Cation exchange methanesulfonic eluent

Considerable interest has been shown in a novel cation exchanger first developed by Schomburg et. al. [43]. The material consists of a silica substrate of very uniform particle size coated with a poly(butadiene-maleic acid) resin which serves as the cation-exchange moiety. This material, which is now conunercially available, gives good separations of both monovalent and divalent metal ions in a single run. Ordinary eluents such as hydrochloric or methanesulfonic acid, or complexing eluents may be used [44,45]. 

Simultaneous analysis of alkali and alkaline earth metals can only be performed with weak acid cation exchangers, using carboxylic groups as ion-exchange functionality group and usually with methanesulfonic acid as the eluent. 

Later research has reafHrmed these early results [23]. A separation of alkali metal ions was first attempted in water alone using the lightly sulfonated macro-porous cation exchanger with aqueous 3 mM methanesulfonic acid as the eluent. Under these conditions the sample cations exhibited very similar retention times. The selectivity of the macroporous resin for alkali metal ions was improved con-... 

As discussed in the early part of this chapter, macro-cyclic complexes are generally more stable in nonaqueous solvents than in aqueous solution. Therefore, it is expected that adding 18-crown-6 to a nonaqueous mobile phase would increase the retention time of cations to be separated. Fritz s group added 18-crown-6 to a nonaqueous IC mobile phase to study the retention of alkali metal cations and ammonium ion on a sulfonic acid cation-exchange resin. The retention factors of all the ions increased with increasing concentration of 18-crown-6 in acetonitrile eluent containing 1 mM methanesulfonic acid. Most notably. 

A typical example for the significance of aliphatic amines in the pharmaceutical industry is the analysis of amylamine and tert-butylamine. Both amines are intermediates in the synthesis of a thromboxane antagonist, while tert-butyl-amine also serves as a counterion of drug components. Amylamine and tert-butylamine can be eluted with methanesulfonic acid from an lonPac CS14 cation exchanger and detected by suppressed conductivity, but different eluent concentrations are used to account for the different affinities of the two amines toward the stationary phase [462]. Moreover, amine retention can be controlled by a small amount of acetonitrile in the mobile phase. In both cases, it is fortunate that the respective drug components are soluble in water and thus can be... 

Figure 10.382 Analysis of alkali and alkaline-earth metals in a formation water on a high-capacity cation exchanger. Separator column lonPac CS16 column dimensions 250 mm x 5 mm i.d. column temperature 45°C eluent 27 mmol/L methanesulfonic acid flow rate ...

An analogous system can be used to generate methanesulfonic acid (MSA) eluent for the separation of cations (Fig. 1.10). In this case, the anode generates for eluent production. The cathode generates OH anion that combines with the H in the MSA electrolyte reservoir. MSA anion migrates across the anion exchange membrane to combine with the eluent cation (maintaining electric neutrality). 

The properties and performance of a commercial weak-acid resin column (Dionex CS12) have been described [41]. The substrate is a highly cross-linked, macroporous ethylvinylbenzene-divinylbenzene polymer with a bead diameter of 8 pm, a pore size of 6 nm, and a specific surface area of 3(X) m /g. In a second step, this substrate was grafted with another polymer containing carboxylate groups. The exchange capacity is listed as 2.8 mequiv/column for a 250 mm x 4 mm i.d. column. With this column, simple eluents such as hydrochloric or methanesulfonic acid can be used to separate mono- and divalent cations rapidly and efficiently under isocratic conditions. 

In this type of separation the analyte cations compete with the eluent cation for ion-exchange sites and move down the eolumn at different rates. The ionic eluent selected depends on the cations to be separated, the type of separation column and on the detector. In many cases an aqueous solution of a strong acid such as hydrochloric, sulfuric or methanesulfonic acid is a satisfactory eluent. Sample cations commonly separated include the following alkali metal ions (Li, Na+, K", Rb, Cs ), ammonium, magnesium, alkaline earths (Ca, Sr +, Ba ), and various organic amine and alkano-lamine cations. Most other metal cations are separated with a weakly complexing eluent. 

By using an ion exchanger with carboxyl groups or with both carboxyl and phos-phonate groups, it is possible to separate both monovalent alkali metal cations and certain divalent metal cations in a single nm. A dilute solution of a strong acid such as methanesulfonic acid is generally used as the eluent. Particular emphasis has been placed on separation of Li, Na, K, Mg + and because these ions are... 

The separation of cations is usually carried out on lonPac CS12A with sulfuric acid or methanesulfonic acid as an eluent. For anion analysis, carbonate-selective anion exchangers such as lonPac AS12A, AS14, or AS22 have proved to be suitable. Alternatively, gradient elution on lonPac ASH can be used. As a... 

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