Selection elution

Cytochalasin B (from dehydrated mould matter) [14930-96-2] M 479.6. Purified by MeOH extraction, reverse phase Cl8 silica gel batch extraction, selective elution with 1 1 v/v hexane/tetrahydrofuran, crystn, subjected to TLC and recrystallised [Lipski et al. Aruil Biochem 161 332 1987]. 

Lord and Pawliszyn" developed a related technique called in-tube SPME in which analytes partition into a polymer coated on the inside of a fused-silica capillary. In automated SPME/HPLC the sample is injected directly into the SPME tube and the analyte is selectively eluted with either the mobile phase or a desorption solution of choice. A mixture of six phenylurea pesticides and eight carbamate pesticides was analyzed using this technique. Lee etal. utilized a novel technique of diazomethane gas-phase methylation post-SPE for the determination of acidic herbicides in water, and Nilsson et al. used SPME post-derivatization to extract benzyl ester herbicides. The successful analysis of volatile analytes indicates a potential for the analysis of fumigant pesticides such as formaldehyde, methyl bromide and phosphine. 

Elution. The compound of interest is selectively eluted with a stronger solvent. 

Klink [135] recently discussed sample preparation procedures for LC-MS. SPE can be so well integrated into the concept of LC-MS, that in many automated applications no clear distinction exists between SPE and LC [135]. In on-line LC-MS mode, the possibilities for changing the eluent are rather limited, because of the tolerance of the eluent for the interface. Moreover, the conventional gradient mode may lead to strong fluctuations in the response of the MS detector. Here the off-line mode, using SPE for concentration followed by selective elution, enables very far-reaching preseparation, due to the differences in the polarity of the eluents applied and their mixtures. Although the overall benefits of SPE for LC-MS applications are positive, extracts... 

Selective Elution of Flavonoids from Terpenoids in Ginkgo biloba Leaf Extracts... 

Selectively elute compounds with 1 mt of solvent or less... 

In environmental analytical applications where analyte concentrations, e.g. surfactants or their metabolites, are quite low, extraction and concentration steps become essential. Solid phase extraction (SPE) with cartridges, disks or SPME fibres (solid phase micro extraction) because of its good variety of SP materials available has become the method of choice for the analysis of surfactants in water samples in combination with FIA as well as LC—MS analysis. SPE followed by sequential selective elution provides far-reaching pre-separations if eluents with different polarities and their mixtures are applied. The compounds under these conditions are separated in the MS spectrometer by their m/z ratios providing an overview of the ionisable compounds contained in a sample. Identification in the sense it has been mentioned before, however, requires the generation of fragments. 

Here, the mixture analytical FIA-MS-MS approach reached its limitation to identify compounds. Hence, LC separations prior to MS analysis are essential to separate compounds with the same m/z ratio but with different structures. The behaviour in the LC separation will be influenced by characteristic parameters of the surfactant such as linear or strongly branched alkyl chain, the type, the number and the mixture of glycolether groups—PEG and/or PPG—and the ethoxylate chains. The retardation on SPE materials applied for extraction and/or concentration also depends on these properties and can therefore be used for an appropriate pre-separation of non-ionic surfactants in complex environmental samples as well as in industrial blends and household detergent formulations. A sequential selective elution from SPE cartridges using solvents or their mixtures can improve this preseparation and saves time in the later LC separation [22],... 

In a screening approach, non-ionic surfactants were monitored in the form of their [M + NH4]+ ions, equally spaced with Am/z 44 and identified by FIA-MS-MS(+) in combination with APCI or ESI interface [34,35]. Ci8-SPE was performed prior to selective elution by diethyl ether [35]. Ions of the non-ionics of AE type at m/z 350-570 (Am/z 44) were identified as surfactants with the general formula Ci3H27-0(CH2CH20)mH (m = 3-7). The complexity of the mixture confirmed the results using the diagnostic parent scans m/z 89 for aliphatic non-ionic surfactants of ethoxylate type necessary [35]. 

Surface water samples often contain surfactants and their metabolites. After Cis-SPE combined with selective elution [7,9,10] the metabolites, PEG and PPG, were observed in the ether fraction (PPG) or in the combined methanol-water and methanol (PEG) fractions, respectively. They could be ionised in the form of their [M + NH4]+ ions applying ESI-FIA-MS(-I-) in combination with ammonium acetate for ionisation support. ESI-LC-MS(-I-) resulted in an excellent separation of both metabolites, as presented in the total ion current (TIC) trace in Fig. 2.9.6(7) together with selected mass traces of PEG (m/z 300, 344 and 388) and PPG (m/z 442, 500, 558) (Am/z 44 and 58) in Fig. 2.9.6(l)-(6) [36],... 

Fig. 2.9.6. (Inset) ESI-FIA-MS(+) overview spectrum of (a) PEG homologues and (b) PPG homologues contained in wastewater effluent SPE extract (7) ESI-LC-MS(+) RIC and selected mass traces of (l)-(3) PEG and (4)-(6) PPG homologues from mixture of (a) and (b) CiS-SPE with selective elution, compounds ionised as [M + NH4]+...

For the identification of surfactants in influent and effluent samples from German and Greek wastewater treatment plants, Schroder and co-workers [4,5] employed an analytical approach comprising SPE, selective elution and screening analysis by flow-injection analysis (FIA)-MS(MS) in combination with liquid chromatography-(tandem)... 

The mixed lanthanide (III) ions (Ln3+) can be absorbed from solution at the top of a column of a cation-exchange resin RSOsNa (Section 14.4) and then selectively eluted from it, that is, swept down the column in bands by a stream of a solution of a substance that competes with the Ln3+ for sites in the resin. An acidic tribasic chelating agent H3X (usually citric acid/sodium citrate buffer) is used so that, as in reaction 17.16, the tendency for a specific Ln3+ to form neutral LnX and so escape the electrostatic... 

This paper describes a new reaction which may yield useful amounts of the product isotope following neutron capture by lanthanide or actinide elements. The trivalent target ion is exchanged into Linde X or Y zeolite, fixed in the structure by appropriate heat treatment, and irradiated in a nuclear realtor. The (n, y) product isotope, one mass unit heavier than the target, is ejected from its exchange site location by y recoil. It may then be selectively eluted from the zeolite. The reaction has been demonstrated with several rare earths, and with americium and curium. Products typically contain about 50% of the neutron capture isotope, accompanied by about 1% of the target isotope. The effect of experimental variables on enrichment is discussed. 

If gentle and selective elution methods do not release the bound macromolecule, then mild denaturing agents can be added to the buffer. These... 

After leaching, a concentration/pmification is done to get rid of other materials leached from the ore. This can be done by ion exchange or solvent extraction. In the ion exchange method, three steps are employed (a) the absorption of uranium from the leach liquor onto the resin, (b) the selective elution of uranium from the resin, and (c) the regeneration of the resin. Anion exchange is the preferred method of ion exchange with the relevant chemical reactions for acid leach being... 

The purification of glutamine cyclotransferase from papaya latex has been carried out by Messer and Ottesen (116). A batch procedure was used for the removal of impurities by passage of a papaya latex extract through a thin layer of carboxymethyl-Sephadex the active protein was separated by selective elution. Additional purification was achieved by chromatography on a column of carboxymethyl-Sephadex and by gel filtration on Sephadex G-100. The purified enzyme was homogeneous by the criteria of paper electrophoresis, ultracentrifugation, and gel filtration on Sephadex G-100 columns and chromatography on carboxy-methyl- or DEAE-Sephadex. The electrophoretic behavior of the enzyme indicates that it is a basic protein with an isoelectric point near... 

According to Patel et al. (140), Amberlite XAD-2 can also be used to separate water-soluble food colors. Food colors were retained only with neutral eluent (methanol). By changing the concentration of methanolic sulfuric acid, selective elution of colors is achieved. 

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