Capture chromatography

In addition to clarification, the extract usually has to be conditioned to match the requirements for the subsequent capture chromatography step, e. g. by reduction of conductivity or adjustment of pH. These manipulations may lead to either immediate or delayed precipitation of extract components, which have to be removed before further processing. Careful design and evaluation of the extraction procedure is therefore an important development task for every individual process. 

Deubert [1] has discussed the sources of compounds which interfere in the analyses in water and soil extract for DDT and Dieldrin by gas electron capture chromatography. Nitration of these insecticides eliminated their peaks so that background interference peaks could be studied. 

A significant feature of plasmid purification employing capture chromatography (i.e. involves plasmids binding to the chromatographic beads) is the low plasmid-binding capacities observed. 

If an ion exchange step will be used as an initial capture chromatography step, pH or conductivity adjustment of the conditioned medium might be nece-sary. At large scale, conductivity adjustment can be accomplished by in-line dilu-... 

Weiss, R. F. (1981). Determination of carbon dioxide and methane by dual catalyst flame ionization chromatography and nitrous oxide by electron capture chromatography. J. Chromatogr. Sci. 19, 611-616. 

Method 508, Determination of Chlorinated Pesticides in Water by Gas Chromatography with an Electron Capture Chromatography, Rev. 3.1, USEPA, Cincinnati, OH, 1995. 

The chromatogram can finally be used as the series of bands or zones of components or the components can be eluted successively and then detected by various means (e.g. thermal conductivity, flame ionization, electron capture detectors, or the bands can be examined chemically). If the detection is non-destructive, preparative scale chromatography can separate measurable and useful quantities of components. The final detection stage can be coupled to a mass spectrometer (GCMS) and to a computer for final identification. 

Schematic diagram of an electron capture detector for gas chromatography.

Environmental Analysis One of the most important environmental applications of gas chromatography is for the analysis of numerous organic pollutants in air, water, and wastewater. The analysis of volatile organics in drinking water, for example, is accomplished by a purge and trap, followed by their separation on a capillary column with a nonpolar stationary phase. A flame ionization, electron capture, or... 

Selectivity Because it combines separation with analysis, gas chromatography provides excellent selectivity. By adjusting conditions it is usually possible to design a separation such that the analytes elute by themselves. Additional selectivity can be provided by using a detector, such as the electron capture detector, that does not respond to all compounds. 

Pesticides. Chlorinated hydrocarbon pesticides (qv) are often found in feed or water consumed by cows (19,20) subsequently, they may appear in the milk, where they are not permitted. Tests for pesticides are seldom carried out in the dairy plant, but are most often done in regulatory or private specialized laboratories. Examining milk for insecticide residues involves extraction of fat, because the insecticide is contained in the fat, partitioning with acetonitrile, cleanup (FlorisH [26686-77-1] column) and concentration, saponification if necessary, and determination by means of paper, thin-layer, microcoulometric gas, or electron capture gas chromatography (see Trace and residue analysis). 

Gas Chromatography. Gas chromatography is a technique utili2ed for separating volatile substances (or those that can be made volatile) between two phases, one of which is a gas. Purge-and-trap methods are frequently used for trace analysis. Various detectors have been employed in trace analysis, the most commonly used being flame ioni2ation and electron capture detectors. 

Trihalomethanes. Wherever chlorine is used as a disinfectant in drinking-water treatment, trihalomethanes (THMs) generaUy are present in the finished water. The THMs usuaUy formed are trichloromethane (chloroform), bromodichloromethane, dibromochloromethane, and tribromomethane (bromoform). There are four main techniques for the analysis of THMs headspace, Hquid— Hquid extraction (Ue), adsorption—elution (purge—trap), and direct aqueous injection. The final step in each technique involves separation by gas—Hquid chromatography with a 2 mm ID coUed glass column containing 10 wt % squalene on chromosorb-W-AW (149—177 p.m (80—100 mesh)) with detection generaUy by electron capture. 

Ca.rhora.nes, These are used in neutron capture therapy (254), and as bum rate modifiers in gun and rocket propellants. They are used as high temperature elastomers and other unique materials, high temperature gas—Hquid chromatography stationary phases, optical switching devises (256), and gasoline additives (257). 

Ethylene dibromide Lab method with pumped Tenax absorbent tubes, solvent desorption and electron capture gas chromatography 45... 

Figure 13.2 MDGC-ECD chromatograms of PCB fractions from sediment samples, demonstrating the separation of the enantiomers of (a) PCB 95, (b) PCB 132, and (c) PCB 149 non-labelled peaks were not identified. Reprinted from Journal of Chromatography, A 723, A. Glausch et al, Enantioselective analysis of chiral polyclilorinated biphenyls in sediment samples by multidimensional gas cliromatography-electi on-capture detection after steam distillation-solvent exti action and sulfur removal , pp. 399-404, copyright 1996, with permission from Elsevier Science.

J. C. Duinker, D. E. Schult and G. Petiick, Multidimensional gas chromatography with electi on capture detection for the deteimination of toxic congeners in polycWorinated biphenyl mixture . Anal. Chem. 60 478-482 (1998). 

Y. V. Gankin, A. E. Gorshteyn and A. Robbat-Jr, Identification of PCB congeners by gas chromatography electi on capture detection employing a quantitative sti ucture-retention model , Aim/. Chem. 67 2548-2555 (1995). 

---