Universal detection reagents

J. Sessler etaU US Patent 6,482,949 (November 19, 2002) Assignee Board of Regents, University of Texas System Utility Analytic Reagents for Detection of Fluoride, Chloride, and... 

A. Iodine The universal detection reagent iodine is used either as a 1% alcoholic spray, or the plate is placed in a closed jar or tank containing iodine crystals. The iodine vapor dissolves in, or forms weak charge-transfer complexes with organic compounds, which show up as brown spots on a pale yellow background within a few minutes. After marking zones for future reference, exposure of the plate to air causes the iodine to sublimate and the spots to fade, after which the plate can be sprayed with another reagent or the solute can be eluted from the plate for further analysis. 

Stein and Moore, 1948) and the use of ninhydrin as a universal reagent for detecting and quantifying amino acids both manually and automatically (Moore and Stein, 1948). 

Scorilas A, Diamandis EP (2000) Polyvinylamine-streptavidin complexes labeled with a europium chelator a universal detection reagent for solid-phase time resolved fluorometric applications. Clin Biochem 33 345-350... 

Detection is carried out with cerium (IV) stdphate (Bgt. No. 37). It cannot be used with layers impregnated with silver nitrate, nor with alumina layers. Iodine vapour or solution (Rgt. No. 143) or para-formaldehyde-phosphoric acid (Rgt. No. 194) can be used also and 2,4-dinitrophenylhydrazine (Rgt. No. 82) with alkaloids containing a keto group. The cerium (IV) sulphate reagent is recommended as a universal detection agent zl -unsaturated compounds yield a colour reaction even in the cold. Iodine vapour permits non-destructive detection of the sterol alkaloids, so that they may be subsequently isolated unchanged. 

It is important to understand that evidence from TLC alone is not sufficient for unambiguous identification of unknowns. Correspondence of / . values between sample and standard zones provides only presumptive identification, and non-universal detection reagents are not specific for one compound but selective for a type or class of compounds. Combined methods (Section B) must be used for increased certainty. 

Detection is most simple when the compounds of interest are naturally colored or fluorescent or absorb ultraviolet (UV) light. However, application of a location or visualization reagent by spraying or dipping is usually required to produce color or fluorescence for most compounds. Absorption of UV light is common for many compounds, e.g., aromatics and those with conjugated double bonds. This leads to a simple, rather universal detection method on layers impregnated with a fluorescence indicator (fluorescence quench detection). 

In spite of numerous advances in the field of detection there are not and never have been any genuinely substance-specific chemical detection reactions. This means that, unlike the spectrometric methods, the methods of detection normally employed in chromatography cannot be employed for an unequivocal identification of compounds, they can only provide more or less definite indications for the characterization of the separated substances. Universal reagents are usually employed for a first analysis of the separation of samples of unknowns. This is then followed by the use of group-specific reagents. The more individual the pieces of information that can be provided from various sources for a presumed substance the more certainly is its presence indicated. However, all this evidence remains indicative it is not a confirmation of identity. 

Microchemical reactions These can be carried out either with universal reagents [11] or with such substances which react with particular functional groups (group-characterizing reagents). If the separation process ensures that only one component occurs at a particular spot on the chromatogram, then this can be detected sub-stance-specifically . But specificity in an unequivocal sense can only be produced by a combination of the separation and the detection process. (The same is true of other forms of detection.)... 

Note Rhodamine B is a universal reagent that can be used on silica gel, talc, starch [5] and cellulose layers, just as on urea [1] or silver nitrate-impregnated [7] phases. Liquid paraffin-impregnated silica gel and RP layers are less suitable, since the background to the chromatographic zones is also intensely colored. It is often possible to increase the detection sensitivity by placing the plate in an atmosphere of ammonia after it has been sprayed or dipped, alternatively it can be oversprayed with sodium or potassium hydroxide solution. 

Note Rhodamine 6G is a universal reagent which can also be incorporated in the TLC layers [4, 9] or added to the mobile phase [4], The spray reagent can also be made up in water [8], acetone [4, 6] or ammonia solution (c = 2.5 mol/1) [5]. The visual detection limit is most favorable when the water from the mobile phase or the detection reagent has not completely evaporated from the layer. This can be recognized by the fact that the background fluorescence has not turned from red to pink [4]. 

Note Sulfuric acid is a universal reagent, with which almost all classes of substance can be detected by charring at elevated temperatures (150—180°C). The production of colored or fluorescent chromatogram zones at lower temperature (< 120 C) and their intensities are very dependent on the duration of heating, thf... 

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