Detection of zones

The solvent in which the detection reagent is dissolved can affect results significantly. For example, acetone appears to be the best solvent, in terms of rate of color formation, intensity and exact color produced, for ninhydrin reagent. Pyridine acts as a ninhydrin color stabilizer and so is often included when detecting amino acids. In general, acetone is a superior solvent for many PC detection chemicals with which it is compatible. 

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The measurement of the relative mobilities of substances, using the gradient detection of zones and the comparison of the data obtained with tabulated values, may serve as a useful and simple procedure for the qualitative orientation. The qualitative index... 

Thermal derivatization (or thermochemical reaction) allows detection of zones without the use of reagents. For example, simple heating of amino-modified silica layers causes conversion of sugars, oligosaccharides, creatine, catecholamines, steroid hormones, and other compound types to stable fluorescent compounds. Heating times of 3—45 min and temperatures of 140-200°C have been used for different substances. 

Detailed comparisons of TLC to other chromatographic methods, especially HPLC, and TLC to HPTLC are presented in Chapter 1 of Ref. 1. TLC involves the concurrent processing of multiple samples and standards on an open layer developed by a mobile phase. Development is performed, usually without pressure, in a variety of modes, including simple one-dimensional, multiple, circular, and multidimensional. The detection of zones is done statically with an assortment of diverse possibilities. Paper chromatography, which was invented by Consden, Gordon, and Martin in 1944, is fundamentally very similar to TLC, differing mainly in the nature of the stationary phase. Paper chromatography has lost favor compared to TLC because the latter is faster, more efficient, and allows more versatility in the choice of stationary and mobile phases. 

Color. Deep red color of naphthalene-j8-sulfonic acid salt facilitated detection of zones. Identical separations achieved by either ascending or circular chromatography... 

When the amonnt of material to be chromatographed is small (<200 mg), preparative TLC is an option worth trying, if detection of zones is feasible. The plate can be developed multiple times, if necessary, and it often gives better resnlts than a small column. 

Substances giving ultraviolet absorption, or fluorescence, or marked with radioisotopes could, with small changes in experimental arrangements, be followed in the actual experiment. As far as the authors are aware, such techniques have not yet been utilized although they would possess some definite advantages. The properties referred to have been used for the detection of zones in finished experiments. 

Lappala, E. and G. Thompson. Detection of Groundwater Contamination by Shallow Soil Gas Sampling in the Vadose Zone and Applications. In Management of Uncontrolled Hazardous Waste Sites Proceedings, Hazardous Materials Control Research Institute,Washington, D.C., 1984. 

This property can be applied to the detection of substances that absorb in the UV region For on layers containing a fluorescent indicator or impregnated with a fluorescent substance the emission is reduced in regions where UV-active compounds partially absorb the UV light with which they are irradiated. Such substances, therefore, appear as dark zones on a fluorescent background (Fig. 4A). 

For the detection of ampicillin it is necessary to add acetic acid to the dipping or spray solution. Ampicillin then yields pale zones on a blue background [2]. 

In five pilot plants that can be used to simulate the route of anionic surfactants from the consumer via the effluent purification plant to the receiving water, possible toxic effects of residual surfactant content and breakdown products of the secondary alkanesulfonates were investigated [102]. As indicators of the effects on living organisms of the effluent in the receiving water, flora and fauna that are frequently encountered in the p-mesosaprobic zone were used as models. The embryo-larval test was also employed as an additional method for the detection of toxic compounds in the water. 

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. 

Note Primary amines yield fluorescent chromatogram zones even before the application of reagent 3. Secondary amines do not yield fluorescent derivatives until they have been treated with reagent 3. Hence, the reagent sequence allows the stepwise detection of primary and secondary amines. Taurine is preferred as the essential component of reagent 3 over the multiplicity of other possibilities because it produces intense fluorescence it is also not very volatile and is readily available. Amides and substances with peptide linkages, eg. hippuric acid, are not detected, neither are secondary amines that are volatile at high temperatures. 

Note The contrast between the colored zones and the layer background can be improved by warming the chromatogram gently [4]. Di-tert-butyl peroxide does not react [3]. N,N,N, N -tetramethyl-p-phenylenediamine (q.v.) can also be used instead of N,N-DPDD for the detection of peroxides [3]. The spray solution for peroxides gradually turns dark red in color but it still retains its ability to react for several weeks [4]. 

This generally produces red-brown to blue-violet chromatogram zones on a sand-colored background. The detection of antibiotics with spray solution III yields almost colorless chromatogram zones on a blue background [4, 5]. 

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