Cation exchange isocratic separation

The most accurate measurements of creatinine involve some form of separation, so an on-line method is very useful. Figure 10.2 shows a simple cation exchange isocratic HPLC assay that can be easily set up in a metabolic laboratory. The urine is simply diluted prior to injection. Creatinine is detected by its UV absorption but the figure clearly shows that trace amounts of other compounds must be resolved if a precise assay is to be achieved. 

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. 

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. 

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.

Fifth method a subsample of 150 mg was ultrasonically extracted with a mixture of methanol/methane (5/2 v/v) (4 x 2.8 mL) and back-extracted in water the extract was evaporated under N2 stream and stored in a glass flask at 4°C in the dark. Separation was by cation exchange LC (Chrompack Ionosphere) in isocratic mode (pyridinium formate). Final detection was by ICP-MS of mass 75. 

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... 

Lysozyme and ribonuclease were separated by cation-exchange gradient elution (both strong and weak ion dtange columns) as a function of gra dient time and flow rate (2S). Values of Z were obtained from isocratic data (Fig. 8) and used to predict Ox values for these gradient runs. There data are summarized in Table XI. Overall agreement is acceptable, with 0.98 and SD 0.17 for 14 ta points. 

A quality feature of all cation exchangers suitable for simultaneous analysis of mono- and divalent cations is the maximal concentration ratio between sodium and ammonium that allows a separation of both components. Under isocratic conditions with lOmmol/L methanesulfonic acid at 2mL/min, lonPac CS12... 

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