Ammonia Vapor Reagent

The chromatograms are dried in a stream of warm air, then sprayed homogeneously with reagent 1 and heated to 180°C for 30 to 45 min. After cooling to room temperature they are homogeneously sprayed with reagent 2 and then exposed to ammonia vapor (reagent 3). 

Ammonia Vapor Reagent Ammonia Vapor Reagent 169... 

Detection and result The chromatogram was freed from mobile phase in a stream of cold air, conditioned for 15 min in ammonia vapor (placed in a twin-trough chamber whose second part contained 25% ammonia solution). It was then immediately immersed in the reagent solution for 1 s and heated to 180 °C for 15 min. 

The dried chromatogram is first dipped in reagent solution 1 for 1 s, dried briefly in a stream of cold air and then dipped in reagent solution 2 for 1 s. The TLC/HPTLC plate is then held upright on tissue paper to allow excess reagent to drain away when the layer appears matt it is covered with a glass plate and kept at room temperature for 5 min. Afterwards it is dried in a stream of hot air and exposed to ammonia vapor. 

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. 

Table 1 Absorption maxima and detection limits for some 2,6-dinitroaniline herbicides on silica gel layers after treatment with the reagent sequence and after additional exposure to ammonia vapor.

Fig I Chromatogram of 2,6-dinitroaniline herbicides after treatment with the reagent sequence (A) and after additional treatment with ammonia vapor (B) 1 = oryzalin, 2 = nitralin, 3 = dinitramin, 4 = pendimethalin, 5 = butralin, 6 = fluchloralin, 7 = isopropalin, 8 = trifluralin, M = mixture. 

Reagent 3 Ammonia vapor Concentrated anunonia solution in the free trough of a twin-trough chamber. 

Note The TDM reagent can be used everywhere, where o-tolidine is employed. It can also be used on chromatograms, that have already been treated with ninhydrin, Pauly or ammonia perchlorate reagent or with iodine vapor [1]. Water may be used in place of 80% 2-propanol when making up solutions II, III and IV. The chlorine gas atmosphere in the chromatography chamber can also be created by pouring 5 ml hydrochloric acid (ca. 20%) onto 0.5 g potassium permanganate in a beaker such a chlorine chamber is ready for use after 2 min. 

Detection and result The chromatogram was dried in a stream of warm air for 10 min, immersed in the reagent solution for 2 s, briefly dried in a stream of warm air and heated to 110°C for 2 min. After cooling to room temperature it was then exposed to ammonia vapors for 5 min (5 ml ammonia solution in the empty trough of a twin trough chamber). 

Note The reagent can be just as successfully employed on silica gel, kieselguhr, aluminium oxide and polyamide layers as it can with RP and NH2 phases. The final treatment with ammonia vapor to decolorize the background can be omitted in the last case. 

Phenols can be detected with diazotized orthanilic acid or dianisidine by spraying an ammoniacal silver nitrate solution, followed by exposure to ultraviolet light, or with a modified ferric ferricyanide reagent, and also by exposing the wet layer successively to nitrogen dioxide and ammonia vapors. 

Iodine vapor allows nonspecific, usually nondestructive detection of many sub-stances (e.g. surface active agents [129], pharmaceuticals [130, 131], polyethylene glycols [132], see also Table 12). In addition, reactions have also been described with the vapors of bromine [133—135], cyanogen bromide [136], chlorine [137-141, 209], ammonia [147-147] (see also the reagent Ammonia vapor ). 

Detection and result The chromatogram was freed from mobile phase and ammonia vapors and immersed twice for 10 s in reagent solution, with intermediate drying in a stream of cold air, and then heated to 95°C for 12 min. The steroid - derivatives were then visible under long-wavelength UV light (A - 365 nm) as light... 

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