Isocratic separations cations

Figure 18.1 Isocratic separation of 17 amino acids, the early appearing ones being insufficiently resolved and the last one not eluted (reproduced by permission of A. Serban, Isotope Department, Weizmann Institute of Science, Rehovot). Conditions sample, 50 ixl containing 5 nmol of each amino acid column, 15 cm x 4 mm i.d. stationary phase. Amino Pac Na-2 (cation exchanger) 7 im mobile phase, 0.4 ml min sodium citrate 0.2 N pH 3.15-sodium phosphate 1 N pH 7.4 (1 1) temperature, BB C VIS detector 520nm after derivatization with ninhydrine.

The extensive use of reversed phase ion-pair HPLC in peptides has meant that some aspects of ion-exchange HPLC are not being exploited, e.g. for peptide mapping. The isocratic separation of the two desired components from a tryptic digest of an epidermal factor fusion peptide can be achieved using a cation-exchange stationary phase in combination with a step-wise gradient of sodium chloride in... 

CS 12A Carboxylate and phosphonate High capacity, for fast isocratic separation of inorganic cations in diverse sample matrices... 

The special selectivity of lonPac CS15 with its crown ether functional groups is suitable for the isocratic separation of standard cations and monoethanol-amine, which has already been shown in Figure 4.15. Di- and triethanolamine, however, would be difficult to separate from sodium under these chromatographic conditions. If a purely aqueous methanesulfonic acid gradient is applied, the separation of all three ethanolamines can be carried out without any problem (Figure 4.81). 

Figure 10.280 Isocratic separation of pharma-ceuticaliy reievant inorganic and organic anions and cations by mixed-mode iiquid chromatography. Separator coiumn Acciaim Trinity PI, 3 pm coiumn dimensions 100mm X3 mm i.d. column temperature 30°C eiu-ent 60 40 (v/v) MeCN/20mmoi/L (totai)...

Figure 10 81 Isocratic separation of hydrox-ylamine and Af-all lhydroxylamines by cation-exchange chromatography with integrated pulsed amperometric detection. Separator column lonPac CS17 column dimensions ...

The isocratic separation between monoethanolamine and ammonium is difficult. However, potassium, ammonium, and monoethanolamine are more strongly retained when a crown ether is added to the mobile phase in this way, they can be separated from other mono- and di-valent cations. 18-crown-6 is especially suitable for this purpose. The chromatogram shown in Fig. 4-12 illustrates that under these chromatographic conditions, resolution between sodium... 

Simultaneous determination of both cations and anions in acid rain has been achieved using a portable conductimetric ion-exclusion cation-exchange chromatographic analyzer.14 This system utilized the poly(meth-ylmethacrylate)-based weak acid cation exchange resin TSK-Gel OA-PAK-A, (Tosoh , Tokyo, Japan) with an eluent of tartaric acid-methanol-water. All of the desired species, 3 anions and 5 cations, were separated in less than 30 minutes detection limits were on the order of 10 ppb. Simultaneous determination of nitrate, phosphate, and ammonium ions in wastewater has been reported utilizing isocratic IEC followed by sequential flow injection analysis.9 The ammonium cations were detected by colorimetry, while the anions were measured by conductivity. These determinations could be done with a single injection and the run time was under 9 minutes. 

For the cationic surfactants, the available HPLC detection methods involve direct UV (for cationics with chromophores, such as benzylalkyl-dimethyl ammonium salts) or for compounds that lack UV absorbance, indirect photometry in conjunction with a post-column addition of bromophenol blue or other anionic dye [49], refractive index [50,51], conductivity detection [47,52] and fluorescence combined with postcolumn addition of the ion-pair [53] were used. These modes of detection, limited to isocratic elution, are not totally satisfactory for the separation of quaternary compounds with a wide range of molecular weights. Thus, to overcome the limitation of other detection systems, the ELS detector has been introduced as a universal detector compatible with gradient elution [45]. 

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. 

Demopoulos et al. demonstrated that PL separation can be accomplished by using a cation-exchange column with an isocratic elution system of AIM/ W (300/150/35). Thus, most PLs, such... 

A step forward in simplification of multi-column systems involves the use of anion exchange and cation exchange columns connected in series. Such systems can be readily organized inside a standard isocratic ion chromatograph. In this approach a single eluent is used for separation of anions and cations and ideally the eluted analytes are detected with a single detection unit. In this way Takeuchi et al. [31 separated a mixture of Na+,... 

The reaction is followed by separation of the substrate, lactose-lysine, from the product, fructose-lysine, on a cation-exchange resin (Durrum DC6A) using an isocratic mobile phase of pyridine-acetic acid-water (6 60 176, v/v). o-Phthalaldehyde derivatives were formed and detected by fluorescence. 

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