Cation-exchange extractants

Strong cationic-exchange extraction and reversed-phase extraction (eliminates ion pairing when used in place of octadecyl silica. 

Succinate buffer extn, metal chelate affinity column cleanup, concn on cation-exchange extraction membrane... 

The method commonly proposed is based on cation-exchange extraction followed by derivatization of the fraction of interest with OPA (46,55,98,99,114,124-126) (when isolating BAs in wines). Solid-phase extraction has been performed with several stationary phases based on anionic (113) or cationic (37,39) exchangers or octadecylsilane groups (38), as well as a combination of both (51). 

Typical cation exchange extractants are di-2-ethylhexylorthophosphoric acid (HDEHP), di-n-octyl orthophosphoric acid (HDOP) and hexylphenyl phosphonic acid (HEHP). Some data on the separation factors for adjacent pairs of lanthanides are given in Table 1.22. 

D.N. Heller, S.B. Clark, H.F. Righter, Confirmation of gentamicin and neomycin in milk by weak cation-exchange extraction and ESI ion trap AIS—AIS, J. Mass Spectrom., 35 (2000) 39. 

Diketones. Beta-diketones such as acetylacetone, benzoyl-acetone, and isopropyltropolone are well known for their applications in analytical extraction of actinides. These compounds are weak acids due to tautomerization thus they can act as cation exchange extractants. Trivalent actinide [M(III)] extraction by the reagent (HA) at low aqueous acid concentration where the compound behaves both as cation exchanger and coordinator probably follows the reaction... 

An HPLC method for the more difficult measurement of plasma free metanephrines was first described in 1993. This method, like those involving measurements of plasma or urinary deconjugated metanephrines, requires a preana-lytical cation-exchange extraction and purification step. The low plasma concentrations of free metanephrines present several technical challenges. In particular, low levels of interfering substances, such as acetaminophen, tend to be more troublesome to measurements of plasma concentrations of the free metabolites than to the higher decon-... 

Cation Exchange Extractants. This class of extractants includes phenols, branched alkyl carboxylic acids, alkyl phosphoric acids, diketones, and alkyl-aryl sulfonic acids. The last group listed, sulfonic acids, are analogous to sulfonic-acid cation exchange resins and have very little selectivity. Diketones, alkyl phosphoric acids and carboxylic acids can provide both cation exchange functions and coordination functions. This feature has made bis(2-ethylhexyl)phosphoric acid one of the most versatile and powerful extractants of this type. (5) The nation below illustrates simple cation exchange extraction. 

TABLE 8,2-3 HydrometalUirgical Applications of Some Common Cation-Exchanging Extractants... 

For a cation-exchanging extractant HR, which extracts a divalent metal ion M2+ according to reaction (8.2-3), a chemical-reaction mode) of the phase equilibrium wonld be the mass-action equilibrium expression... 

Table 20 Solvation Factors Promoting Selectivity for Cs Ion in the Cation-Exchange Extraction of Alkali Metal Cations from Water to Organic Solvents...

The mother liquor of this process also contains isolysergic acid which should be recovered. This mother liquor would be the water left from the cation exchange extraction in paragraph 6. Basing this water with bicarb and solvent extraction and a KOH isomerization as in the first method should yield another measure of D-lysergic acid. 

Fbr a single cation-exchange extraction, such as reaction (8.2-3), concentratkm profiles near the in-terfece are rqitesemed by Eifi- 8.4-1. The fluxes at the interface of all four species are related by the reaction stokhiometry. The interfacial concentrations depend on the bulk-solution concentrations, die in-terfacial metal flux, and the respective mass transfer resistances. Requiring the interfaciai concentrations to be in equilibrium accordii to Eq. (8.3-1) yields the follovring equation for the metal-extraction rate ... 

Source Moore, C. M. "Solid Phase Cation Exchange Extraction of Basic Drugs from the Urine of Racing Greyhounds." Journal of the Forensic Science Society, 301990,123-129. 

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