Alumina sample cleanup

To obtain reliable chromatograms in the final step of the determination of the analytes by LC or GC, it is important to remove interfering signals resulting from coelution of other compounds. To this end, a variety of techniques are applied for cleanup of the sample extract. The most effective procedures for sample cleanup for PAH measurements are partitioning between M, N-dimethylformamide/water/cyclo-hexane and LC on silica and on Sephadex LH 20. Other cleanup procedures include LC on alumina or XAD-2 and preparative thin-layer chromatography. 

For soil samples, sufficient sample cleanup could be conducted even if the alumina column was changed to a Sep-Pak Alumina N cartridge (Waters) by the following process. The entire sample of the dried n-hexane extract (Section 6.2) is introduced into a Sep-Pak Alumina N cartridge, and the column is washed with 50 mL of n-hexane. Subsequently, pyriminobac-methyl is eluted with 3 mL of ethyl acetate, the solvent is evaporate to dryness under reduced pressure and the residue is dissolved in an appropriate volume of acetone for GC analysis. 

Packing materials for column chromatography. Adequate cleanup can be achieved with alumina instead of silica gel. Activated carbon is not suitable for sample cleanup of ripe orange and leaf. 

In alumina column cleanup, the column is first preeluted with ether-pentane mixture (30 70) before the sample extract is transferred onto the column. It is then successively eluted with ether-pentane mixture of 30 70 and 50 50% composition, respectively. This separates A-nitrosodiphenylamine. The latter elutes into the first fraction, from the interfering substance diphenylamine which goes into the second fraction along with the analytes A-nitrosodimethylaminc and A-nitrosodi-n-propy lamine. A small amount of the latter compound is also eluted into the first fraction. A cleanup procedure for other nitrosamines (not classified under U.S. EPA s priority pollutants) should generally be the same as described above. The composition of ether-pentane mixture and the elution pattern, however, must be established first before performing the cleanup. 

Ambient Air Sample collection on glass fiber filter and PUF cartridge Soxhiet extraction alumina column cleanup GC/ECD >1 ng/m 36-94 EPA 1988b (method TO-4)... 

The most widely used adsorbents for sample cleanup are silica gel, alumina, magnesium oxide (Florisil), carbon, and diatomeous soil. If large volumes of organic solvents are used, the dilution may be too great for direct determination in the chromatographic system without preconcentiation, which must be done in a way that minimizes loss of the residue components. 

Determination LC-PDA recoveries 1 to 56% preconcentration cartridges prepacked with 0.5 g of silica and 10 mg of antifluorene antibodies and OSP-2 cartridges prepacked with 80 mg of silica and 2 mg of antifluorene antibodies other preconcentration precolumns prepacked with C18 silica higher selectivity of the antifluorene immunosorbent compared to conventional cleanup (immunosorbents more reliable technique than use of alumina for cleanup of complex environmental samples) methodology using immunosorbents can be automated LOD 0.9 to 37 /ig/l... 

Plasma catecholamines The catecholamines are present in human blood plasma in the low nanomolar range, hence some preconcentration, extraction, and sample cleanup of endogenous electrophores is required prior to analysis. The catecholamines from 1 to 3 ml of plasma are adsorbed onto alumina and then eluted into 100 pi of acid to give a 10-30-fold increase in concentration. Preparation of trihydro-xyindole derivatives provides sufficient sensitivity for fluorescent detection. Reversed-phase (Cl 8) columns with addition of an anionic ion-pair reagent or specific ion-exchange columns are suitable, producing separation of all three catecholamines within 15-20 min with isocratic elution. Electrochemical detection provides acceptable specificity with an oxidation potential of -1-0.75 V when using ampero-metry. 

Alumina column cleanup makes use of highly porous granular aluminum oxide. Available in acidic, neutral, and basic pH ranges, this solid is packed into a column topped with a water-absorbing substance over which the sample is eluted with a suitable solvent, which leaves interferences on the column. After elution, the sample is concentrated, exchanged with another solvent if necessary, then analyzed. Florisil... 

For multi-analyte and/or multi-matrix methods, it is not possible to validate a method for all combinations of analyte, concentration and type of sample matrix that may be encountered in subsequent use of the method. On the other hand, the standards EN1528 andEN 12393 consist of a range of old multi-residue methods. The working principles of these methods are accepted not only in Europe, but all over the world. Most often these methods are based on extractions with acetone, acetonitrile, ethyl acetate or n-hexane. Subsequent cleanup steps are based on solvent partition steps and size exclusion or adsorption chromatography on Florisil, silica gel or alumina. Each solvent and each cleanup step has been successfully applied to hundreds of pesticides and tested in countless method validation studies. The selectivity and sensitivity of GC combined with electron capture, nitrogen-phosphorus, flame photometric or mass spectrometric detectors for a large number of pesticides are acceptable. 

The sample is homogenized with acetonitrile. An aliquot of the extract is evaporated to dryness and the residual material is dissolved in ethyl acetate-toluene (3 1, v/v), and subjected to cleanup by gel permeation chromatography (GPC). After GPC, the sample is subjected to an alumina and Florisil SPE cleanup procedure. The concentrated eluate is analysed by gas chromatography/thermionic nitrogen-specific detection (GC/TSD). 

Agonists are particularly suited to reversed-phase solid-phase extraction due, in part, to their relatively nonpolar aliphatic moiety, which can interact with the hydrophobic octadecyl- and octyl-based sorbents of the cartridge (472, 473, 475, 480,486, 487). By adjusting the pH of the sample extracts at values greater than 10, optimum retention of the analytes can be achieved. Adsorption solid-phase extraction using a neutral alumina sorbent has also been described for improved cleanup of liver homogenates (482). 

To eliminate the interference effect of other contaminants and for dirty sample extracts, cleanup may become necessary. The extract is either passed through a florisil column or an alumina column and the phthalate esters are eluted with ether-hexane mixture (20% ethyl ether in hexane, v/v). 

Various procedures described by Crippen and Smith (5) are available for identifying components in a chromatogram. Because of the limitations mentioned above, the choice of method was restricted. Peak identifications for this sample relied on cleanup and preliminary separation by column adsorption chromatography with activated alumina and Florisil, use of the chlorine- and sulfur-specific microcoulometric detector, and parallel injections onto three or more columns containing liquid substrates varying widely in polarity. 

The cleanup steps described failed to remove a trace of impurity that accompanied heptachlor, DDE, and aldrin in the alumina column chromatography. This impurity later appeared in infrared spectra obtained from small samples of these insecticides. 

Sample preparation. Sulfabromomethazine added to tissue as an internal standard, extraction with water, centrifugation, and cleanup and concentration by a series of solid phase extractions using C-18 bonded silica, acidic alumina, and AG MP-1 anion exchange microcolumns. 

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