Suppressors chemically-regenerated

Figure 3.112 Flow diagram of a micromembrane suppressor operated in the displacement chemical regeneration (OCR ) mode.

Electrochemical suppressors can also be operated without an external chemical regenerant. Hydroniimi or hydroxide ions, required for the suppressor reaction, can be generated from water by means of electrolysis. The respective reactions are given by the Eqs (3.41) and (3.42) ... 

In contrast to conventional chemical suppressors, the suppressor reaction in an SRS is directed by the electrodes. In a micromembrane suppressor, for instance, the chemical regenerant flows countercurrent through both regenerant chambers. Therefore, regenerant ions required for neutralization are provided to the eluent chamber through both membranes. Hydronium ions in an ASRS are exclusively formed at the anode, so that only the ion-exchange membrane in the anodic regenerant chamber is permeable for hydronium ions. Conversely,... 

Although capillary suppressors are electrolytically operated, the resulting background noise is not much different from that of a chemically regenerated micromembrane suppressor. 

Depending on the apphcation, a self-regenerated suppressor can also be operated in three diiferent modes, which were described in Section 3.6.4. The most common mode of operation for the CSRS 300 is AutoSuppression in the recycle mode, in which the conductivity cell effluent is used as the source for the required deionized water (see Figure 3.116 in Section 3.6.4). Because in this case an external chemical regenerant such as tetrabutylammonium hydroxide is unnecessary, cost of ownership is significantly reduced, and suppressor operation is simplified. However, this mode of operation can be used only for applications that use pure aqueous eluents. 

The basic problem of packed bed suppressors, i. e. periodic regeneration of cartridges, is not addressed by the Metrohm Suppressor Module. On the other hand, the MSM does deliver low noise, as do all chemically regenerated packed bed suppressor systems. 

In contrast to a GMMS, the suppressor reaction inside a GSRS is directed by the electrodes. In a GMMS, for instance, the chemical regenerant is directed countercurrent through both regenerant chambers. Therefore, regenerant ions... 

Recently, Talamond et al. [257] published a procedure for determining phytic acid in foods that involves anion exchange chromatography and suppressed conductivity detection and, thus, avoids post-column derivatization. Separation is carried out with an OmniPac PAX-100 using a NaOH gradient in the presence of 1 % (v/v) 2-propanol. The ASRS-1 suppressor is chemically regenerated with 25 mmol/L sulfuric acid. 

Initial attempts at introducing unnatural amino acids into proteins in mammalian cells involved the transfection of an amber suppressor tRNA that is chemically acylated with an unnatural amino acid in vitro This approach limits the amount of overall protein that can be produced since the acylated suppressor tRNA is consumed stoichiometrically and cannot be regenerated inside cells. It is also technically demanding to prepare the chemically acylated tRNA. 

In summary, a chemical suppressor containing an anionic resin (e.g. ArCH2(NR)3OH) is associated to a cationic separation column (ArS03H) in order to neutralise the mobile phase. The limitation of this type of suppressor lies in its very large dead volume that diminishes separation efficiency by remixing ions before their detection. It must be periodically regenerated and can only be used in the isocratic mode. 

In analogy to ion-exchange and ion-exclusion chromatography, the background conductance was chemically decreased in ion-pair chromatography to enable a sensitive conductivity detection. Conventional suppressor columns such as the ASC-1 (for anion determinations) and CSC-1 (for cation determinations) were initially used. After an average operation of about six hours, these columns had to be regenerated by the procedure described in Section 3.3.3. 

In 1992 Dionex introduced a commercial electrochemical suppressor called a Self Regeneration Suppressor, or SRS [6]. The internal design is similar to the membrane suppressor, but the regenerating ion for anion chromatography) is produced by electrolysis of water. This allows the use of very low flow rates for regenerant water and avoids the use of independent chemical feed needed for earlier suppression devices. 

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