Layers polyamide

The reagent can be employed on silica gel, kieselguhr. Si 50 000, NHi, cellulose and polyamide layers. 

Note Aldoses other than glucose can also be used e.g. arabinose [1], xylose [2, 3, 7] or ribose [4]. The background color is least on cellulose layers when cellulose acetate, aluminium oxide 150, silica gel, RP, NH2 or polyamide layers are employed the background is a more or less intense ochre. The detection limit of carboxylic acids on cellulose layers is ca. 0.5 pg substance per chromatogram zone. 

Note The reagent can be employed on silica gel, kieselguhr, RP and, with lower sensitivity of detection, on cellulose layers. The color differentiation is probably greater on cellulose layers [1]. A dark blue background is produced on polyamide layers. 

Although the reagent itself is not fluorescent an excess of NBD-chloride can interfere in quantitative analysis. In such cases it should be checked whether prechromatographic derivatization produces better results [3, 4]. The reaction products can then be separated on polyamide layers. 

Note Silica gel, kieselguhr and polyamide layers can be used as stationary phases. Not all acids are stained on RP layers. Amino layers yield a pale blue background. The detection limits are in the pg range for carboxylic acids [1], thioglycolic and dithioglycolic acids [2] and for antithyroid pharmaceuticals [4] they are about 5 ng per chromatogram zone for sterols and steryl esters [6]. 

Note The dipping solution can also be sprayed on. The detection of the aromatic acids is best performed on cellulose layers, if ammonia-containing mobile phases have been employed. The reagent can also be employed on silica gel, aluminium oxide, RP 18 and polyamide layers. 

The reagent, which can also be employed to impregnate the layer before chromatography, is best suited for silica gel layers [4] it can, however, also be employed on aluminium oxide, kieselguhr. Si 50000, cellulose and polyamide layers [4]. 

Iodine is a less suitable reagent for use on moderately polar phases and RP materials. The chemical modification of the silica gel that such layers have undergone makes them considerably more lipophilic, so that the contrast between substance-coated chromatogram zone and substance-free background is not very strong. The same applies to polyamide layers. 

The reagent can be used most advantageously on aluminium oxide, silica gel, kieselguhr. Si 50000, cellulose, diol and water-wettable RP 18 layers there is less contrast in color on strongly hydrophobic RP 18 phases. NH2 and polyamide layers are not suitable because the iodine is too strongly bound and the whole layer is colored green-yellow. 

The reagent can, for instance, be employed on silica gel, kieselguhr. Si 50000, cellulose and NH2 layers the reaction is appreciably less sensitive on RP 18, CN and Diol phases, neither is there any color differentiation of the purine derivatives [8J. Cellulose and polyamide layers are not suitable, since the whole layer background is colored dark brown [8]. 

The detection limits for compounds with P=S double bonds are lower than those for substances with single P—S bonds [7]. They are lower on silica gel than on polyamide layers [15] and are, for instance, 10-20 ng substance per chromatogram zone for... 

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. 

---