Ion exchange SPE

A wide variety of SPE materials and cartridges are commercially available for example, alkyl-diol silica-based restrictive access materials (RAMs) and a variety of silica- and polymer-based SPE materials of different binding abilities and capacities. Reversed-phase, size-exclusion, ion-exchange SPE, and turbulence flow methods will be discussed in this chapter related to real-world applications. 

Both HPLC and GC-MS were employed for the separation, identification and quantitation of the decomposition products of indigo and indigo carmine. The chemical structures of the dyes are shown in Fig. 3.73. Carboxylic acids were preconcentrated before HPLC analysis either by ion-exchange SPE or by solid-phase microextraction. HPLC measurements were performed in a Sarasep column (300 X 7.8 mm i.d.) using 5 mM H2S04 at a flow rate of 0.7 ml/min. Analytes were detected at 215 nm. The main intermediates formed during the photocatalytic decomposition are compiled in Table 3.26. The results demonstrated that... 

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],... 

Alternatively, ionic compounds can be recovered from solution on hydrophobic sorbents using ion-pair SPE (IP-SPE). Carson [121] notes that advantages of IP-SPE over ion-suppression RP-SPE or ion-exchange SPE include selectivity, compatibility with aqueous samples and rapid evaporative concentration of eluents, and potential application to multiclass multiresidue analysis. IP reagents (e.g., 1-dodecanesulfonic acid for pairing with basic analytes or tetrabutylammonium hydrogen sulfate for pairing with... 

Method development for the LC-MS analysis of HAA in meat was performed by the gronp of Galceran [83-90]. Initially, complex mnlti-step extraction and sample pretreatment methods were applied, e.g, hqnid extraction from meat, clean-up by solid-supported LLE, and ion-exchange SPE. Later on, different SPE procednres for sample clean-np were evalnated [85]. A combination of solid-supported-LLE and SPE on C18 material was most efficient in selective elution of the polar and less polar HAA. LC was first performed on a lOOxl-mm-lD Cig column (5 pm) with 50% acetonitrile in 5 nunol/1 aqueous ammonium acetate (pH 6.7) at a flow-rate of 50 pEmin. ESl-MS was applied in SIM mode, enabling detection of HAA at 1-6 pg/kg in beef extracts [83]. 

Figure 2.12. Mechanism of ion-exchange SPE for 2,4-D. [Reproduced in modified form from Zief and Kiser (1987) and published with permission.]...

However, in order for the cation-exchange mechanism to work on atrazine, the pH of the sample must be lower than the pAT, of the analyte. This would require lowering the pH of the sample to 1.0, and a substantial amount of acid is required for this process. Furthermore, acidification to this low of a pH will protonate the organic acids naturally present in the water sample and increase the possibility of interferences when the sample is eluted from the SPE sorbent. Furthermore, the bonded-phase ion-exchange SPE cartridges are not capable of operating at this low of pH because of dissolution of the silica matrix, although it would be possible to use a polymeric sorbent. 

Metal cations may be isolated from water samples by ion-exchange SPE using... 

Figure 6.12. Example of a separation of anionic and nonionic surfactants using ion-exchange SPE.

Li, N. and Lee, Ft. K., Sample preparation based on dynamic ion-exchange SPE for GC/MS analysis of acidic herbicides in environmental waters. Anal. Chem., 72, 3077-3084, 2000. 

A clean-up procedure for the analysis of ATMA as a marker compound for ceftiofur and ceftiofur-related metabolites, based on ion exchange SPE, has been developed. Separation was carried out using reversed phase FIPLC and detection by LC-MS/MS. At the time when this chapter went to press (December 2010), this method had not yet been tested using ceftiofur incurred tissue material, and therefore this new approach has not yet been compared to current approaches. 

Ion exchange mechanism is a fundamental form of chromatography that was invented in 1935 by Adams and Holmes. The synthetic polymers or resins that contain ionizable groups are capable of exchanging ions in the solutions. The ionizable groups are either acidic or basic. The applications of ion exchange SPE include conversion of salt solutions from one form to another, desalting a solution, trace enrichment, and removal of ionic impurities or interferences. 

The sorbents used in ion exchange SPE are PS-DVB based or silica based with bonding of different ionizable functional groups such as sulfonic acid, carboxylic acid for cation exchange, or aminopropyl group for anion exchange. 

Ion exchange SPE has been frequently used as a purification method for solution-phase combinatorial chemistry. In the report for synthesis of... 

Examples of automatic purification of the library product using ion exchange SPE have been reported by Lawrence et al. As shown in reaction Scheme 10.3, the strong eation exchange cartridge (SCX from Varian) was used to extract the final products and gave pure amides (88-98% HPLC purity) in 70% to 95% yields. 

There ate several examples of the use of lEC systems for purification, isolation, and separation of heterocyclic bases. Based on ion-exchange SPE, a first and reliable procedure for the extraction of food tetrahydro-(S-carboline, is accomplished on strong cation-exchange (SCX-benzenesulfonic acid cartridges) columns. Water and/or alcoholic extracts of polyhydroxy alkaloids containing many other polar constituents are also purified by the use of resins. The acidified aqueous solution is iplied to the column and unretained neutral or acidic substances are eluted with water. The alkaloids, which... 

Company. Oligosaccharide Ig is a product of National Starch and Chemical Company. United Catalysts G-49B was provided by United Catalysts Inc. All other reagents were commercially available from multiple sources. Ion exchange SPE tubes (LC-SAX, quaternary amine, chloride counter ion) were obtained from Supelco. 

Cover the ion-exchange SPE plate with a sheet of aluminum foil. 

Repeat steps 1-3 to prepare additional ion-exchange SPE plates as necessary. 

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