Rf value, calculation

Rf values, calculated by dividing the distance moved by the water front by the distance moved by the compounds are given in TABLE V. These values can be used to verify various models. For... 

Table 1 Comparison of Experimentally Obtained Data with Two Different Mobile Phases with Rf Values Calculated According to Eqs. (1) or (2), Respectively...

Figure I6.10A shows a plot of In(/ 7" ) vs. for a film prepared from 400 nm diameter polypyrrole tubules [50]. The points are the experimental data, and the solid curve is the least-squares best fit line. The In(/ 7 ) data for this film show a dependence over a temperature range from about 256 to 20 K. These data indicate that 3D MVRH is appropriate for conduction in this film over this temperature range. To prove this point, we ratioed the measured resistance Rm) to the best-fit resistance (Rf) at each temperature. These data were then plotted as ln(Rm/Rf) vs. T, and, as indicated in Fig. 16.10B, this analysis was done using Rf values calculated using the 3D, 2D, and ID MVRH models. This analysis clearly shows that only the 3D model fits the experimental data for this sample. Identical results (i.e., 3D MVRH) were obtained for films prepared from 400 nm diameter polyaniline tubules [50]. The 3D model has been shown to be applicable to polypyrrole and polyaniline samples prepared by conventional synthetic methods [66-68].

The emission of the indicator is reduced in places where there are substance zones that absorb at 2 = 254 nm present in the chromatogram. This produces dark zones (Fig 4A), whose intensity (or rather lack of it) is dependent on the amount of substance applied. If the plate background is set to 100% emission the phosphorescence is reduced appropriately in the region of the substance zones. When the chromatogram is scanned peaks are produced, whose position with respect to the start can be used to calculate Rf values and whose area or height can be used to construct cahbration curves as a function of the amount applied (Fig. 25). 

Besides the calculation of the different sulfonated species, it is also possible to determine them directly by chromatographic methods. Separation of the ester sulfonate and the disodium salt is achieved by thin-layer chromatography on silica gel plates. With a solvent mixture of acetone and tetrahydrofuran (90 10 v/v) the disodium salt stays at the start whereas the ester sulfonate has an R value of 0.2. With the more polar solvent 0.1 N H2S04 + methanol + chloroform the ester sulfonate and the disalt have Rf values of 0.36 and 0.14. For visualization, the plate is sprayed with pinacryptol yellow. In UV light (254 and... 

Diffusion and mass transfer effects cause the dimensions of the separated spots to increase in all directions as elution proceeds, in much the same way as concentration profiles become Gaussian in column separations (p. 86). Multiple path, molecular diffusion and mass transfer effects all contribute to spreading along the direction of flow but only the first two cause lateral spreading. Consequently, the initially circular spots become progressively elliptical in the direction of flow. Efficiency and resolution are thus impaired. Elution must be halted before the solvent front reaches the opposite edge of the plate as the distance it has moved must be measured in order to calculate the retardation factors (Rf values) of separated components (p. 86). 

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

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. 

Figure 3.4 Thin-layer chromatography. Rate of flow (RF) for the analyte indicated is x/y. The Rf values for the other components can be calculated in a similar manner, the value y being the same in each case.

The measurement of effluent volume is not very reliable because of the effect of the geometry and packing characteristics of any column. It is often more useful to use a reduced parameter, such as V/V0, which is not so dependent upon column characteristics and is comparable with the calculation for RF values in thin-layer chromatography. 

The independent determination of molecular masses by SDS-PAGE is impossible. To estimate the molecular mass of a protein, measure the path of that protein or calculate its Rf value (distance of the protein from origin/distance of electrophoresis front from origin) and compare these values with that of marker proteins, i.e., proteins with independently determined molecular masses. This method is successful only if the protein of interest behaves regularly in SDS-PAGE, i.e., it is totally unfolded by SDS, has a rod-like shape, and the SDS/protein ratio is the same for the unknown and the marker protein. Especially highly hydrophobic proteins and glycoproteins often deviate from these assumptions. 

This value is related to Rp, the thermodynamic Rf value. This latter value describes the equilibrium between the solute in the solvent and adsorption on the stationary phase. The relation between Rf and Rf is RJ= Rf is a constant which depends on several factors. When the stationary phase is pre-loaded with solvent molecules from the gas phase is about 1.1. Based on the Rf several other characteristics can be calculated. These are the capacity factor ... 

Prepare a table of Rf values for the standard amino acids. You should also describe the color of the original ninhydnn spot. Since the colors vary slightly with the amino acids, this aids in the identification of an unknown amino acid. Calculate the Rf values for the constituent amino acids of the unknown peptide. From these data you should be able to identify the amino acids present in your unknown. 

Calculate the approximate percentage lipid composition of the nutmeg (assume the lipid recovery is quantitative). Prepare a table listing the Rf values obtained for each standard lipid and for the crude and purified unknown. By comparing R values, identify the general class of lipid to which your purified extract belongs. How effective was your purification step If... 

The RF should be determined using standards at various concentrations, and an average RF value should be used in the calculation. Both the external standard and internal standard calibration methods for GC analysis are fully discussed in Chapter 1.3. 

Miller and Kirchner (173) have developed an analytical method for volatile constituents including camphor. They used silicic acid coated-glass chromatostrips. Ethyl acetate hexane, chloroform, benzene, isopropyl ether and their mixtures were used as developers and the strips were examined with various reagents like bromine, fluorescence, 0-anisidine, Sulphuric acid - nitric acid, and concentrated sulphuric acid. The Rf values were calculated. 

El-Deeh, et al (175) have reported the separation and evaluation of camphor by TLC technique on silicic acid plate.The behaviour of camphor on chromatoplates was studied using different solvents of increasing polarity and their mixtures as developers. The spots were located by spraying the plates first with sulphuric acid and then with k0% solution of Formaldehyde and heating the plate to 100°C for 3 to 5 minutes. The Rf values were calculated. It is given in Table 7. 

Remove the staples from the dried chromatogram. Mark the spots of the pigments by circling with a pencil. Note the colors of the spots. Measure the distance of the center of each spot from its origin. Calculate the Rf values. 

Record the distance the solvent front advanced on your Report Sheet (4). Record on your Report Sheet (5-9) the distance of each iodine-stained spot from its origin. Calculate the Rf values of your samples (10-14). 

Remove the plates from the oven. Mark the center of the spots and calculate the Rf values of each spot. Record your observations on the Report Sheet. 

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