Ion exchange sorbents

The coordination chemistry of the trichalcogenophosphonates is very undeveloped when compared to the analogous metal organophosphonates (RP032), which have been extensively studied owing to their potential and practical applications as ion exchangers, sorbents, sensors, proton conductors, nonlinear optical materials, photochemically active materials, catalysts and hosts for the intercalation of a broad spectrum of guests.145... 

Polyacrylonitrile (PAN) cloth with surface density of 1.0 kg/m2 and thickness of 10 mm was utilized as the raw material for making ion-exchange sorbents. 

Although Certify is a mixed mode sorbent with C8 and sulfonic acid moieties, the authors rationalized that the hydrophobic retention on this sorbent is more dominant and caused the nonretention of certain drugs during methanol wash. The weak WCX ion exchanger was also excluded for similar reasons. Both the mixed mode strata-X-C and the ion exchange sorbent SCX were found to be most amenable for the derivatization-based GC/MS analysis and both yielded pure extracts. However, the yields were consistently lower with strata-XC than SCX and the authors hypothesized that this was due to the inability of the 5% ammonia/methanol eluent to completely disrupt the hydrophobic and dipolar interactions between the analytes and XC. 

Method development in SPE begins with an analysis of the sample matrix as well as the sample analytes. One of the most efficient mechanisms of SPE is to use mixed-mode ion exchange sorbents. If the analytes are bases, cation exchange is the most selective SPE mode. If the analytes are acids, anion exhange is the most efficient. However, it is sometimes easier to capture the matrix components and allow the analytes to pass through the sorbent unretained. 

Ion-exchange sorbents allow extraction of ionic hydrophilic analytes that are difficult or impossible to isolate with liquid-liquid extraction. The applied sorbents are permeable hydrophilic polymers or hydrophilic polymers bound to silica containing a fixed concentration of acidic and/or basic functions on the surface. In the anion exchange mode, the sorbent surface is covered with posi-... 

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

Each of the types of SPE sorbents discussed retains analytes through a primary mechanism, such as by van der Waals interactions, polar dipole-dipole forces, hydrogen bonding, or electrostatic forces. However, sorbents often exhibit retention by a secondary mechanism as well. Bonded silica ion-exchange sorbents primarily exhibit electrostatic interactions, but the analyte also experiences nonpolar interaction with the bonded ligand. Nonpolar bonded silicas primarily retain analytes by hydrophobic interactions but exhibit a dual-retention mechanism, due to the silica backbone and the presence of unreacted surface silanol groups [72], Recognition that a dual-... 

Ionic water-soluble compounds can be retained by ion-exchange sorbents or by reversed-phase (RP) sorbents if ionization is controlled by ion suppression (i.e., by pH control that produces the nonionized form). In ion-exchange SPE, retention occurs at a sample pH at which the analyte is in its ionic form, whereas the analyte is desorbed in its neutral form if the analytes are ionic over the entire pH range, desorption occurs by using a solution of appropriate ionic strength [92],... 

Adsorption of analytes on ion-exchange sorbents is based on electrostatic interactions between charged functional group in the compounds of interest and the positively or negatively charged groups on the stationary phase (bonded to the silica surface). 

Reduction in expenditure for ion exchangers, sorbents, and auxiliary chemical reagents. 

A. I. Vulikh et al.. Technical and Economical Requisites for Application of Ion-Exchange Sorbents in Purification of Gases, Ion Exchange and Chromatography, Voronezh, 1976, p. 260, GOST 10899-75. 

G. I. Nikandrov, Purification of Gases from Sulphur Anhydride by Ion-exchange Sorbents. Industrial and Sanitary Purification of Gases, 4(1975) 14. 

However, the R group can contain any of the functional groups shown in Table 1.1. This includes reversed phases, such as C-2, C-4, C-8, C-18, cyclohexyl, phenyl, and even a single C-1 is available. The cyclohexyl and phenyl groups typically are bonded with a three-carbon alkyl chain connecting them to the surface of the silica gel. Likewise, the normal-phase sorbent and ion-exchange sorbents typically will contain a three-carbon linking chain to the silica-gel surface. Structures are shown in later chapters on reversed-phase and normal-phase SPE. 

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