Paraffins hexane

Detection and result The chromatogram was freed from mobile phase and dipped for 1 s in solution I and after drying for 1 min in a stream of cold air it was dipped in a solution of liquid paraffin — -hexane (1 + 2) in order to stabilize and increase the intensity of fluorescence by a factor of 1.5—2.5. The derivatives which were pale yellow in daylight after drying fluoresce pale blue to turquoise in long-wave... 

The fluorescence intensity of the chromatogram zones could be stabilized and increased by a factor of 2.5 to 3.5 by subsequent immersion in liquid paraffin — -hexane (1 + 2). 

Note If the chromatogram developed by method B was exposed to ammonia vapors for 10 min before being immersed in liquid paraffin— -hexane (1 -I- 2) the fluorescence of the chromatogram zones became deep red. Glucose and fructose also appeared red. 

Note A 5% solution of polyethylene glycol 4000 in ethanol can be sprayed onto the chromatogram [2, 4] for the purpose of increasing and stabilizing the fluorescence instead of dipping it in liquid paraffin - -hexane (1 - - 2). If this alternative is chosen the plate should not be analyzed for a further 30 min since it is only then that the full intensity of the fluorescence develops [6]. 

In situ quantitation For fluorimetric evaluation there was excitation at = 313 nm and the fluorescence emission was measured at = 365 nm (monochromatic filter M 365). This arrangement yielded the most intense signals. (The emission beam at X, = 365 nm is appreciably more intense than the visible yellow fluorescence.) Further treatment of the chromatogram with liquid paraffin - -hexane (1+2) is not to be recommended. 

Note In the case of aryl- and heteroarylpropionic acids the chromatograms are irradiated with unfiltered UV light for 30 min before application of the reagent [5], The chromatograms can then be immersed in a solution of liquid paraffin - -hexane (1-1-2) in order to stabilize and enhance the fluorescence [5]. 

Detection and result The chromatogram was dried in a stream of warm air for 15 min, cooled and immersed in the reagent solution for 2 s. It was then heated to 110—120°C for 10—20 min, allowed to cool to room temperature and immersed for 2 s in liquid paraffin — -hexane (1 - - 6) to enhance and stabilize the fluores-... 

On account of the noisier background the detection limits for fluorimetric determination were twice as high as those for reflectance determination where they were 5 ng substance per chromatogram zone. An additional immersion in liquid paraffin - -hexane (1 + 2) did not lead to an intensification of the fluorescence. 

The result was that light blue fluorescent zones were visible under long-wavelength UV light (A = 365 nm). Before fluorimetric analysis the chromatogram was dipped for 1 s into liquid paraffin — -hexane (1 + 2) to enhance (by a factor of 2 to 8) and stabilize the intensity of the fluorescence and then dried for 1 min in a stream of cold air. The quantitation (Ae,c = 365 nm Afi > 430 nm) was carried out after 1 h since it was only then that the fluorescence intensity had stabilized. 

The color shades of the chromatogram zones and above all the pale background produced by this technique are stabilized by dipping the chromatogram in a solution of liquid paraffin — -hexane (1-1-2) for 2 s. The color shades produced on silica gel and RP layers are not identical. 

Detection and result The chromatogram was heated in the drying cupboard to 110 —120 °C for 25 min and immediately placed - while still hot - in a twin-trough chamber, whose second trough contained 10 ml 25% ammonia solution, for 15 min. The chromatogram was then immersed for 2 s in a solution of liquid paraffin - -hexane (1 + 2). 

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