Separation by cation exchange

Weitzhandler, M., Farnan, D., Horvath, J., Rohrer, J. S., Slingsby, R. W., Avdal-ovic, N., and Pohl, C., Protein variant separations by cation-exchange chromatography on tentacle-type polymeric stationary phases, /. Chromatogr. A, 828, 365, 1998. 

It is used in IC systems when the amperometric process confers selectivity to the determination of the analytes. The operative modes employed in the amperometric techniques for detection in flow systems include those at (1) constant potential, where the current is measured in continuous mode, (2) at pulsed potential with sampling of the current at dehned periods of time (pulsed amperometry, PAD), or (3) at pulsed potential with integration of the current at defined periods of time (integrated pulsed amperometry, IPAD). Amperometric techniques are successfully employed for the determination of carbohydrates, catecholamines, phenols, cyanide, iodide, amines, etc., even if, for optimal detection, it is often required to change the mobile-phase conditions. This is the case of the detection of biogenic amines separated by cation-exchange in acidic eluent and detected by IPAD at the Au electrode after the post-column addition of a pH modiher (NaOH) [262]. 

On allowing V(acac)3 to react with di(am)sar (172) for 3 days under N2, a deep red-brown developed.893 After separation (by cation exchange chromatography) of the red-brown product, its crystalline chloride was converted into the dithionate [Vrv(di(amH)sar-... 

The trinuclear cation Cr,(NH,) 0(OH)45 and the tetranuclear cation Crj(OH),Cr(NH have been prepared similarly by the Cr(II) charcoal catalytic method and were separated by cation-exchange chromatography (40). The trinuclear species was isolated as a bromide salt and has structure 5 in Fig. 1. The tetranuclear species Cr[(0H),Cr(NH,)4[/f has been shown to be a chromium ammonia analog of the so-called Werner s brown salt, Co[(OH)2Co(en),J 3f,f (structure 6 in Fig. 1) (41). 

Beet sugar molasses -separation by cation-exchange resin [ION EXCHANGE] (Vol 14)... 

In the work of McLaren et al. [95] butyltin species in the certified reference harbour sediment, PACS-1 were separated by cation-exchange. TBT and DBT species were speciated with a Whatman SCX column and a step gradient elution of 0.3 M ammonium acetate in 60 40 methanol water in which the pH was altered from 6 to 3 after 1 min elution. The limits of detection reported for TBT and DBT in sediment samples were 5 ngg-1 and 12 ngg, respectively. 

Reaction of four equivalents of Ni(II) with 3 resulted in a mixture of di- and trinuclear complexes, [Ni2(3)](C104)4 and [Ni3(3)(OH2)6](C104)6, which were separated by cation exchange chromatography. A tetranuclear complex, [Ni4(3)(OH2)i2](C104)8, was also obtained when the reaction mixture contained a fifty-fold excess of Ni(II). 

The hexapeptide leader sequence was removed from the fusion protein by incubation in 50 mM Tris/HCl buffer, pH 8.0, with Endoproteinase Arg-C (1 100, enzymeisubstrate, w/w), for 3 h at 37°C or overnight at 37°C (1 600, enzyme substrate, w/w). Cleavage can be monitored by analytical reverse phase HPLC, where a small decrease in retention time is observed for the cleaved product (Fig. 4). The appearance of peptides with low retention times resulting from cleavage of the MKKKWPR sequence are observed. The cleaved product is separated by cation exchange chromatography as described in Subheading... 

Originally, selective separation by cation exchange was expected to result because of large differences in the... 

Amino acid analysis. There are some 20 amino acids found in proteins and these are released by overnight hydrolysis in 6M HCl. Plasma and urine contain an even larger number of amino acids or related compounds. At low pH, amino acids are cations and for 40 years have been separated by cation exchange column, chromatography. The problem with amino adds is that in general they possess no chromophores by which they can all be detected. In the traditional amino add analyser, their detection was accomplished by a post-column reaction with nin-hydrin which forms a purple colour on heating with an amino acid at pH 5.5. This colour, Ruhemann s purple, is formed with all primary amino acids and can be detected at 570 nm. Secondary amino acids such as proline form a yellow chromophore measurable at 440 nm. 

Strelow, F. W. E., Liebenberg, C. J., Victor, A. H. Accurate determination of the major and minor elements in silicate rocks based on separation by cation-exchange-chromatography on a single column. Anal Chem. 46, 1409 (1974)... 

The bottom-up approach differs in that the entire proteome is first digested with trypsin and then the fragments are separated by cation-exchange chromatography followed by reverse phase chromatography84,124. The fragments are then analyzed by mass spectrometry and are used to identify the proteins in the sample. 

The alkali metals can be separated by cation-exchange chromatography using strongly acidic cation-exchangers [1-7]. The isolation of small amounts of lithium, and of caesium and rubidium, is described in references [8] and [9,10], respectively. The separation of Na, K, Ca, and Mg was also investigated [11]. 

Aluminium and other cations can be sorbed on cation exchangers, whereas phosphate and other interfering anions are eluted. The anionic fluoride and sulphosalicylate complexes of A1 can be separated by cation exchangers from metals that do not form the corresponding complexes. 

Two enzymatic digestions examined, separation by cation-exchange HPLC (Ionosphere-5C, Chrompack International) with gradient elution using pyridinium formate mobile phase (separation of 30 Se compounds within 60 min) ICP-DRC-MS detection ( Se, Se). 

Preparation of Enzyme. Separation and purification of the enzyme from the liver of the common squid were as follows Squid livers were mashed and dispersed in five volumes of distilled water, then acidified to pH 4.0. Much oil was eliminated. This was followed by ultrafiltration, salting out with ammonium sulfate (50% saturation), dialyzing and freeze-drying in vacuo, to yield a crude enzyme. A purified enzyme was obtained from this crude enzyme by using column chromatography. Active fractions were separated by cation exchange resin. Mono S (Pharmacia) and further purified by gel-flltration column of Superdex 75 (Pharmacia). The active fractions were collected as the purified enzyme. 

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. 

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