Cation columns

FIGURE 10 Isocratic CEC of erythromycin A and its impurities. Cationic column 30cm (effective length 20 cm) x 50 pm ID mobile phase 25% (v/v) acetonitrile and 25% (v/v) ethanol in 30mM phosphate buffer, pH 8.0 applied voltage — l5kV detection, 206 nm. Sample (I) N-demethylerythromycin A, (2) erythromycin C, (3) erythromycin A, (4) erythromycin B, (5) erythromycin enol ether. Mobility of EOF measured with DMSO, peof = 3-33 x 10 °m /sV. (Reprinted from reference 321, with permission.)... 

In the two NaX, L3 structures, triads of oxygen atoms are shared between pairs of cations, giving rise to infinite cationic columns. In NaBr, (CH3CONH2)2 6-coordination is achieved by sharing of one bromide ion (Na—Br = 3.05 A) and two oxygen atoms (Na—O = 2.35 A) between pairs of sodium ions to give electrically neutral columns which are held in the other two dimensions by N—H. . . Br bonding (23). 

In the case of peptide separation by HPLC, separation modes are combined in series. This approach is called tandem LC. For instance, ion exchange associated with RP is used for peptide separation. Multidimensional protein identification technique (MudPIT) involving use of microcapillary columns (SCX cationic column and RP column) linked in series and eluted into MS is preferred for separation of complex peptide mixtures (Figure 5.4). 

Dissolution Cation Column Evaporation Anion Column Evaporation... 

Separation of cations Column IC-Pak (Soc. Waters) 150x3.9 mm Conductivity detection Elution 0.1 M EDTA/3 mM N03H Flow t mL/min... 

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. 3. IEC/CEC separation of anions and cations. Column TSK-Gel OA-Pak A (300 X 7.8 mm, 5 jam) eluent 5 mM malic acid-methanol (95 5) flow rate 1.2 ml/min sample volume 25 jal detection conductivity. Peaks (1) sulfate, (2) chloride, (3) nitrate, (4) fluoride, (5) sodium, (6) ammonium, (7) potassium, (8) magnesium, (9) calcium. Reprinted with permission from [19].

Because Mn2+ is a polyvalent cation, its concentration in the final solution feed to the cation columns should be kept below 0.05M to avoid excess competition for resin sites. For the overall process, it is better to use the longer oxidation times than to use higher Mn2+ concentration. Catalyzed oxidation should not be performed until the volume of solution is reduced to the minimum possible volume. 

The Au foil Is quickly dissolved In aqua regia and the Au extracted with ethyl acetate for 1 min. The aqueous phase is then eluted through a Dowex-1 anion resin column (2 zmn diameter, 1 cm long) with 6 M HC1 to complete the removal of Au end other impurities. The dropB. containing the actinide fraction are evaporated and the activity is then eluted through a Dowex-50 resin cation column with 0.4 M soln. of ammonium Q -hydroxy-isobutyrate, which is adjusted to pH 4.0 with HH4OH to separate the various actinide elements from each other, (Mv-Fm-E-Cf)... 

Cation Column Effluent Quality As the water passes down the column stoichiometric ion exchange occurs to give a dilute mixture of acids as given by the following reactions ... 

The cation exchange step is exactly as described for the Strong Acid Cation (SAC)-Strong Base Anion (SBA) process but now the acidic cation column effluent passes down a column of weakly basic anion exchange resin. The strong mineral acids are taken up by the anion resin through addition to form the acid salt forms, whilst the too weakly acidic dissolved carbon dioxide and silica pass through unaffected (Chapter 4). 

Section 3.4.4). The dimensions of the Fast-Sep-Cation column are 250 mm x 4 mm I.D. Compared to the CS3 column, the 13-pm particle diameter of the substrate is slightly higher. The sulfonated latex beads are crosslinked with 4% DVB and have a diameter of about 225 nm. 

The selectivity of low capacity cation columns for monovalent ions can be adjusted by the addition of an organic modifier to the eluent. Using a nitric acid eluent of pH... 

Figure 4.3 Separation of several cations, mono and divalents with a cationic column (Courtesy of AUtech)...

Suppose that a mixture containing the cations Na and K+ has been separated using a cationic column whose mobile phase contains dilute hydrochloric acid. In this acidic medium, at the outlet of the column, the Na and the K+ ions... 

Figure 4.9 Chemical suppressor for an exchange cation column. For cation analysis, the mobUe phase is often dilutes HCl or HNO3 solutions, which can be neutralized by an eluent suppressor that supplies OH . In this example the anionic suppressor purges the mobile phase of H+ ions and of almost aU of the Cl ions, facilitating the detection of the cation M. The same principle holds for anion analysis. In this case, the mobile phase is often dilute NaOH or NaHC03, and the eluent suppressor supplies H+ to neutralize the anion and retain or remove the Na+.

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