Eluants for Anion Exchange Chromatography

1 mmol/L sodium acetate buffer (pH 5.6) + 0.05 mol/L NaCl04 flow rate 1 mL/min detection UV (214 nm) injection volume 2 pL solute concentrations 1 g/L each of iodide (1), nitrate (2). nitrite (3). bromate (4), and benzoate (5) (taken from [67]). 

The kind of eluant that is used for anion eiorhange chromatography depends mainly on the detection system being employed. Since the detection of inorganic and organic anions in many cases is performed with conductivity detection, the eluants used are classified into two groups  

Independently, the affinities of eluant ions and solute ions must be comparable i.e., as a rule of thumb, divalent solute ions may only be eluted with divalent eluant ions. 

The versatile mixture of sodium carbonate and sodium bicarbonate, on the other hand, finds widespread application, because the elution power and the selectivity resulting there from are determined solely by the concentration ratio of these two compounds. A great variety of inorganic and organic anions can be separated with this eluant combination. As the product of the suppressor reaction, the carbonic acid is only weakly dissociated, so that the background conductivity is very low. 

As an alternative to carbonate/bicarbonate systems, amino acids (a-aminocar-boxylic acids) may be used as an eluant [69, 70]. Their dissociation behavior is depicted in Fig. 3-66. At alkaline pH, amino acids exist in the anionic form due to the dissociation of the carboxyl group and, thus, may act as an eluant ion. 

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Eluants for Anion Exchange Chromatography 101 Table 3-10. Eluants commonly used for suppressed conductivity detection. 

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