Suppressor regeneration

Bond and Wallace [10] described a microprocessor-based chromatographic system which they used for the simultaneous and automated determination of Pb(II), Cd(II), Hg(II), Co(II), Ni(II), and Cu(II). Reverse-phase was used to separate in situ formed di-thiocarbamate complexes, and the system could operate continuously and unattended for periods of several days using spectrophotometric detection, and slightly less time using electrochemical detection with background suppression because this mode required frequent suppressor regeneration. 

The low-concentration eluants used to separate the sample ions on the separator column allow a substantial number of samples (typically about 50) to be analysed before the suppressor column is completely exhausted. Clearly an important practical consideration is the need to minimise the frequency of regeneration of the suppressor column and, for this reason, the specific capacity of the column is made as large as possible by using resins of moderate to high cross-linking. Some instruments contain two suppressor columns in parallel,... 

The disadvantages are that the suppressor column will increase the dispersion of the system, and it will also have to be regenerated from time to time. 

Self-regenerating suppressor cartridge incorporating an electrolysis cell, (a) For anionic analytes, (b) For cationic analytes. 

Suppressor Source Continuous Solvent compatible Capacity Regeneration mode Ion type Regenerant source... 

FIGURE 6 Effect of p-cyanophenol on the separation of perchlorate. Column 4x250mm lonPac ASII. Flow rate I.OmLmin. Injection volume 25pL. Detection suppressed conductivity utilizing the Anion Self Regenerating Suppressor (4mm), recycle mode. Ion I—perchlorate (20mgL" ). (a) Eluent lOOmM NaOH. (b) Eluent 50 mM NaOH and 5mM p-cyanophenol. 

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 order to preclude this problem and the necessary frequent regeneration of the anion system s suppressor column, an ion chromatography exclusion scheme was utilized. Samples collected in a mine environment were reliably concentrated by freeze-drying and then analyzed on an ICE system with dilute hydrochloric acid eluent. The precision of the ICE method was experimentally determined to be 2.5% in a concentration range of 1 to 10 yg/mL. The accuracy was not independently determined but good precision and recovery yield confidence that measured values are within 5% of the true value. No interferences were observed in the ICE system due to strong acids, carbonic acid or other water soluble species present in mine air subject to diesel emissions. 

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. 

Figure 4.8—Membrane and electrochemically regenerated suppressors. Two types of membrane exist those that allow the permeation of cations (H+ and Na+) and those that allow the permeation of anions (OH and X ). a) The microporous cationic membrane model is adapted to the elution of an anion. Only cations can migrate through the membrane (corresponding to a polyanionic wall that repulses the anion in the solution) b) Anionic membrane suppressor placed after a cationic column and in which ions are regenerated by the electrolysis of water. Note in both cases the counter-current movement between the eluted phase and the solution of the suppressor c) Separation of cations illustrating situation b).

Fig. 24 Schematic of the self-regenerating suppressor in a recycle mode. (Courtesy of Dionex.)...

Fig. 5. An analysis of a coarse atmospheric aerosol extract by CE and IC [49]. CE conditions a 57 cmX75 xm I.D. capillary, distance to detector, 50 cm. Electrolyte 2.25 mM PMA (pyromel-litic acid), 0.75 mM HMOH (hexamethonium hydroxide), 6.50 mM NaOH and 1.60 mM TEA (triethanolamine), pH 7.7 or 2.0 mM NDC (2,6-naphthalenedicarboxylic acid), 0.5 mM TTAB (tetradecyltrimethylammonium bromide) and 5.0 mM NaOH, pH 10.9 30 kV (PMA) or 20 kV (NDC) pressure injection for 10 s indirect UV detection at 254 nm (PMA) or 280 nm (NDC). IC conditions an IonPac-ASlO column with an IonPac-AGlO guard precolumn conductivity detection using an anion self-regenerating suppressor (ASRS-I) in the recycle mode. Analytes 2, chloride 3, sulfate 5, nitrate 6, oxalate 7, formate 10, hydrocarbonate or carbonate 11, acetate 12, propionate 14, benzoate.

In Fig. 2, the columns were IonPac ICE-AS6 (250X9-mm i.d.), AG9-HC (concentrator, 50X4-mm i.d.) and AG9-HC/AS9-HC (analytical, 250X2-mm i.d.). The ion exclusion sample treatment eluent was deionized water and the flow rate was 0.55 ml/min. The sample volume was 750 pi. The ion exchange eluent was 8.0 mM sodium carbonate and 1.5 mAf sodium hydroxide. The flow rate on the 2-mm analytical column was 0.25 ml/ min. Detection was by suppressed conductivity using the ASRS -I electrolytically regenerated suppressor in the external water mode. 

---