Zone-interference chromatograph

Figure 6. Schematic presentation of a zone-interference chromatographic experiment with a fast-moving macromolecule (M) and two small ligands LI and L2 of equal molecular dimensions but different complexing abilities to M (LI L2). A, conditions in the column in the beginning (to) and after time tj< B, elution profile corresponding the situation at time t. ...

Note When combined with thin-layer chromatographic separation the reagent provides a specific detection method for nitrate and nitrite. The color development is often completed within a few minutes on silica gel plates. In the absence of ammonia vapor traces of oxides of nitrogen in the laboratory atmosphere can slowly cause the background to become reddish-brown. The simultaneous presence of the following ions in the chromatogram zones interferes with the detection of nitrate/nitrite I , 10J, IO4, MoO and H2PO2. 

TLC can be applied to the preliminary isolation of the compound under analysis from complex mixtures or to the purification of the products after a derivatization reaction. Several examples of TLC conditions for various substances and/or derivatives are given in Table 2.1. In all instances TLC must be carried out in such a way that it will contribute to the solution of a given analytical problem and that it should not become a source of difficulties and errors. As in the preceding instance, contamination of the sample with incidental impurities from the solvents used should be prevented. Chromatographic materials should also be tested for the presence of substances that could interfere with the compounds under analysis in the chromatogram. The quantitative recovery of individual zones from the layer for further treatment is obviously a prerequisite for reliable results. 

Prepare a sample solution in which the analyte is completely dissolved and impurities have been reduced to a level at which they will not produce chromatographic zones that interfere with scanning of the analyte. 

The zone elution quantification method is tedious and time consuming and is likely to be inaccurate because of difficulties in locating the exact zone boundaries, loss of sorbent during scraping and collection, nonreproducible or incomplete elution from the sorbent, and background interferences due to eluted impurities from the sorbent. These errors are minimized if standards and samples are chromatographed, scraped, and eluted together as consistently as possible, and if an equal-size blank... 

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