Rf values relative

Mortimer86 has also recommended the two-dimensional method, using ethyl acetate-acetic acid-water and ethyl acetate-formamide-pyridine as developers. Methyl Cellosolve-ethyl methyl ketone-ammonium hydroxide may also be used. Since high content of water and the presence of an alcohol in the solvent mixture gave rise to diffuse spots, formamide was substituted for water. RF values relative to the movement of orthophosphate were determined and found to vary with the distance the solvent moved. Also, in complex mixtures, the presence of some esters resulted in elongation of other ester spots. This effect and the RF variation observed-do not conform to the concept of a liquid-liquid distribution process. 

H2TAPP is a purple-black microcrystalline compound that is a mixture of four atropisomers (see below). Tic on silica (1 1 benzene/diethyl ether) shows four spots Rf values (relative intensity) 0.77 (1), 0.64 (2), 0.43 (4), 0.04 (1). It is quite soluble in organic solvents with the exception of alcohols and saturated hydrocarbons. max(CHCl3) 418,517,550, 589,645 nm. 

Labeled compounds were applied as spots on STLC plates and developed with distilled water by ascending chromatography. The developed plates were exposed to Kodak Royal Blue X-ray film for 2 to 3 weeks. The Rf value (relative frontal movement) for each compound was measured as the front of the spot or streak in the resultant autoradiogram (30). 

An alternative approach which minimises differences in Rf values due to the influence of the variables enumerated above, is to quote the Rf value relative to a carefully chosen standard which is run on the same plate. This relative value R, should be constant since under any given conditions the relative Rf values remain the same. 

Internal standardisation. A second method of standardisation uses an internal standard as a marker. A known amount of the standard is added to a standard mixture of all the components to be analysed and the Z)rf values relative to the internal standard calculated. The accurate amount of internal standard is then added to each sample and the sample analysed. The amount of each component is then calculated using the equations below (a more detailed account is given in section 2.7) ... 

Vitride reagent (0.5 mL) is added to the lipid (1 to 10 mg) in diethyl ether-benzene (2.5 mL 4 1, v/v) in a test-tube, and the solution is heated with occasional shaking for 30 min at 37°C. On cooling, water-ethanol (10 mL 5 1,v/v) is added cautiously, then the products are extracted with diethyl ether (3 x 6 mL portions) hexane (10 mL) is added and the solution is dried over anhydrous sodium sulfate. After filtering, the solvent is removed from the combined extracts in a rotary evaporator. The samples are dissolved in a little chloroform and applied to a silica gel G TLC plate, which is developed in diethyl ether-hexane (4 1, v/v). The products are identified by their Rf values relative to standards, alkyl ethers migrating just ahead of the alk-1-enyl analogues, and they are eluted from the adsorbents with several volumes of diethyl ether."... 

Fig. 60 Chromatogram of a 6 dyestuff mixture made up (according to falling Rf values) of Sudan red 7B, Sudan orange G, Sudan black B, Sudan yellow, Artisil blue 2RP and Sudan black B (2 components) under different humidity conditions. From left to right 72, 65, 47, 42, 32,18, 14 and 9% relative humidity layer silica gel 60 mobile phase toluene.

TLC Analysis. Samples were examined by TLC using standard procedures. Rf values were determined and compared with those of authentic reference materials. Radioactive components were located by scanning (Vanguard Instrument Corp., North Haven, Conn., Model 885) or by autoradiography (Eastman Kodak, Rochester, N. Y., type AA film). The relative Rf value of DCDD on silica gel plates (Brinkmann Instruments, Inc., Westbury, N. Y., type For,4) when developed with n-hexane dioxane acetic acid, 90 10 4, V/V/V, was 0.90. The observed impurity had a relative Rf value of 0.40. On Brinkmann alumina plates, developed with n-hexane, DCDD had a relative Rf of 0.32. Neither system separated the chlorinated dibenzodioxin isomers. 

Qualitatively equation (7.15) is adequate to describe tiM f influence of layer quality, selectivity, and zone position in the 1 chromatogram upon resolution for a single unidimensional development under capillary flow controlled conditions. The variation of R, with Rf is not a simple function as can be seen from Figure 7.6. The resolution increases with the layer efficiency in a manner that depends linearly on the R, value. — Relatively small changes in selectivity have an enormous impact on... 

Basically, the Rf value of a solute is determined by its distribution ratio which in turn is dependent on relative solubilities for partition systems or relative polarities for adsorption systems. For example, if adsorption TLC is used to separate a mixture of squalene (a hydrocarbon), methyl oleate, cholesterol and a-tocopherol (vitamin E), then squalene, being the least polar, will move furthest and the cholesterol, being the most polar, will remain close to the origin. Methyl oleate is less polar than a-tocopherol and will therefore be found between it and the squalene. The role of polarity is discussed more fully on p. 82. 

Calculate the Rf values of each compound and comment on the relative values. 

TLC, using silica gel GF 254 plates, can separate halcinonide from its synthetic precursors (of. section 1.5). Using a developing solvent of chloroform-ethyl acetate (5 1), the following Rf values were found Dihydrotriamcinolone, Rf = 0.0 dihydrotriamcinolone ace-tonide, Rf = 0.08 dihydrotriamcinolone acetonide-21-mes-ylate, Rf = 0.18 and halcinonide, Rf = 0.36. Continuous TLC development gives respective relative Rf values of 0.02,... 

Infrared spectra were obtained with a Perkin-Elmer 1800 and a Nicolet Magna-IR 750 FTIR spectrophotometer, and the absorption frequencies are reported in wave numbers (cm4). NMR spectra were obtained with BZH-300 and CA-F-300 Bruker FTNMR 300 MHz spectrometers. Chloroform-d was used as solvent, and all chemical shifts are reported in parts per million downfield (positive) of the standard. H-NMR and 13C-NMR chemical shifts are reported relative to internal tetramethylsilane, while 19F-NMR chemical shifts are reported relative to internal fluorotrichloromethane, Rf values were obtained from silica gel thin-layer chromatography developed with a mixture of 1.5 mL methylene chloride and three drops of acetone. The number of hydrate water molecules was calculated from the integration of H-NMR spectra. 

Observations In the chromatogram obtained with solution (1), there is no reddish orange spot with an Rf value of 0.3 to. 5 relative to the principal spot (about 2% of morphine). The test in not valid unless there is a clearly visible spot in the chromatogram obtained with solution (2). 

Relative mobility (Rf - value) for each sample is given FMOC = precolumn derivatization with FMOC-Cl, unident. = unidentified peak, not sign. = not significant peak, - = no fluorescent peak, DHLNL = dihydroxylysinonorleucine, HAL = histidinoalanine, HP = hydroxylysylpyridinoline, LAL = lysinoalanine. 

In the TLC of the toxins (lower part of Figure 5), Rf values are not presented because they show small variations and are potentially misleading. However, the relative elution sequence has proven to be highly reproducible, such that the two-dimensional composition maps produced by this method can be interpreted with a high level of confidence. 

The Rf Value Ry value is the relative rate of solute and solvent. 

It is not difficult to determine a solvent composition which has a high minimum resolution, once it has been determined what temperature and relative humidity should be used. Suppose, for example, that a temperature of 20 °C and relative humidity of 40% have been selected, then it is possible to predict the Rf values and thus the resolutions between the solutes for all solvent compositions. Since there are seven solutes, there are six resolutions. The minimum resolution is the lowest of these values. The problem is now... 

Note The term Rf values refers to a relative rate of movement of the test sample through the chromatographic column... 

It was seen that irrigating solvent had pronounced effect on the relative mobilities of the n complexes eg the Rf values of Tetryl and Picramide. were reversed with petroleium ether—ethyl acetate (9 1) compared to MCB-EDC system ... 

Thin-layer Chromatography (Rf values) of Natural,. V,0-Acylated Sialic Acids and of the C, and C8 Analogs of Neu5Ac and Neu5Gc in System A" and in Gas-Liquid Chromatography (fiT Values, Relative to Neu5Ac = 1.00) in Systems B and C ... 

Another approach to the TLC separation of linear and branched polystyrenes was reported by Belenkii etalThe adsorbent used was silica gel with a mean pore diameter of 80 A (notice that no molecular sieving mechanism should be operative in this pore diameter), and the developer was composed of cyclohexane, benzene, and acetone in a composition of 12 4 y, where 7 is the relative amount of acetone added. The TLC experiments were performed for different 7 values ranging from 0.4 to 1.5. With increase in the 7 value, the Rf values increased both for the linear and branched samples but the dependence for the linear samples was remarkably stronger than for the branched ones. 

In TLC each component is defined by its Rf value (retardation factor) that corresponds to its relative migration compared to the solvent ... 

El 2. Predict the relative order of paper chromatography Rf values for the amino acids in the following mixture Ser, Lys, Leu, Val, and Ala. Assume that the developing solvent is iz-butanol, water, and acetic acid. 

B 3. Try to explain the relative order of Rf values you obtained for the standard lipids. 

Figure 25-3 Idealized two-dimensional paper chromatogram of a mixture of amino acids. The horizontal and vertical scales represent the distance of travel of a component of the mixture in a given solvent relative to that of the solvent itself. This is known as the R, value and is fairly constant for a particular compound in a given solvent. A rough identification of the amino acids present in the mixture may therefore be made on the basis of their Rf values.

Table IV shows the Rf values for all the gibberellins except A2, on paper and in four different solvent systems. The gibberellins are arranged in order of increasing mobility (in fact, in increasing number of hydroxyl groups). The relative mobilities (R.M.) in brackets are given to compare with relative mobilities derived from published Rf values for unidentified gibberellin-like materials.

The behavior of GA3 is anomalous in the presence of plant extracts, particularly at low relative concentrations of GA3. Not only are the Rf values altered and the band shapes distorted, but often the GA3 completely fails to respond to the detection test. Although the major causes for this behavior are undoubtably over-... 

Provided that the experimental conditions are reproducible the movement of any substance relative to the solvent front in a given chromatographic system is constant and characteristic of the substance. The constant is the RF value and is defined as ... 

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