Cation-exchange sorbents

Xu, W. and Regnier, EE., /. Chromatogr. A, Protein-protein interactions on weak-cation-exchange sorbent surfaces during chromatographic separations, /. Chromatogr. A, 828, 357, 1998. 

Keywords anion-exchange sorbents cation-exchange sorbents Chernobyl drinking... 

The chemical process of making cation-exchange sorbents consists of treatment PAN cloth by solutions of NH2NH2H2O and NaOH. Following chemical transformations take place after treatment by hydrazine hydrate ... 

The treatment of the cation-exchange sorbents by 1% solution of polyethylenimine at 25°C during 1 hour was selected as the optimal condition for the anion-exchange sorbents production. Capacity (Cr6+) of the sorbents is 2.0 meq/g. 

Cleanup of macrolides and lincosamides from coextracted material can also be accomplished with solid-phase extraction columns. Nonpolar sorbents such as XAD-2 resin (148) or reversed-phase sorbents (133, 134, 137, 141, 142) are usually employed in solid-phase extraction. In the latter case, ion-pairing with pentanesulfonic acid can also be applied for enhancing retention onto the hydro-phobic Ci8 material (154). However, these sorbents are not always effective for efficient cleanup of liver and kidney extracts. The basic character of macrolides and lincosamides suggests that cation-exchange sorbents such as aromatic-sulfonic acid (145,147), or polar sorbents such as silica (144,152,153), aminopropyl (139), or diol (149-151), can be powerful alternative approaches for isolation and/or cleanup of these compounds. 

Cleanup and concentration of both polar and nonpolar anticoccidial drugs from coextracted substances have mainly been accomplished with polar sorbents, such as silica (379, 391, 396, 398, 399, 402, 407, 410, 411), alumina (227, 257, 403, 404, 406, 412), or Florisil (388), since they provide high recovery of the analytes. However, in many cases, cation exchange sorbents (409), reversed-phase sorbents (405), or combinations of silica with reversed-phase sorbents (395, 400), alumina with Sephadex LH-20 (406), or alumina with Sephadex LH-20 and silica (397, 401) sorbents have been reported to be a powerful approach for the isolation and/or cleanup of these compounds. It is significant to note that cleanup systems using alumina are not suitable for isolation of lasalocid residues since they are irreversibly bound to the sorbent. 

Figure 2.28. Interactions between analytes and ion-exchange sorbents (a) strong cation-exchange sorbent and (b) strong anion-exchange sorbent.

Anion-exchange sorbents for SPE contain weakly basic functional groups such as primary or secondary amines which are charged under low-pH conditions or strongly basic quaternary ammonium groups which are charged at all pHs. Cation-exchange sorbents for SPE contain weakly acidic functional... 

Altun, Z., Abdel-Rehim, M., Blomberg, L.G. New trends in sample preparation On-line microextraction in packed syringe (MBPS) for LC and GC applications. Part III Determination and validation of local anaesthetics in human plasma samples using a cation-exchange sorbent and MEPS-LC-MS-MS. J. Chromatogr. B 813, 129-135 (2004)... 

Design a wash step that will selectively elute the interferences from the solid phase and retain the analyte. An example is the removal of urine metabolites from a cation-exchange sorbent with methanol while retaining a drug that is sorbed by cation exchange. Many metabolites in urine are organic anions and are easily removed from the sample by a methanol wash. 

For example, strong cation-exchange sorbents based on silica consist of either an aromatic sulfonic acid or a propane sulfonic acid that is bonded to the silica matrix. These sorbents typically are available in their hydrogen form and have different exchange capacities. The aromatic exchangers have approximately 1 meq/g, while the propane sulfonic acids have much less, about 0.3 meq/g. The strong cation-exchange sorbents are available in both endcapped... 

Figure 6.3. Strong cation-exchange sorbent with trifunctional bonded phase.

Elution of the ion-exchange sorbent may be carried out by several strategies. First, if the sorbent is a cation-exchange sorbent, the cations may be displaced with the of a strong acid (i.e., 20% solution of HNO3). This eluent will work well for metal cations. Another approach is to elute the cations with a more strongly held cation (Table 6.2) thus, sodium could be displaced by potassium on a... 

Strong cation-exchange sorbent. This approach would be used for organic cations and combined with a methanol eluate (50 50 methanol/water) to help prevent sorption to the matrix of the sorbent by van der Waals interactions and to assist elution. Also the pH can be adjusted in the elution solvent such that the organic cation will loose its charge that is, the pH should be two pH units above the pA. Sodium hydroxide or potassium hydroxide may be used here to raise the pH in combination with the methanol (0.1 A). Organic compounds that contain nitrogen (amines) work well by this mechanism. 

Sorbent 500 mg of strong cation exchange sorbent in form. Condition the sorbent with 3 mL methanol and 3 mL of DI water. 

Cimetidine is a drug used for the treatment of ulcers. The structure includes an imidazole ring (Fig. 6.16) that can be protonated and removed by cation exchange. The method uses a weak cation-exchange sorbent (COOH) for the isolation. 

Sorbent 500 mg of weak cation-exchange sorbent in ammonium form... 

A potential difficulty of these methods is that several elements occur as anionic species and are therefore not retained by cation exchange sorbents. Among these are Y, Zr and Mo, which form oxide interferences impeding Pd quantification (Jarvis et al. 1997). 

Also, previous to the MLC separation, chlorthalidone was extracted into diethyl ether-2-propanol from plasma, using xipamide as an internal standard [12], catecholamines were extracted from urine through alumina columns and eluted with 0.5 M perchloric acid [44] and clenbuterol in urine was eluted from a cation-exchange sorbent with the same solvent used as mobile phase (0.1 M SDS-12% 1-butanol) [45]. 

The small inner diameter of the separation capillary used in CE implies a short optical pathway, and the consequent poor concentration sensitivity when conventional UV detectiOTi is used. To overcome this drawback several techniques have been developed some of them consist in application of general approaches that are not specifically addressed to CE analysis of alkaloids. One is the use of LIF detector for analysis of alkaloids with native fluorescence [68, 69] or after their off-line derivatization [64, 88, 112]. Sample pretreatment, a second major approach, is popularly employed in combination with sample extraction and can be conveniently applied in analysis of alkaloids because they can be easily retained in cationic-exchange sorbents in solid-phase extraction (SPE) mode [113, 114]. It may be interesting to focus on more specific aspects to detect very low levels of analytes using limited amoimts of samples to this regard chemiluminescence reactions and the use of online preconcentration methods will be considered. 

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