Column chromatographic clean-up

When samples are taken from a biologically highly productive area or in an estuary, it might be necessary to remove interfering non-hydrocarbon material by a short column chromatographic clean-up. At very low levels of petroleum pollution it has been found, however, that the clean-up procedure is more prone to contaminate the sample than to remove unwanted material. 

Basically the same procedure is applied as described in Chapter 19. Three bed volumes of 20 % dichloromethane in hexane are used to elute the sample which is reduced in volume by rotary evaporation. The concentrated solution is transferred into a volumetric flask as described above and made up to volume. This solution is ready for measurement. 

To ensure that samples were not contaminated during work-up, 25 mL n-hexane or cyclohexane rinses of the sampling bottles should be taken through the entire analytical procedure. 

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Bromacil residues in soils. The procedure uses relatively large volumes of solvents and extracts require a column chromatographic clean-up. 

Letzel, T., Rosenberg, E., Wissiack, R., Grasserbauer, M., and Niessner, R. Separation and identification of polar degradation products of benzo[a]pyrene with ozone by atmospheric pressure chemical ionization-mass spectrometry after optimized column chromatographic clean-up, J. Chromatogr. A, 855(2) 501-504, 1999. 

Water, wastewater Extracted with solvent, column chromatographic clean-up if required, concentration of extract. GC-AFID GC-TEA GC-reduction HECD NG 32% (AFID) 42% (TEA) 43% (HECD) Rhoades et al. 1980... 

Meat, vegetable Vacuun distill ground sample, extract distillate with solvent, clean up by column chromatography, derivatize with peroxytrifluoroacetic acid and column chromatographic clean up and concentrate. GC-ECD 0.2 ppb (for 250 g sample) <78% Telling 1972... 

Other comments Extract was then adjusted to 10 ml with methanol, followed by derivatization and column chromatographic clean-up, prior to GC analysis. 

Concentration of the extracts Solvent extraction under neutral conditions or at pH 11. Solvent concentrated Solvent extracted, acid washed, column chromatographic clean-up... 

Extract with DCM, filtered and concentrated Homogenized sample mixed paraffin or glycerol, water and NaOH, vacuum distilled at low temperature. Distillate extracted on-column or by shaking with solvent and concentrated Solvent extracted, column chromatographic clean-up, extract concentrated Solvent extracted by Soxhlet or sonication, extract subjected to column chromatographic clean-up, concentration of extract... 

Liquid chromatographic clean up [441,443,450] has been used either in normal phase flow using alumina, silica, or florisil [22,189,403,481,484] or with reverse-phase (RP) columns [409,452,480]. In most cases these techniques are well established and are used in an off-line mode, primarily to remove the bulk of co-extracted materials prior to a more refined clean-up prior to the final determination. These columns may be prepared in the laboratory [22,403 -405] or commercial solid phase extraction (SPE) cartridges can be used [409,452, 463,470,485,486]. In both cases, the normal phase cartridges and column materials are disposable since many of the polar co-extractants bind firmly to the substrate surface and are difficult to remove. This has been overcome to some... 

Chlorophenoxy acids are relatively polar pesticides which are usually determined by LC because volatile derivatives have to be prepared for GC analysis. This group of herbicides can be detected by multiresidue methods combined with automated procedures for sample clean-up, although selectivity and sensitivity can be enhanced by coupled-column chromatographic techniques (52). The experimental conditions for Such analyses are shown in Table 13.1. 

Ethylenethiourea (ETU) is a toxic decomposition product/metabolite of alky-lenebis(dithiocarbamates). This compound could be generated during processing of treated crops at elevated temperature. Different chromatographic methods to determine the residue levels of ETU have been published. After extraction with methanol, clean-up on a Gas-Chrom S/alumina column and derivatization (alkylation) with bro-mobutane, ETU residues can be determined by GC with a flame photometric detector in the sulfur mode. Alternatively, ETU residues can also be determined by an HPLC method with UV detection at 240 nm or by liquid chromatography/mass spectrometry (LC/MS) or liquid chromatography/tandem mass spectrometry (LC/MS/MS) (molecular ion m/z 103). ... 

Sharman, M. and Gilbert, J., Automated aflatoxin analysis of foods and animal feeds using immunoaffinity column clean-up and high-performance liquid chromatographic determination, /. Chromatogr., 543, 220, 1991. 

Miller and Hawthorne [416] have developed a chromatographic method that allows subcritical (hot/liquid) water to be used as a mobile phase for packed-column RPLC with solute detection by FID, UV or F also PHWE-LC-GC-FTD couplings are used. Before LC elution the extract is dried in a solid-phase trap to remove the water. In analogy to SFE-SFC, on-line coupled superheated water extraction-superheated water chromatography (SWE-SWC) has been proposed [417]. On-line sample extraction, clean-up and fractionation increases sensitivity, avoids contamination and minimises sources of error. 

The gas chromatographic determination of isomers of dinitrotoluene in seawater has been described by Flashimoto and co-workers [296,297]. These authors describe the complete separation of six dinitrotoluene isomers using gas chromatography with support-coated open tubular glass capillary columns and electron-capture detection. The method was applied to the qualitative and quantitative analyses of trace levels of isomers in seawater and the results were found to be satisfactory, with no need for further clean-up procedures. 

Korfmacher et al. [71] employed a short clean-up procedure followed by electron capture gas chromatography for the determination of octachlorodibenzo-p-dioxin in soils using a furzed silica capillary gas chromatographic column. The technique was suitable as a routine screening procedure for samples taken from contaminated sites. 

McIntyre et al. [58, 59] described a method for the analysis of polychlorobiphenyls and chlorinated insecticides in sewage sludges in which homogenized samples are extracted with hexane, concentrated and cleaned up on an alumina/alumina plus silver nitrate column and eluted with hexane. After concentration of the eluent, polychlorobiphenyl and organochlorine compounds were determined by a silica gel chromatographic procedure and gas chromatography. 

A gas chromatographic procedure using electron capture detection has been described for the determination of Dursban (0,0-diethyl-0 (3, 5, 6-trichloro-2-pyridyl phosphorothioate) in water and silt [95]. In this method, water samples are extracted with dichloromethane, the extract is evaporated, and a solution of the residue is cleaned up on a column of silicic acid, Dursban being eluted with hexane. The eluate is evaporated to dryness under reduced pressure, and a solution of the residue in hexane is subjected... 

The sample extract from the soil sample is dissolved in 20ml of chloroform, using an ultrasonic cleaner to facilitate solution. This and a 10ml chloroform rinse are added to a dry lOg Florisil chromatographic column and eluted with an additional 110ml of chloroform. All the eluate is collected in a Kuderna-Danish unit and evaporated just to dryness, then the first 5g Florisil column clean-up procedure is followed. 

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