR and DEAE-NPR?

DNA-NPR and DEAE-NPR columns are both weak anion exchange columns with a particle size of 2.5 µm, they differ in the following characteristics:

Table 3: Difference between DNA-NPR and DEAE-NPR column

	Dimensions	Ligand	Quality control	Shipping solvent	Application
DNA-NPR	4.6 mm ID x 7.5 cm L	DEAE	Nucleotide-based	20 mM Tris-HclO4 with 38 mM NaClO4 (pH 9).	DNA, RNA, Oligonucleotides
DEAE-NPR	4.6 mm ID x 3.5 cm L	DEAE	Protein-based	Water	Proteins