Aromatic chromatogram

Chromatograms do not give a sharp differentiation between aromatics and resins. 

Fluorescence scanning of chromatograms of polycyclic aromatic compounds is a vivid example of their employment. A careful choice of the wavelengths of exci-... 

Fig. 42 Chromatogram of polycyclic aromatic hydrocarbons on caffeine-impregnated precoated silica gel 60 HPTLC plates with concentrating zone (Merck). The following can be recognized in increasing Rf value. — 1. benzo(ghi)perylene, 2. indeno(l,2,3-cd)pyrene, 3 benzo(a)pyrene, 4. benzo(b)fluoranthene, 5. benzo(k)fluoranthene, 6. fluoranthene.

Note Note that the diazotization of primary aromatic amines can also be achieved by placing the chromatogram for 3 — 5 min in a twin-trough chamber containing nitrous fumes (fume cupboard ). The fumes are produced in the empty trough of the chamber by addition of 25% hydrochloric acid to a 20% sodium nitrite solution [2, 4], iV-(l-Naphthyl)ethylenediamine can be replaced in the reagent by a- or -naphthol [10, 14], but this reduces the sensitivity of detection [2]. Spray solutions Ila and lib can also be used as dipping solutions. 

In the case of carbohydrates blue chromatogram zones are produced on a yellow background that slowly fades [2]. Steroids, vitamins, antioxidants, phenols and aromatic amines yield, sometimes even at room temperature, variously colored chromatogram zones [5]. -Blockers and laxatives also acquire various colors [7, 10]. The detection hmits are in the nanogram to microgram range [5]. 

Figure 14.15 Typical SFC chromatogram of total olefins in gasoline 1, saturates 2, aromatics 3, olefins t(L), time of loading sample on to columns and eluting saturates t(AR), time of eluting aromatics t(C), time of eluting remaining saturates from olefin trap t(BF), time of eluting olefins by back-flush.

Figure 14.19 Typical GC chromatogram of the separated di-aromatics fraction of a middle distillate sample Peak identification is as follows 1, naphthalene 2, 2-methylnaphthalene 3, 1-methylnaphthalene 4, biphenyl 5, C2-naphthalenes 6, C3-naphthalenes 7, C4-naph-thalenes 8, C5+-naphthalenes 9, benzothiophene 10, methylbenzothiophenes 11, C2-ben-zotliiopIrenes. Note the clean baseline between naphthalene and the methylnaphthalenes, which means that no overlap with the previous (mono-aromatics) fraction has occuned.

Phillips and Xu have presented two-dimensional (2D) chromatograms of kerosines, separated with different stationary phase combinations, in many thousands of components (37). Frysinger et al. have separate benzene-toluene-ethyl benzene-xylenes (BTEX) and total aromatics in gasolines by using GC X GC... 

Chromatograms demonstrating the simultaneous use of all three detector functions are shown in figure 22. It is seen that the anthracene is clearly picked out from the mixture of aromatics by the fluorescence detector and the chloride ion, not shown at all by the UV adsorption or fluorescence detectors, clearly shown by the electrical conductivity detector. 

The oxidized aromatic amines yield yellow-colored chromatogram zones on a colorless background. 

For example, ergot alkaloids produce without exception blue chromatogram zones, while clavine alkaloids primarily produce green colors [4], Urea derivatives and primary aromatic amines yield yellow chromatogram zones [28,33,34,36,37] and PR toxin and PR imine emit intense blue fluorescence on excitation with long-wavelength UV light (X = 365 nm) [44],... 

The detection limits per chromatogram zone are 1-3 pg substance for ergot alkaloids [9], 5 pg for diuretics [11] and 5-30 ng for aromatic amines [5]. 

The visual detection limits for aromatic amines and phenols are 100-600 ng substance per chromatogram zone [1 -3]. 

Variously colored chromatogram zones appear, some before heating, on a colorless background [1] those produced by aromatic o-diamines are excited to fluorescence by long-wavelength UV light (X = 365 run) [2]. 

The chromatogram is freed from mobile phase, lightly but homogeneously sprayed with the spray solution or immersed in the dipping solution for 2 s. Triazines and aromatic amines must first be converted to chlorinated derivatives by exposing the chromatogram to chlorine gas (see Procedure Tested ). 

After a few minutes drying in air sterol hydroperoxides, nitrate esters, triazines and aromatic amines yield blue-violet chromatogram zones on a pale blue to violet background [1, 3]. Polynitroaromatics yield yellow to dark beige zones [3]. 

Note The chromatogram zones exhibit a broad spectrum of colors [3, 12] that is very dependent on the duration and temperature of heating. Therefore the optimum reaction conditions must be determined empirically. With a few exceptions (ferulic, 4-amino-benzoic and cumarinic acids) aromatic carboxylic acids do not react [3]. The reagent in 80 ethanolic sulfuric acid is reported to be most sensitive for steroids [25]. 

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