Cation exchange elution order

Paris (1967) studied the elution of rare earths, on a-hydroxyisobutyrate-charged Dowex 1-X4, with 0.0125 M aHIB in 25% aqueous methanol (propanol, ethanol, isopropanol, tetrahydrofuran, acetone, cellosolve, dioxane, etc.). The elution order was La-Ce-Pr-Nd-Sm-Eu-Gd-Tb-Dy-Ho-Er-Tm-Yb-Lu. .. the reverse of that observed in cation-exchange elution experiments with aHIB. Yttrium eluted with Dy. Erom the distribution data, the individual separation factors appear to diminish from about 2.8 for La-Ce to about 1.1 for Yb-Lu. 

Ion-exchange separations can also be made by the use of a polymer with exchangeable anions in this case, the lanthanide or actinide elements must be initially present as complex ions (11,12). The anion-exchange resins Dowex-1 (a copolymer of styrene and divinylben2ene with quaternary ammonium groups) and Amherlite IRA-400 (a quaternary ammonium polystyrene) have been used successfully. The order of elution is often the reverse of that from cationic-exchange resins. 

In order to remove the residual PME the AE fraction was further fractionated on Mono S cation exchange column. Unlike the DEAE-Sepharose column, where PME elutes after the AE activity, the order of elution was reversed on the Mono S column (Fig. 1). The last step in the purification was a gel filtration (Sephacryl S-200) column. 

For sufficient retention of these very polar sulfonated carboxylates on RP columns, the addition of an ion-pairing (IP) agent such as tetraethylammonium acetate (TEAA) to the LC buffer was compulsory [13]. To maintain the compatibility of the eluent with the MS interface, the use of such an involatile cationic additive entailed a cation exchanger to be placed between the column and the interface [13]. Alternatively, equimolar amounts (5 mM) of acetic acid and triethyl-amine, which form the volatile IP agent triethylammonium, were added to the mobile phase in order to improve the retardation of very polar SPC [14]. While the first approach with TEAA was effective in retaining even the very short-chain C3- and C4-SPC (Fig. 2.10.4), the weaker IP agent triethylammonium notably increased the retention of C5-SPC and higher, whereas C4-SPC elutes almost with the dead volume of the LC (Fig. 2.10.5). Addition of commonly used ammonium acetate as buffer component led to the co-elution of the short-chain SPC ([Pg.322]

The separation of the same charged compounds were also accomplished on an ethyl-pyridine bonded silica surface and 30 0% methanol/C02 mobile phases without the need of added sulfonate modifier. Anionic compounds did not elute from the ethyl-pyridinium surface that lead the authors to hypothesize that the surface was positively charged. To further test this hypothesis, the separation of the same compounds on a strong anion exchange column, silica-based propyltri-methylammonium cationic surface, which exhibits are permanent positive charge was attempted. The same retention order was observed on the strong cation exchange surface. 

El 1. Amino acid analyzers are instruments that automatically separate amino acids by cation-exchange chromatography. Predict the order of elution (first to last) for each of the following sets of amino acids at pH = 4. 

The separation of rare earths by anion exchange resins depends on somewhat different factors for a given chelating agent than to the cation exchange resins. For EDTA in an anion exchange process the order of elution is not the inverse order of the stability constants as in cation exchange process, rather [79] 4... 

The distribution coefficient increases from La3+ to Lu3+ and then decreases with increasing Z. When citrate ion is used as eluant the elution sequence is the reverse of the order for cation exchange resins [50]. 

Peptide Purification At pH 7.0, in what order would the following three peptides be eluted from a column filled with a cation-exchange polymer Their amino acid compositions are ... 

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