Suppressor hollow fiber membrane

Suppressor devices include packed column suppressors, hollow-fiber membrane suppressors, micromembrane suppressors, suspension postcolumn reaction suppressors, autoregenerated electrochemical suppressors, and so forth. 

Some of the drawbacks that packed column suppressors have were eliminated when hollow-fiber membrane suppressors were introduced in 1981. These were found to be even more convenient and efficient, with low dead volume and high capacity, and they are dynamically regenerated. Eluent passes through the... 

Eluents and regenerents suitable for the analysis of organic acids when applying an AFS-2 hollow fiber membrane suppressor are listed in Table 4-2. For the analysis of borate and carbonate with octanesulfonic acid as the eluent, an ammonium hydroxide solution with a concentration c = 0.01 mol/L can also be used as the regenerent. 

Eluents and regenerants suitable for the analysis of organic acids when applying an AFS-2 hollow fiber membrane suppressor are listed in Table 5.2. For the... 

Figure 9.12. Alternative forms of suppressor column for ion chromatography (a) hollow fiber, (b) membrane sandwich. Reprinted by permission of Dionex Corporation, Sunnyvale, CA.

In contrast to conventional suppressor columns, hollow fiber suppressors are continuously regenerated, and thus do not require an additional pump system. The reactions that occur across the membrane wall are shown in Fig. 3-37. Since fiber suppressors suited for anion exchange chromatography act as cation exchangers, the eluent cations are exchanged with protons in the regenerent solution. The driving force for the diffusion of protons across the membrane is provided by their subsequent reaction with... 

The CFS hollow fiber suppressor (see Section 3.4.3) that was developed for cation exchange chromatography can also be applied to cation analysis via ion-pair chromatography. It features good solvent stability and sufficient membrane transport properties for the anionic ion-pair reagent. This suppressor is regenerated with tetramethylam-monium hydroxide using a concentration of c = 0.04 mol/L. 

As described in Sections 3.3.3 and 3.4.3, hollow fiber suppressors no longer represent the state-of-the-art. Thus, a micromembrane suppressor was introduced under the trade name AMMS-MPIC for ion-pair chromatography of anions. Its structure corresponds to the systems developed for ion-exchange and ion-exclusion chromatography. Like the AFS-2, the AMMS-MPIC micromembrane suppressor contains a solvent-resistant membrane that is permeable to quaternary ammonium bases. Regarding the exchange... 

This benchmark publication was followed by a series of developments that continues to this day in the evolution of IC as a trace determinative technique. The Dionex Corporation was formed out of these developments from Dow Chemical in the mid-1970s and this company has been quite an innovator in the manufacture of instrumentation for suppressed IC. From the earlier model such as the 10 to the 20001 to the DX 500 from the cation-exchange column to the hollow-fiber cation suppressor to the micro-membrane cation suppressor to the self-regenerate cation suppression for anion analysis and now to their just add water slogan, Dionex Corporation has made considerable advances in IC technology. A nonsuppressed form of IC also developed during the 1970s. To quote from the author s abstract of this benchmark paper (97) ... 

The fiber suppressor [3, 4] was the first device based on the use of an ion-exchange membrane. It consisted of a long, hoUow fiber made of a semi-permeable ion-exchange material. Column effluent containing zones of separated sample ions passed through the hoUow center of the fiber. Here the sodium counterion was exchanged for from the membrane. The outside of the hollow fiber... 

The comparatively higher suppression capacity of a micromembrane suppressor is not caused only by the higher diffusion efficiency of eluent cations to the membrane wall. The screen s ion-exchange characteristics have an even greater impact they are directly proportional to the suppression capacity. In continuously regenerated suppressors, one talks about the dynamic cation-exchange capacity. Therefore, the suppression capacity is defined for both the hollow fiber suppressor and the micromembrane suppressor according to Eq. (3.38) as the product of eluent concentration and eluent flow rate ... 

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