Universal reagents

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... 

Iodine is such a universal reagent. It was introduced by Mangold [i] as early as 1961 for the analysis of lipids and used again within a year by Bakrett [2] as a nondestructive reagent . 

Note Like sulfuric acid (q.v.) ort/io-phosphoric add is a universal reagent, with which almost all classes of substance can be detected at high temperatures (150-180 °C) by charring e.g. high molecular weight hydrocarbons (mineral oils) [20]. The colors and fluorescences produced at lower temperatures (<120°C) and their intensities are very dependent on the temperature and period of heating. It is not possible to use meta- or pyrophosphoric acid in place of or/Ao-phosphoric add, since, for instance, amanita toxins react well with alcoholic phosphoric add only weakly with aqueous phosphoric add and not at all with meta- or pyrophosphoric acid [17]. 

Umbelliferone, pH-dependent change of fluorescence color 44 Universal reagents 4,46,195,376,402,405, 412, 430, 434 Uracil derivatives 44,45 Uranium cations 144 Uranyl acetate reagent 44 Urea... 

The separation of uncolored samples is usually done on TLC plates containing a fluorescent dye so as to use the fluorescence-quenching effect for sample location. If such plates are not available or if samples show no quenching effect, two universal reagents can help. If the TLC plate is simply sprayed with water, sample spots are very often not translucent but white. Clearer zones can be obtained sometimes by first saturating... 

Sulfuric acid in combination with MnCl2 is often used as an universal reagent. Two-hundred mg of MnClj THjO have to be dissolved in 30 ml of water and must be subsequently diluted with 30 ml of methanol. Finally, 2 ml of concentrated H2SO4 mnst be added carefully. After spraying, 15 min of heating at 120°C is necessary to complete the reaction. Organic compoimds form brown spots on a white background [17]. 

In 1994, the Dako Corporation introduced its Envision system (10). This immunoenzyme technique achieves both sensitivity and speed in a universal reagent. The secondary antibodies (derived from goats, in the case of the per-... 

Rao, N.S., Agarwal, S.K., Chauhan, V.K., Bhatia, D., Sharma, A.K. et at, Microwave-assisted spectropho-tometric estimation of polymer-supported functional groups using a universal reagent, Anal. Chim. Acta, 2000, 405, 247. 

Nagy, A. (2000) Cre recombinase the universal reagent for genome tailoring. Genesis 26, 99-109. 

EPOS, which contained primary antibodies, the EnVision system contained secondary antibodies with anti-mouse Ig and anti-rabbit Ig specificity. This universal reagent could be used to detect any tissue-bound primary antibody of mouse or rabbit origin. The utility of this method opened the door to a new family of polymer-based immunohistochemical methods. The sensitivity of these methods compared to LSAB and ABC methods was comparable or even slightly greater in most cases (7). With the latest development of EnVision FLEX+ the sensitivity has been improved even further. However, because of the large molecular size of the polymer conjugates, accessibility to certain epitopes was restricted, presumably due to steric hindrance, in a minority of cases. 

Vaskovsky VE, Kostetsky EY, Vasendin IM (1975) A universal reagent for phospholipid analysis. J Chromatogr 114 129-141... 

Oxazolines are usually formed from an amido alcohol by cyclization with a dehydrating reagent. There does not seem to be a universal reagent that serves all situations. Some of the reported methods are as follows. The section on the protection of acids as oxazolines should be consulted. 

Note Anisaldehyde — sulfuric acid is a universal reagent for natural products, that makes color differentiation possible [6]. The background acquires a reddish... 

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