Ammonia background

This detector is a handheld ion mobility spectrometer using ammonia as dopant to permit operation under an ammonia background. 

For the increase of sensitiveness of the voltamperometric determination Co(II) use o,o -dihydroxysubstituted azodyes (eriochrome red B and calces). The Co(II) determination can be conducted at potential of reduction of coordinating connection of Co(II)-azodye (E = - 0,9V) and directly the Co(II) (E = -1,2V, ammonia buffer solution) ions. The results of reseaixhes show that selectivity of the Co(II) determination in presence the Ni(II) and Pd(II) ions more high with the use of analytical signal at the potential -1,2V. Is it thus succeeded move aside potentials of peaks of reduction of the Ni(II) and Co(II) ions on a background ammoniac buffer solution from AE=0,2V to AE = 0,4-0,5V. The Co(II) determination can be conducted in presence 50-100 multiple surpluses Ni(II). Palladium in these conditions does not prevent to 60 multiple surplus. 

Rather than dipping the chromatogram in acid solution it is preferable to heat it to 100°C for 2—5 min (fume cupboard ) in order to evaporate the ammonia and turn the background yellow. By this means it is possible to increase the sensitivity of detection for some of cations e.g. Sr and Ba. However, these zones fade after some time, so that it is necessary to quantify the chromatogram immediately after heating. 

Before treatment with ammonia valine (hRf 45 — 50), isoleucine (hRf 65 — 70) and leucine (hRf 70 — 75) produced red chromatogram zones and phenylalanine (hRf 55—60) violet chromatogram zones on a pale pink background. After treatment with ammonia all four amino acids appeared as violet chromatogram zones on a flesh-colored background these zones were stable over an extended period. 

Note If the spray solution or a nonbasic dipping solution is employed for detection then it is advisable to spray afterwards with a 10% aqueous solution of sodium carbonate or a 2% solution of borax in ethanol — water (1 + 1). It is often possible to achieve the required basicity by placing the chromatogram in a twin-trough chamber one of whose troughs contains 5 ml 25% ammonia. This is not suitable for the Chiralplate (Macherey-Nagel) because in this case the plate background acquires a dark violet coloration. 

Note Traces of ammonia left by the mobile phase should be completely removed from the chromatograms before the reagent is applied in order to avoid strong background coloration. The dipping solutions may also be applied as spray solutions. Secondary amines, amides, pyrimidines and purines do not react with the reagent [1]. In the case of benzodiazepines only those substances react which... 

Note Sulfuric acid (4%) can also be employed in place of hydrochloric acid [3]. If ammoniacal mobile phases are employed the ammonia should be removed completely (e.g. heat to 105 °C for 10 min) before dipping or spraying otherwise background discoloration can occur. The addition of titanium(III) chloride to the reagent allows also the staining of aromatic nitro compounds [6]. 

Detection and result The chromatogram was freed from mobile phase (NH3 ) in a stream of cold air for 45 min. It was then immersed in the dipping solution for 1 s and heated to 100°C for ca. 20 min. The chromatograms could be further treated with ammonia vapor if a colored background was found to be troublesome. The pale red zones then became bright red spots and the background frequently... 

Note Traces of ammonia from the mobile phase should be removed from the plate completely to avoid background discoloration (grey veil) [1]. If the layer is sprayed too heavily the initially grey-black chromatogram zones can fade again [2]. The reagent which is usually employed as a 1 to 2% solution [2, 3, 6, 7] can be treated with a few drops of nitric acid to clarify the solution [2]. 

Blue zones appear immediately or after a few minutes on a yellow background. The background can then be lightened [7] by placing the chromatogram in a twin-trough chamber whose second trough contains 25% ammonia solution. 

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 The background can be decolorized by spraying afterwards with 5% aqueous ammonia solution and/or 5 — 10% sodium thiosulfate in 50% aqueous ethanol [2, 3]. The sodium hydroxide may be replaced by potassium hydroxide in dipping solution 11 [4]. 

Nitroindole (ARf 40—45), 5-chloroindole (jiRf 60 — 65) and indole QiRf 70—75) yielded orange-yellow chromatogram zones on a pale yellow background. If the chromatogram was exposed to ammonia vapor for 15 s the color was intensified. The detection limits were 10 ng substance per chromatogram zone. 

There are two methods for overcoming these disadvantages. In the first the precipitation of silver cyanoargentate at the end point can be avoided by the addition of ammonia solution, in which it is readily soluble, and if a little potassium iodide solution is added before the titration is commenced, sparingly soluble silver iodide, which is insoluble in ammonia solution, will be precipitated at the end point. The precipitation is best seen by viewing against a black background. 

Nitrate and nitrite ions yield orange-brown to magenta-red chromatogram zones on a pale yellow background immediately on treatment with ammonia these zones are stable for days in an atmosphere of ammonia. 

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 This reagent sequence is a modiflcation of the reagent chlorine — potassium iodide — starch . Mobile phases containing ammonia must be removed completely before treatment with the reagent sequence, since otherwise the background will be colored too. Some secondary amines (e.g. diphenylamine) and some amides (e.g. 2,4-dinitrobenzamide) and methionine sulfoxide do not give reactions even in quantities of up to 1 to 2 (ig. 

Dimethylphenols yield turquoise-colored chromatogram zones on a violet background, that are converted to blue-violet zones on a flesh-colored background on brief exposure to ammonia vapor. 

Detection and result The chromatogram was dried for 10 min in a stream of warm air and immersed in the dipping solution for 2 s, dried for 2 min in a stream of warm air and heated for 1 min to 110°C (Thermoplate Desaga). 2,5-Dimethylphenol (hRj 25-30) and 2,6-dimethylphenol (h/Jj 40-45) appeared as turquoise-colored chromatogram zones on a violet background and were converted to blue-violet zones on a flesh-colored background on exposure to ammonia vapor for 5 min. 

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. 

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