Cation-exchange columns applications

The applicability of induced pH gradients for separation of metal ions within anion- and cation-exchange columns was verified. 

A good general-purpose weak acid cation-exchange column for non-suppressed applications is the Metrosep Cation C 2 column from Metrohm. As the selection of eluents used with this column is quite varied, the reader is referred to Metrohm column literature for specific eluent recommendations. The Metrosep Cation C 2 column is prepared via encapsulation of a porous silica substrate maliec acid copolymer. 

Another valuable application of ion-exchange resins involves concentrating ions from a very dilute solution. Thus, traces of metallic elements in large volumes of natural waters can be collected on a cation-exchange column and subsequently liberated from the resin by treatment with a small volume of an acidic solution the result is a considerably more concentrated solution for analysis by atomic absorption or ICP emission spectrometry (see Chapter 28). 

The successful application of 5-sulfosalicylic acid in ion exchange separations was demonstrated by Fritz and Palmer [15]. At an appropriate pH, they found that alumi-num(III), iron(III), uranium(VI), and vanadium(IV) are complexed and pass quickly through a cation exchange column. A number of other cations, including the rare earths, are not complexed and are retained on the column. Their application was simply a group separation, and no chromatographic separation of individual metal ions was involved. 

FIGURE 28-24 Typical applications of ion chromatography. (a) Separation of anions on an anion-exchartge column. Eluent 0.0028 M NaHCOj to 0.0023 M Na2C03. Sample size 50 pL. (b) Separation of alkaline earth ions on a cation-exchange column. EluenI 0,025 M phenylene-diamine dthydrochlohde to 0,0025 M HCI. Sample size 100 mL, (Couriesy of Dionex Corp., Sunnyvale, CA.)... 

The central and most essential part of an IC system is the separation column, and its stationary phase. The number of commercially available ion-exchange columns that have been developed for ion chromatography has increased impressively. The diversity of anion- and cation-exchange columns available today allows the ion chromatography user selection of stationary phase that is best suited for the required application. Nevertheless, the potential of packing and stationary phase design and development has not been explored to the full extent. 

Since the oxidation of thiols at mercury electrodes is facile and specific, it should be adaptable to HPLC detection. Rabenstein and Saetre" first reported this and so gave rise to a significant improvement in the assay of thiols in complex mixtures. Cysteine and other amino-thiols were separated on a cation-exchange column and detected at a mercury-pool EC detector (-1-0.05 V vs SCE) with a sensitivity of < 1 nmol for most of the thiols tested. Sample preparation consisted of little more than diluting a protein-free extract of a biolluid. These authors subsequently detailed many applications of this assay, e.g. D-penicillamine in blood and urine, cysteine and homocysteine in plasma and urine" and cysteine and glutathione in... 

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